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  • 1.
    Almqvist, Bjarne
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Björk, Andreas
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences. CSIRO, Mineral Resources, Bradfield Road, West Lindfield, NSW 2070, Australia.
    Mattsson, Hannes B.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Mineralogy Petrology and Tectonics.
    Hedlund, Daniel
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Gunnarsson, Klas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Malehmir, Alireza
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Högdahl, Karin
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Mineralogy Petrology and Tectonics.
    Bäckström, Emma
    Nordic Iron Ore, Ludvika, Sweden.
    Marsden, Paul
    Nordic Iron Ore, Ludvika, Sweden.
    Magnetic characterisation of magnetite and hematite from the Blötberget apatite-iron-oxide deposits (Bergslagen), south-central Sweden2019In: Canadian journal of earth sciences (Print), ISSN 0008-4077, E-ISSN 1480-3313, Vol. 56, no 9, p. 948-957Article in journal (Refereed)
    Abstract [en]

    Rock magnetic measurements were carried out on drill core material and hand specimens from the Blötberget apatite-iron oxide deposit in the Bergslagen ore province, south-central Sweden, to characterise their magnetic properties. Measurements included several kinds of magnetic susceptibility and hysteresis parameters. Petrographic and scanning electron microscopy (SEM) were used to independently identify and quantify the amount and type of magnetite and hematite. Two hematite-rich samples were studied with laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) to quantify the trace element chemistry in hematite and investigate the potential influence of trace elements on magnetic properties. Three aspects of this study are noteworthy. 1) Hematite-rich samples display strong anisotropy of magnetic susceptibility, which is likely to affect the appearance and modelling of magnetic anomalies. 2) The magnitude-drop in susceptibility across Curie and Néel temperature transitions show significant correlation with the respective weight percent (wt%) of magnetite and hematite. Temperature dependent magnetic susceptibility measurements can therefore be used to infer the amounts of both magnetite and hematite. 3) observations of a strongly depressed Morin transition at ca -60 to -70 C (200 to 210 K) are made during low-temperature susceptibility measurements. This anomalous Morin transition is most likely related to trace amounts of V and Ti that substitute for Fe in the hematite. When taken together, these magnetic observations improve the understanding of the magnetic anomaly signature of the Blötberget apatite-iron oxide deposits and may potentially be utilised in a broader context when assessing similar (Paleoproterozoic) apatite-iron oxide systems.

  • 2.
    Breijaert, T. C.
    et al.
    Swedish Univ Agr Sci, Dept Mol Sci Bioctr, Almas 5, SE-756 51 Uppsala, Sweden.
    Daniel, G.
    Swedish Univ Agr Sci, Dept Forest Biomat & Technol Wood Sci, Vallvagen 9C-D, S-756 51 Uppsala, Sweden.
    Hedlund, Daniel
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Solid State Physics.
    Svedlindh, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Solid State Physics.
    Kessler, V. G.
    Swedish Univ Agr Sci, Dept Mol Sci Bioctr, Almas 5, SE-756 51 Uppsala, Sweden.
    Granberg, H.
    Res Inst Sweden RISE, Dept Mat & Surface Design Smart Mat, Drottning Kristinas vag 61, S-114 28 Stockholm, Sweden.
    Hakansson, K.
    Res Inst Sweden RISE, Dept Mat & Surface Design Smart Mat, Drottning Kristinas vag 61, S-114 28 Stockholm, Sweden.
    Seisenbaeva, G. A.
    Swedish Univ Agr Sci, Dept Mol Sci Bioctr, Almas 5, SE-756 51 Uppsala, Sweden.
    Self-assembly of ferria-nanocellulose composite fibres2022In: Carbohydrate Polymers, ISSN 0144-8617, E-ISSN 1879-1344, Vol. 291, article id 119560Article in journal (Refereed)
    Abstract [en]

    An environmentally benign synthesis of a magnetically responsive carboxymethylated cellulose nanofibril-based material is reported. Applied experimental conditions lead to the in-situ formation of magnetite nanoparticles with primary particle sizes of 2.0-4.0 nm or secondary particles of 3.6-16.4 nm depending on whether nucleation occurred between individual carboxymethylated cellulose nanofibrils, or on exposed fibril surfaces. The increase in magnetite particle size on the cellulose fibril surfaces was attributed to Ostwald ripening, while the small particles formed within the carboxymethyl cellulose aggregates were presumably due to steric interactions. The magnetite nanoparticles were capable of coordinating to carboxymethylated cellulose nanofibrils to form large "fibre-like" assemblies. The confinement of small particles within aggregates of reductive cellulose molecules was most likely responsible for excellent conservation of magnetic characteristics on storage of this material. The possibility for using the material in drug delivery applications with release rate controlled by daylight illumination is presented.

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  • 3.
    Cedervall, Johan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
    Nonnet, Elise
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström.
    Hedlund, Daniel
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Häggström, Lennart
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Ericsson, Tore
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Werwinski, Miroslaw
    Institute of Molecular Physics, Polish Academy of Sciences.
    Edström, Alexander
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Department of Materials Theory, ETH Zürich.
    Rusz, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Svedlindh, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Gunnarsson, Klas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Sahlberg, Martin
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
    Influence of cobalt substitution on the magnetic properties of Fe5PB22018In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 57, no 2, p. 777-784Article in journal (Refereed)
    Abstract [en]

    In this study the effects of cobalt substitutions in Fe5PB2 have been studied. An increased cobalt content reduces the magnetic exchange interactions. This has been concluded from a large, linear decrease in both the Curie temperature as well as the saturated magnetic moment. At high cobalt concentrations, cobalt prefers to order at the M(2) position in the crystal structure. A tunable Curie transition like this shows some prerequisites for magnetic cooling applications.

    The substitutional effects of cobalt in (Fe1–xCox)5PB2 have been studied with respect to crystalline structure and chemical order with X-ray diffraction and Mössbauer spectroscopy. The magnetic properties have been determined from magnetic measurements, and density functional theory calculations have been performed for the magnetic properties of both the end compounds, as well as the chemically disordered intermediate compounds. The crystal structure of (Fe1–xCox)5PB2 is tetragonal (space group I4/mcm) with two different metal sites, with a preference for cobalt atoms in the M(2) position (4c) at higher cobalt contents. The substitution also affects the magnetic properties with a decrease of the Curie temperature (TC) with increasing cobalt content, from 622 to 152 K for Fe5PB2 and (Fe0.3Co0.7)5PB2, respectively. Thus, the Curie temperature is dependent on composition, and it is possible to tune TC to a temperature near room temperature, which is one prerequisite for magnetic cooling materials.

  • 4.
    Clulow, Rebecca
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
    Hedlund, Daniel
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Solid State Physics.
    Vishina, Alena
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Svedlindh, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Solid State Physics.
    Sahlberg, Martin
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
    Magnetic and Structural Properties of the Fe5Si1-xGexB2 System2022In: Journal of Solid State Chemistry, ISSN 0022-4596, E-ISSN 1095-726X, Vol. 316, article id 123576Article in journal (Refereed)
    Abstract [en]

    A series of compounds with compositions Fe5Si1-xGexB2 were synthesised and their structural and magnetic properties were investigated. The Mo5SiB2-type structure with tetragonal I4/mcm space group is maintained for all compounds with x < 0.15, which is estimated as the compositional limit of the system. The unit cell pa-rameters expand with Ge content before reaching a plateau of a = 5.5581(1) and c = 10.3545(1) angstrom at x = 0.15. The saturation magnetisation (MS) decreased slightly with increasing Ge content whilst the magnetocrystalline anisotropy energy (MAE) remains almost unaffected. The Curie temperature for all compounds studied is at 790 K whilst the spin-reorientation temperature shows suppression from 172 K to 101 K where x = 0.15. Ab Initio calculations reveal an increase in MAE for compositions up to x = 0.25 and a decreased magnitude of MAE of-0.14 MJ/m3 for the hypothetical compound Fe5GeB2 relative to the parent compound Fe5SiB2.

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  • 5.
    Fang, Hailiang
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
    Cedervall, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
    Hedlund, Daniel
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Shafeie, Samrand
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
    Deledda, Stefano
    Olsson, Fredrik
    von Fieandt, Linus
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
    Bednarcik, Jozef
    Svedlindh, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Gunnarsson, Klas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Sahlberg, Martin
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
    Structural, microstructural and magnetic evolution in cryo milled carbon doped MnAl2018In: Scientific Reports, E-ISSN 2045-2322, Vol. 8, no 1, article id 2525Article in journal (Refereed)
    Abstract [en]

    The low cost, rare earth free τ-phase of MnAl has high potential to partially replace bonded Nd2Fe14B rare earth permanent magnets. However, the τ-phase is metastable and it is experimentally difficult to obtain powders suitable for the permanent magnet alignment process, which requires the fine powders to have an appropriate microstructure and high τ-phase purity. In this work, a new method to make high purity τ-phase fne powders is presented. A high purity τ-phase Mn0.55Al0.45C0.02 alloy was synthesized by the drop synthesis method. The drop synthesized material was subjected to cryo milling and followed by a fash heating process. The crystal structure and microstructure of the drop synthesized, cryo milled and flash heated samples were studied by X-ray in situ powder diffraction, scanning electron microscopy, X-ray energy dispersive spectroscopy and electron backscatter diffraction. Magnetic properties and magnetic structure of the drop synthesized, cryo milled, flash heated samples were characterized by magnetometry and neutron powder diffraction, respectively. The results reveal that the 2 and 4hours cryo milled and flash heated samples both exhibit high τ-phase purity and micron-sized round particle shapes. Moreover, the fash heated samples display high saturation magnetization as well as increased coercivity.

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  • 6.
    Fang, Hailiang
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
    Li, Jiheng
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry. Univ Sci & Technol Beijing, State Key Lab Adv Met & Mat, Beijing, Peoples R China.
    Shafeie, Samrand
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
    Hedlund, Daniel
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Cedervall, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
    Ekström, Fredrik
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Gómez, Cesar Pay
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Bednarcik, Jozef
    Deutsch Elektronen Synchrotron DESY, Notkestr 85, D-22603 Hamburg, Germany.
    Svedlindh, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Gunnarsson, Klas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Sahlberg, Martin
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
    Insights into phase transitions and magnetism of MnBi crystals synthesized from self-flux2019In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 781, p. 308-314Article in journal (Refereed)
    Abstract [en]

    To effectively synthesize high purity ferromagnetic low temperature phase (LTP) MnBi with optimal microstructure is still a challenge that needs to be overcome for the system to reach its full potential. Here, the phase transitions and magnetic properties of MnBi crystals are reported. The phase transition between the low and high temperature structure of MnBi was systematically investigated at different heating/cooling rates using in situ synchrotron radiation X-ray diffraction. The material crystallizes in a layered hexagonal structure giving a platelike microstructure. The magnetic characterization of the crystals reveal that the saturation magnetization varies from 645 kA/m at 50 K to 546 kA/m at 300 K. Magnetization measurements also show that the sample upon heating becomes non-magnetic and transforms to the high temperature phase (HTP) at similar to 640 K, and that it regains ferromagnetic properties and transforms back to the LTP at similar to 610 K upon subsequent cooling.

  • 7.
    Ghorai, Sagar
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Solid State Physics.
    Hedlund, Daniel
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Solid State Physics.
    Kapuscinski, Martin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Solid State Physics.
    Svedlindh, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Solid State Physics.
    A setup for direct measurement of the adiabatic temperature change in magnetocaloric materials2023In: IEEE Transactions on Instrumentation and Measurement, ISSN 0018-9456, E-ISSN 1557-9662, Vol. 72, p. 1-9Article in journal (Refereed)
    Abstract [en]

    In order to find a highly efficient, environmentally-friendly magnetic refrigerant, direct measurements of the adiabatic temperature change ΔTadb are required. Here, in this work, a simple setup for the ΔTadb measurement is presented. Using a permanent magnet Halbach array with a maximum magnetic field of 1.8 T and a rate of magnetic field change of 5 T/s, accurate determination of ΔTadb is possible in this system. The operating temperature range of the system is from 100 to 400 K, designed for the characterization of materials with potential for room temperature magnetic refrigeration applications. Using the setup, ΔTadb of a first-order and two second-order compounds have been studied. Results from the direct measurement for the first-order compound have been compared with ΔTadb calculated from the temperature and magnetic field-dependent specific heat data. By comparing results from direct and indirect measurements, it is concluded that for a reliable characterization of the magnetocaloric effect (MCE), direct measurement of ΔTadb should be adopted.

  • 8.
    Ghorai, Sagar
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Solid State Physics.
    Skini, Ridha
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Solid State Physics.
    Hedlund, Daniel
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Solid State Physics.
    Ström, Petter
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
    Svedlindh, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Solid State Physics.
    Field induced crossover in critical behaviour and direct measurement of the magnetocaloric properties of La0.4Pr0.3Ca0.1Sr0.2MnO32020In: Scientific Reports, E-ISSN 2045-2322, Vol. 10, article id 19485Article in journal (Refereed)
    Abstract [en]

    La0.4Pr0.3Ca0.1Sr0.2MnO3 has been investigated as a potential candidate for room temperature magnetic refrigeration. Results from X-ray powder diffraction reveal an orthorhombic structure with Pnma space group. The electronic and chemical properties have been confirmed by X-ray photoelectron spectroscopy and ion-beam analysis. A second-order paramagnetic to ferromagnetic transition was observed near room temperature (289 K), with a mean-field like critical behaviour at low field and a tricritical mean-field like behaviour at high field. The field induced crossover in critical behaviour is a consequence of the system being close to a first-order magnetic transition in combination with a magnetic field induced suppression of local lattice distortions. The lattice distortions consist of interconnected and weakly distorted pairs of Mn-ions, where each pair shares an electron and a hole, dispersed by large Jahn–Teller distortions at Mn3+ lattice sites. A comparatively high value of the isothermal entropy-change (3.08 J/kg-K at 2 T) is observed and the direct measurements of the adiabatic temperature change reveal a temperature change of 1.5 K for a magnetic field change of 1.9 T.

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  • 9.
    Hedlund, Daniel
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Solid State Physics. Uppsala university.
    New and old materials for permanent magnets based on earth-abundant elements2022Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Electrical motors, which find use in e.g. electrical vehicles, require per-manent magnets to function. Comparing ferrite magnets and Nd-based magnets reveals a large difference in their price and performance. During the last decade, gap-magnets, with performance in between ferrites and Nd-based magnets have attracted considerable research interest world-wide due to the “rare-earth crisis”. During this crisis, the price of certain rare-earth elements experienced volatile changes. This thesis deals with materials that could be relevant as gap-magnets. The thesis starts with introducing key properties and constraints relevant for gap-magnets. In the thesis, four different systems were investigated. The four systems show that permanent magnets need to be understood and optimized on three distinct levels, the crystal level, the structural level, and the micro-structural level. They show how old and new materials can potentially be utilized as permanent magnets. Lastly, the thesis ends with an outlook that presents new ideas for finding new permanent magnets. The ideas presented in the outlook are ideas that were not treated in this thesis, and thus may represent new ways for further work in developing materials for gap-magnets. 

    List of papers
    1. Magnetic properties of the Fe5SiB2−Fe5PB2 system
    Open this publication in new window or tab >>Magnetic properties of the Fe5SiB2−Fe5PB2 system
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    2017 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, no 9, article id 094433Article in journal (Refereed) Published
    Abstract [en]

    The magnetic properties of the compound Fe5Si1−xPxB2 have been studied, with a focus on the Curie temperature TC, saturation magnetization MS, and magnetocrystalline anisotropy. Field and temperature dependent magnetization measurements were used to determine TC(x) and MS(x). The saturation magnetization at 10 K (300 K) is found to monotonically decrease from 1.11MA/m (1.03MA/m) to 0.97MA/m (0.87MA/m), as x increases from 0 to 1. The Curie temperature is determined to be 810 and 615 K in Fe5SiB2 and Fe5PB2, respectively. The highest TC is observed for x=0.1, while it decreases monotonically for larger x. The Curie temperatures have also been theoretically determined to be 700 and 660 K for Fe5SiB2 and Fe5PB2, respectively, using a combination of density functional theory and Monte Carlo simulations. The magnitude of the effective magnetocrystalline anisotropy was extracted using the law of approach to saturation, revealing an increase with increasing phosphorus concentration. Low-field magnetization vs temperature results for x=0,0.1,0.2 indicate that there is a transition from easy-axis to easy-plane anisotropy with decreasing temperature.

    Place, publisher, year, edition, pages
    American Physical Society, 2017
    Keywords
    Magnetism, Ferromagnetism, First-principle calculations, Magnetic interactions, Magnetic order parameter, Magnetic phase transition
    National Category
    Condensed Matter Physics Engineering and Technology
    Research subject
    Physics
    Identifiers
    urn:nbn:se:uu:diva-330463 (URN)10.1103/PhysRevB.96.094433 (DOI)000411975700001 ()
    Funder
    Swedish Research CouncilGöran Gustafsson Foundation for Research in Natural Sciences and MedicineKnut and Alice Wallenberg Foundation, 2013.0020, 2012.0031EU, Horizon 2020
    Available from: 2017-09-29 Created: 2017-09-29 Last updated: 2022-05-24Bibliographically approved
    2. Magnetocrystalline anisotropy of Fe5PB2 and its alloys with Co and 5d elements: A combined first-principles and experimental study
    Open this publication in new window or tab >>Magnetocrystalline anisotropy of Fe5PB2 and its alloys with Co and 5d elements: A combined first-principles and experimental study
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    2018 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 98, no 21, article id 214431Article in journal (Refereed) Published
    Abstract [en]

    The Fe5PB2 compound offers tunable magnetic properties via the possibility of various combinations of substitutions on the Fe and P sites. Here, we present a combined computational and experimental study of the magnetic properties of (Fe1-xCox)(5)PB2. Computationally, we are able to explore the full concentration range, while the real samples were only obtained for 0 <= x <= 0.7. The calculated magnetic moments, Curie temperatures, and magnetocrystalline anisotropy energies (MAEs) are found to decrease with increasing Co concentration. Co substitution allows for tuning the Curie temperature in a wide range of values, from about six hundred to zero kelvins. As the MAE depends on the electronic structure in the vicinity of the Fermi energy, the geometry of the Fermi surface of Fe5PB2 and the k-resolved contributions to the MAE are discussed. Low-temperature measurements of an effective anisotropy constant for a series of (Fe1-xCox)(5)PB2 samples determined the highest value of 0.94 MJ m(-3) for the terminal Fe5PB2 composition, which then decreases with increasing Co concentration, thus confirming the computational result that Co alloying of Fe5PB2 is not a good strategy to increase the MAE of the system. However, the relativistic version of the fixed spin moment method reveals that a reduction in the magnetic moment of Fe5PB2, by about 25%, produces a fourfold increase of the MAE. Furthermore, calculations for (Fe0.95X0.05)(5)PB2 (X = 5d element) indicate that 5% doping of Fe5PB2 with W or Re should double the MAE. These are results of high interest for, e.g., permanent magnet applications, where a large MAE is crucial.

    National Category
    Condensed Matter Physics
    Identifiers
    urn:nbn:se:uu:diva-373233 (URN)10.1103/PhysRevB.98.214431 (DOI)000454163400003 ()
    Funder
    Swedish Research CouncilSwedish Foundation for Strategic Research
    Available from: 2019-01-14 Created: 2019-01-14 Last updated: 2022-04-26Bibliographically approved
    3. Influence of cobalt substitution on the magnetic properties of Fe5PB2
    Open this publication in new window or tab >>Influence of cobalt substitution on the magnetic properties of Fe5PB2
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    2018 (English)In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 57, no 2, p. 777-784Article in journal (Refereed) Published
    Abstract [en]

    In this study the effects of cobalt substitutions in Fe5PB2 have been studied. An increased cobalt content reduces the magnetic exchange interactions. This has been concluded from a large, linear decrease in both the Curie temperature as well as the saturated magnetic moment. At high cobalt concentrations, cobalt prefers to order at the M(2) position in the crystal structure. A tunable Curie transition like this shows some prerequisites for magnetic cooling applications.

    The substitutional effects of cobalt in (Fe1–xCox)5PB2 have been studied with respect to crystalline structure and chemical order with X-ray diffraction and Mössbauer spectroscopy. The magnetic properties have been determined from magnetic measurements, and density functional theory calculations have been performed for the magnetic properties of both the end compounds, as well as the chemically disordered intermediate compounds. The crystal structure of (Fe1–xCox)5PB2 is tetragonal (space group I4/mcm) with two different metal sites, with a preference for cobalt atoms in the M(2) position (4c) at higher cobalt contents. The substitution also affects the magnetic properties with a decrease of the Curie temperature (TC) with increasing cobalt content, from 622 to 152 K for Fe5PB2 and (Fe0.3Co0.7)5PB2, respectively. Thus, the Curie temperature is dependent on composition, and it is possible to tune TC to a temperature near room temperature, which is one prerequisite for magnetic cooling materials.

    National Category
    Inorganic Chemistry Condensed Matter Physics Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-331758 (URN)10.1021/acs.inorgchem.7b02663 (DOI)000422810900030 ()29298054 (PubMedID)
    Funder
    Swedish Research CouncilSwedish Energy AgencyEuropean Regional Development Fund (ERDF)
    Available from: 2017-10-19 Created: 2017-10-19 Last updated: 2023-10-31Bibliographically approved
    4. Magnetic and Structural Properties of the Fe5Si1-xGexB2 System
    Open this publication in new window or tab >>Magnetic and Structural Properties of the Fe5Si1-xGexB2 System
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    2022 (English)In: Journal of Solid State Chemistry, ISSN 0022-4596, E-ISSN 1095-726X, Vol. 316, article id 123576Article in journal (Refereed) Published
    Abstract [en]

    A series of compounds with compositions Fe5Si1-xGexB2 were synthesised and their structural and magnetic properties were investigated. The Mo5SiB2-type structure with tetragonal I4/mcm space group is maintained for all compounds with x < 0.15, which is estimated as the compositional limit of the system. The unit cell pa-rameters expand with Ge content before reaching a plateau of a = 5.5581(1) and c = 10.3545(1) angstrom at x = 0.15. The saturation magnetisation (MS) decreased slightly with increasing Ge content whilst the magnetocrystalline anisotropy energy (MAE) remains almost unaffected. The Curie temperature for all compounds studied is at 790 K whilst the spin-reorientation temperature shows suppression from 172 K to 101 K where x = 0.15. Ab Initio calculations reveal an increase in MAE for compositions up to x = 0.25 and a decreased magnitude of MAE of-0.14 MJ/m3 for the hypothetical compound Fe5GeB2 relative to the parent compound Fe5SiB2.

    National Category
    Condensed Matter Physics
    Research subject
    Engineering Science with specialization in Solid State Physics
    Identifiers
    urn:nbn:se:uu:diva-473290 (URN)10.1016/j.jssc.2022.123576 (DOI)000863761000008 ()
    Funder
    Swedish Foundation for Strategic Research, EM-16-0039Swedish Research Council, 2019-00207
    Available from: 2022-04-25 Created: 2022-04-25 Last updated: 2022-10-28Bibliographically approved
    5. Structural, microstructural and magnetic evolution in cryo milled carbon doped MnAl
    Open this publication in new window or tab >>Structural, microstructural and magnetic evolution in cryo milled carbon doped MnAl
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    2018 (English)In: Scientific Reports, E-ISSN 2045-2322, Vol. 8, no 1, article id 2525Article in journal (Refereed) Published
    Abstract [en]

    The low cost, rare earth free τ-phase of MnAl has high potential to partially replace bonded Nd2Fe14B rare earth permanent magnets. However, the τ-phase is metastable and it is experimentally difficult to obtain powders suitable for the permanent magnet alignment process, which requires the fine powders to have an appropriate microstructure and high τ-phase purity. In this work, a new method to make high purity τ-phase fne powders is presented. A high purity τ-phase Mn0.55Al0.45C0.02 alloy was synthesized by the drop synthesis method. The drop synthesized material was subjected to cryo milling and followed by a fash heating process. The crystal structure and microstructure of the drop synthesized, cryo milled and flash heated samples were studied by X-ray in situ powder diffraction, scanning electron microscopy, X-ray energy dispersive spectroscopy and electron backscatter diffraction. Magnetic properties and magnetic structure of the drop synthesized, cryo milled, flash heated samples were characterized by magnetometry and neutron powder diffraction, respectively. The results reveal that the 2 and 4hours cryo milled and flash heated samples both exhibit high τ-phase purity and micron-sized round particle shapes. Moreover, the fash heated samples display high saturation magnetization as well as increased coercivity.

    National Category
    Materials Chemistry Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-341024 (URN)10.1038/s41598-018-20606-8 (DOI)000424189500012 ()29410462 (PubMedID)
    Funder
    Swedish Energy AgencySweGRIDS - Swedish Centre for Smart Grids and Energy StorageSwedish Research Council
    Available from: 2018-02-06 Created: 2018-02-06 Last updated: 2022-09-15Bibliographically approved
    6. One step towards MnAl-based permanent magnets: Differences in magnetic, and microstructural properties from an intermediate annealing step during synthesis
    Open this publication in new window or tab >>One step towards MnAl-based permanent magnets: Differences in magnetic, and microstructural properties from an intermediate annealing step during synthesis
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    2019 (English)In: Journal of Solid State Chemistry, ISSN 0022-4596, E-ISSN 1095-726X, Vol. 274, p. 229-236Article in journal (Refereed) Published
    Abstract [en]

    The influence of an additional annealing step during synthesis on the preparation of MnAl based permanent magnet alloys has been investigated. Bulk samples of Mn55Al45C2 alloys were synthesized using induction heating through drop synthesis from 1400 °C. Samples produced using cooling directly from 1400 °C (from the melt), and from 1400 °C to an intermediate annealing step at 1200 °C for ~ 30 min before cooling were compared with respect to differences in phase purity, microstructure and magnetic properties. We found that the phase purity was significantly enhanced using the route with an intermediate annealing step at 1200 °C. From XRD the phase purity of the tau-phase was improved from ~ 91 wt% for the sample cooled directly from 1400 °C to ~ 95.1 - 99.5 wt% for the sample exposed to an intermediate annealing step before cooling. Additionally, EBSD, and SEM with EDS indicates a clear difference in the phase composition and differences in the distribution of the magnetic tau phase and the non-magnetic epsilon-, beta-, and gamma-phases. Magnetic properties also indicate, an improvement in saturation magnetization for the sample exposed to the extra annealing step during synthesis. Our results suggest that an intermediate annealing step in the production of MnAl based alloys will provide a simple way of achieving better phase purity and magnetic properties in the bulk alloy.

    Keywords
    permanent magnet, rare earth free, microstructure
    National Category
    Materials Chemistry
    Identifiers
    urn:nbn:se:uu:diva-368283 (URN)10.1016/j.jssc.2019.03.035 (DOI)000467663700032 ()
    Funder
    SweGRIDS - Swedish Centre for Smart Grids and Energy StorageSwedish Foundation for Strategic Research
    Available from: 2018-12-03 Created: 2018-12-03 Last updated: 2023-10-31Bibliographically approved
    7. Influence of nano-VC on the structural and magnetic properties of MnAlC-alloy
    Open this publication in new window or tab >>Influence of nano-VC on the structural and magnetic properties of MnAlC-alloy
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    2021 (English)In: Scientific Reports, E-ISSN 2045-2322, Vol. 11, article id 14453Article in journal (Refereed) Published
    Abstract [en]

    Alloys of Mn55Al45C2 with additions of VC nano-particles have been synthesized and their properties evaluated. The Mn55Al45C2(VC)(x) (x=0.25, 0.5 and 1) alloys have been prepared by induction melting resulting in a high content of the ferromagnetic tau -phase (>94 wt.%). Powder X-ray diffraction indicates that nano-VC can be dissolved in the alloy matrix up to 1 at.%. On the other side, metallography investigations by scanning electron microscopy and scanning transmission electron microscope show inclusions of the nanosized additives in the microstructure. The effect of nano-VC on the grain and twin boundaries has been studied by electron backscattering diffraction. The magnetization has been measured by magnetometry up to 9 T while the domain structure has been studied using both magnetic force microscopy as well as Kerr-microscopy. For nano-VC contents above 0.25 at.%, a clear increase of the coercive force is observed, from 57 to 71 kA/m. The optimum appears to be for 0.5 at.% nano-VC which shows a 25% increase in coercive force without losing any saturation magnetization. This independent increase in coercivity is believed to originate from the nano-VC reducing the overall magnetic domain size. Overall, we observe that addition of nano-VC could be an interesting route to increase the coercive force of MnAl, without sacrificing saturation magnetization.

    Place, publisher, year, edition, pages
    Springer NatureNATURE RESEARCH, 2021
    National Category
    Condensed Matter Physics Metallurgy and Metallic Materials
    Identifiers
    urn:nbn:se:uu:diva-452947 (URN)10.1038/s41598-021-93395-2 (DOI)000675633500020 ()34262064 (PubMedID)
    Available from: 2021-09-13 Created: 2021-09-13 Last updated: 2024-01-15Bibliographically approved
    8. Structural and magnetic properties of new members of the 3:29 phase from the Ce-Fe-Mn system and 1:11 from the Ce-Co-Mn
    Open this publication in new window or tab >>Structural and magnetic properties of new members of the 3:29 phase from the Ce-Fe-Mn system and 1:11 from the Ce-Co-Mn
    Show others...
    2021 (English)In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 855, article id 157435Article in journal (Refereed) Published
    Abstract [en]

    The Ce–Fe–Mn and Ce–Co–Mn systems have been re-visited with the intent of finding new potential phases for application as permanent magnets. Two new ternary compounds, Ce3(Fe0.638Mn0.362)29 (Nd3(Fe,Ti)29-type, space group P21/c, No. 14, Pearson Symbol mP128) and CeCo8Mn3 (Ce(Ni,Mn)11-type, space group P4/mbm, No. 127, Pearson Symbol tP24) have been discovered in the compositional range where the Ce2(T,Mn)17 (T = Fe, Co) phases are expected to exist with a (H)–Th2Ni17-type structure (space group P63/mmc, No. 194, Pearson Symbol hP38). Detailed investigations of the crystal structures have been performed using X-ray powder diffraction (XRPD) with supporting energy-dispersive X-ray (EDS) analysis. Compositions of the new compounds have been defined based on the EDS analysis as follows: Ce9.7Fe57.5Mn32.8 and Ce9.2Co65.2Mn25.6. A short discussion on the crystal structure peculiarities of the 1:5, 1:11, 1:12, 2:17 and 3:29 compounds in the Ce–T–Mn (T = Fe, Co, Ni, Cu) systems has been made. We present magnetic measurements on selected representatives of the studied phases. The most interesting being the Ce3(Fe0.638Mn0.362)29 phase which has a transition temperature well above room temperature. CeNi4.95Mn6.05 and CeCo8Mn3 exhibits properties characteristic of a canted antiferromagnetic state.

    Place, publisher, year, edition, pages
    Elsevier, 2021
    Keywords
    Intermetallic compounds, Crystal structure, Magnetic properties
    National Category
    Materials Chemistry Metallurgy and Metallic Materials
    Identifiers
    urn:nbn:se:uu:diva-432623 (URN)10.1016/j.jallcom.2020.157435 (DOI)000601001500058 ()
    Funder
    Swedish Foundation for Strategic Research , EM16-0039Swedish Energy AgencySweGRIDS - Swedish Centre for Smart Grids and Energy Storage
    Available from: 2021-01-25 Created: 2021-01-25 Last updated: 2024-01-15Bibliographically approved
    9. Hard magnetic phases of CeFe11W1-xTix
    Open this publication in new window or tab >>Hard magnetic phases of CeFe11W1-xTix
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    (English)Manuscript (preprint) (Other academic)
    National Category
    Condensed Matter Physics
    Research subject
    Engineering Science with specialization in Solid State Physics
    Identifiers
    urn:nbn:se:uu:diva-473289 (URN)
    Available from: 2022-04-25 Created: 2022-04-25 Last updated: 2022-04-26
    10. Magnetic Structure and Properties of CeFe12-xMnx
    Open this publication in new window or tab >>Magnetic Structure and Properties of CeFe12-xMnx
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    (English)Manuscript (preprint) (Other academic)
    National Category
    Condensed Matter Physics
    Identifiers
    urn:nbn:se:uu:diva-473375 (URN)
    Available from: 2022-04-26 Created: 2022-04-26 Last updated: 2022-04-26
    11. Data-driven design of a new class of rare-earth free permanent magnets
    Open this publication in new window or tab >>Data-driven design of a new class of rare-earth free permanent magnets
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    2021 (English)In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 212, article id 116913Article in journal (Refereed) Published
    Abstract [en]

    A new class of rare-earth-free permanent magnets is proposed. The parent compound of this class is Co3Mn2Ge, and its discovery is the result of first principles theory combined with experimental synthesis and characterisation. The theory is based on a high-throughput/data-mining search among materials listed in the ICSD database. From ab-initio theory of the defect free material it is predicted that the saturation magnetization is 1.71 T, the uniaxial magnetocrystalline anisotropy is 1.44 MJ/m3, and the Curie temperature is 700 K. Co3Mn2Ge samples were then synthesized and characterised with respect to structure and magnetism. The crystal structure was found to be the MgZn2-type, with partial disorder of Co and Ge on the crystallographic lattice sites. From magnetization measurements a saturation polarization of 0.86 T at 10 K was detected, together with a uniaxial magnetocrystalline anisotropy constant of 1.18 MJ/m3, and the Curie temperature of TC = 359 K. These magnetic properties make Co3Mn2Ge a very promising material as a rare-earth free permanent magnet, and since we can demonstrate that magnetism depends critically on the amount of disorder of the Co and Ge atoms, a further improvement of the magnetism is possible. We demonstrate here that the class of compounds based on T3Mn2X (T = Co or alloys between Fe and Ni; X = Ge, Al or Ga) in the MgZn2 structure type, form a new class of rare-earth free permanent magnets with very promising performance.

    Place, publisher, year, edition, pages
    Elsevier, 2021
    Keywords
    Permanent magnets, Rare-earth, Synthesis, DFT, Magnetism
    National Category
    Condensed Matter Physics Materials Chemistry
    Identifiers
    urn:nbn:se:uu:diva-448912 (URN)10.1016/j.actamat.2021.116913 (DOI)000663657100005 ()
    Funder
    VinnovaSwedish Foundation for Strategic Research SweGRIDS - Swedish Centre for Smart Grids and Energy StorageSwedish Energy AgencySwedish Research CouncilKnut and Alice Wallenberg FoundationStandUpSwedish National Infrastructure for Computing (SNIC)
    Available from: 2021-07-12 Created: 2021-07-12 Last updated: 2024-01-15Bibliographically approved
    12. Influence of Mn/Co ratio on the magnetic properties of the hexagonal Mn(Co,Ge)2 phase
    Open this publication in new window or tab >>Influence of Mn/Co ratio on the magnetic properties of the hexagonal Mn(Co,Ge)2 phase
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    (English)Manuscript (preprint) (Other academic)
    National Category
    Condensed Matter Physics
    Research subject
    Engineering Science with specialization in Solid State Physics
    Identifiers
    urn:nbn:se:uu:diva-473291 (URN)
    Available from: 2022-04-25 Created: 2022-04-25 Last updated: 2022-10-06
    13. Revealing the Magnetic Structure and Properties of Mn(Co,Ge)2
    Open this publication in new window or tab >>Revealing the Magnetic Structure and Properties of Mn(Co,Ge)2
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    2022 (English)In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 61, no 44, p. 17673-17681Article in journal (Refereed) Published
    Abstract [en]

    The atomic and magnetic structures of Mn(Co,Ge)2 are reported herein. The system crystallizes in the space group P63/mmc as a superstructure of the MgZn2-type structure. The system exhibits two magnetic transitions with associated magnetic structures, a ferromagnetic (FM) structure around room temperature, and an incommensurate structure at lower temperatures. The FM structure, occurring between 193 and 329 K, is found to be a member of the magnetic space group P63/mmc′. The incommensurate structure found below 193 K is helical with propagation vector k = (0 0 0.0483). Crystallographic results are corroborated by magnetic measurements and ab initio calculations.

    Place, publisher, year, edition, pages
    American Chemical Society (ACS), 2022
    National Category
    Condensed Matter Physics
    Identifiers
    urn:nbn:se:uu:diva-473292 (URN)10.1021/acs.inorgchem.2c02758 (DOI)000877353500001 ()36270053 (PubMedID)
    Funder
    Swedish Foundation for Strategic Research, EM-16-0039eSSENCE - An eScience CollaborationSwedish National Infrastructure for Computing (SNIC), snic2021-1-36Swedish National Infrastructure for Computing (SNIC), snic2021-5-340Swedish Research Council, 2019-00645Knut and Alice Wallenberg Foundation
    Available from: 2022-04-25 Created: 2022-04-25 Last updated: 2023-02-22Bibliographically approved
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    Errata
  • 10.
    Hedlund, Daniel
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Cedervall, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
    Edström, Alexander
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Materials Theory, ETH Zürich.
    Werwinski, Miroslaw
    Polish Academy of Sciences.
    Kontos, Sofia
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Örebro University.
    Rusz, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Svedlindh, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Sahlberg, Martin
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
    Gunnarsson, Klas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Magnetic properties of the Fe5SiB2−Fe5PB2 system2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, no 9, article id 094433Article in journal (Refereed)
    Abstract [en]

    The magnetic properties of the compound Fe5Si1−xPxB2 have been studied, with a focus on the Curie temperature TC, saturation magnetization MS, and magnetocrystalline anisotropy. Field and temperature dependent magnetization measurements were used to determine TC(x) and MS(x). The saturation magnetization at 10 K (300 K) is found to monotonically decrease from 1.11MA/m (1.03MA/m) to 0.97MA/m (0.87MA/m), as x increases from 0 to 1. The Curie temperature is determined to be 810 and 615 K in Fe5SiB2 and Fe5PB2, respectively. The highest TC is observed for x=0.1, while it decreases monotonically for larger x. The Curie temperatures have also been theoretically determined to be 700 and 660 K for Fe5SiB2 and Fe5PB2, respectively, using a combination of density functional theory and Monte Carlo simulations. The magnitude of the effective magnetocrystalline anisotropy was extracted using the law of approach to saturation, revealing an increase with increasing phosphorus concentration. Low-field magnetization vs temperature results for x=0,0.1,0.2 indicate that there is a transition from easy-axis to easy-plane anisotropy with decreasing temperature.

  • 11.
    Hedlund, Daniel
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Solid State Physics.
    Rosenqvist Larsen, Simon
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
    Sahlberg, Martin
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
    Svedlindh, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Solid State Physics.
    Shtender, Vitalii
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Applied Material Science.
    Influence of Mn content on the magnetic properties of the hexagonal Mn (Co,Ge)2 phase2023In: Scripta Materialia, ISSN 1359-6462, E-ISSN 1872-8456, Vol. 233, article id 115534Article in journal (Refereed)
    Abstract [en]

    Herein, we report on the effect of Mn content on the magnetic properties of the hexagonal Mn(Co,Ge)2 with composition Mn36+xCo49-xGe15.This compound was previously described as Mn2Co3Ge (MgZn2-type structure), but later as Mn(Co,Ge)2 with its own structure type, all samples in this work follow the same superstructure model. Samples were synthesized by induction melting, the crystal structures were evaluated using a combination of X-ray diffraction together with scanning electron microscopy equipped and an energy dispersive X-ray spectroscopy detector. The Curie temperature (TC) is shifted towards lower temperature as the Mn content is increased. On the other hand, the spin reorientation temperature (TSRT) increases and the magnetic moment decreases as the Mn content is increased. The magnetocaloric properties were investigated for the x = 1 alloy, Mn37Co48Ge15. It was found that the isothermal entropy change is 2 J kg−1 K−1 at room temperature for an applied field of 5 T.

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    fulltext
  • 12.
    Jana, Somnath
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics. Indian Inst Sci, Solid State & Struct Chem Unit, Bengaluru 560012, India;Helmholtz Zentrum Berlin FG ISRR, Albert Einstein Str 15, D-12489 Berlin, Germany.
    Panda, S. K.
    Univ Paris Saclay, Ctr Phys Theor, Ecole Polytech, CNRS UMR 7644, F-91128 Palaiseau, France;Bennett Univ, Dept Phys, Greater Noida 201310, Uttar Pradesh, India.
    Phuyal, Dibya
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Pal, B.
    Indian Inst Sci, Solid State & Struct Chem Unit, Bengaluru 560012, India.
    Mukherjee, Soham
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics. Indian Inst Sci, Solid State & Struct Chem Unit, Bengaluru 560012, India.
    Dutta, A.
    Indian Inst Sci, Solid State & Struct Chem Unit, Bengaluru 560012, India.
    Anil Kumar, Puri
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics. Seagate Technol, 1 Disc Dr, Springtown BT48 0BF, North Ireland.
    Hedlund, Daniel
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Schött, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Thunström, Patrik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Kvashnin, Yaroslav
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Rensmo, Håkan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Kamalakar, M. Venkata
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Segre, Carlo U.
    IIT, CSRRI, Chicago, IL 60616 USA;IIT, Dept Phys, Chicago, IL 60616 USA.
    Svedlindh, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Gunnarsson, Klas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Biermann, S.
    Univ Paris Saclay, Ctr Phys Theor, Ecole Polytech, CNRS UMR 7644, F-91128 Palaiseau, France;Coll France, 11 Pl Marcelin Berthelot, F-75005 Paris, France.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Orebro Univ, Sch Sci & Technol, SE-70182 Orebro, Sweden.
    Karis, Olof
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Sarma, D. D.
    Indian Inst Sci, Solid State & Struct Chem Unit, Bengaluru 560012, India.
    Charge disproportionate antiferromagnetism at the verge of the insulator-metal transition in doped LaFeO32019In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 99, no 7, article id 075106Article in journal (Refereed)
    Abstract [en]

    We explore the effects of electron doping in lanthanum ferrite, LaFeO3 by doping Mo at the Fe sites. Based on magnetic, transport, scanning tunneling spectroscopy, and x-ray photoelectron spectroscopy measurements, we find that the large gap, charge-transfer, antiferromagnetic (AFM) insulator LaFeO3 becomes a small gap AFM band insulator at low Mo doping. With increasing doping concentration, Mo states, which appear around the Fermi level, is broadened and become gapless at a critical doping of 20%. Using a combination of calculations based on density functional theory plus Hubbard U (DFT+U) and x-ray absorption spectroscopy measurements, we find that the system shows charge disproportionation (CD) in Fe ions at 25% Mo doping, where two distinct Fe sites, having Fe2+ and Fe3+ nominal charge states appear. A local breathing-type lattice distortion induces the charge disproportionation at the Fe site without destroying the antiferromagnetic order. Our combined experimental and theoretical investigations establish that the Fe states form a CD antiferromagnet at 25% Mo doping, which remains insulating, while the appearance of Mo states around the Fermi level is showing an indication towards the insulator-metal transition.

  • 13.
    Jana, Somnath
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Panda, Swarup
    Phuyal, Dibya
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Pal, Banabir
    Mukherjee, Soham
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Dutta, Anirban
    Kumar, Ankit
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Hedlund, Daniel
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Schött, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Thunström, Patrik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Kvashnin, Yaroslav
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Rensmo, Håkan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Kamalakar, M. Venkata
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Segre, Carlo U.
    Svedlindh, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Gunnarsson, Klas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Biermann, Silke
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Karis, Olof
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Sarma, D.D.
    Doping induced site-selective Mott insulating phase in LaFeO3Manuscript (preprint) (Other academic)
    Abstract [en]

    Tailoring transport properties of strongly correlated electron systems in a controlled fashion counts among the dreams of materials scientists. In copper oxides, vary- ing the carrier concentration is a tool to obtain high- temperature superconducting phases. In manganites, dop- ing results in exotic physics such as insulator-metal tran- sitions (IMT), colossal magnetoresistance (CMR), orbital- or charge-ordered (CO) or charge-disproportionate (CD) states. In most oxides, antiferromagnetic order and CD phase is asssociated with insulating behavior. Here we re- port the realization of a unique physical state that can be induced by Mo doping in LaFeO3: the resulting metallic state is a site-selective Mott insulator where itinerant elec- trons evolving on low-energy Mo states coexist with local- ized carriers on the Fe sites. In addition, a local breathing- type lattice distortion induces charge disproportionation on the latter, without destroying the antiferromagnetic order. A state, combining antiferromangetism, metallic- ity and CD phenomena is rather rare in oxides and have utmost significance for future antiferromagnetic memory devices.

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    fulltext
  • 14.
    Larsen, Simon R.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
    Hedlund, Daniel
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Solid State Physics.
    Stopfel, Henry
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Solid State Physics.
    Karlsson, Dennis
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
    Christensen, Christian K.
    DESY, Photon Sci Div, Notkestr 85, D-22607 Hamburg, Germany.
    Svedlindh, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Solid State Physics.
    Cedervall, Johan
    Stockholm Univ, Dept Mat & Environm Chem, S-10691 Stockholm, Sweden.
    Magnetic properties and thermal stability of B2 and bcc phases in AlCoCrFeMnxNi2021In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 861, article id 158450Article in journal (Refereed)
    Abstract [en]

    Alloys of AlCoCrFeMnxNi (x = 0.0, 0.04, 0.08, 0.12 and 0.16) have been synthesized through arc–melting and gas atomisation (x = 0.0 and 0.16) to investigate the effect of Mn additions to AlCoCrFeNi. Here, the structure, magnetic properties and the thermal stability of the alloys is presented. Electron microscopy confirmed the elemental composition and revealed the microstructure to consist of two spinodally decomposed phases. Rietveld analysis of standard powder X-ray diffraction showed the arc-melted samples consisted of two phases, a B2 phase and a bcc phase while the gas atomised powders consisted of a single-phased B2 structure. Magnetic measurements revealed an increase in the saturation magnetisation at room temperature by 68% for AlCoCrFeMnNi compared to AlCoCrFeNi. The thermal stability of the alloys was investigated using magnetometry, differential scanning calorimetry and in–situ X-ray diffraction, which showed that an increase in Mn content adversely effected the thermal stability of the alloy.

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  • 15.
    Larsen, Simon R.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
    Shtender, Vitalii
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
    Hedlund, Daniel
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Solid State Physics.
    Delczeg-Czirjak, Erna K.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Beran, Premysl
    Nuclear Physics Institute, ASCR, Hlavni 130, 25068 Rez, Czech Republic; European Spallation Source ESS ERIC, Box 176, 221 00, Lund, Sweden.
    Cedervall, Johan
    Department of Materials and Environmental Chemistry, Stockholm University, 10691 Stockholm, Sweden.
    Vishina, Alena
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Hansen, Thomas C.
    Institut Laue-Langevin, 71 avenue des Martyrs, 38000 Grenoble, France.
    Herper, Heike C.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Svedlindh, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Solid State Physics.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. School of Science and Technology, Örebro University, SE-701 82 Örebro, Sweden.
    Sahlberg, Martin
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
    Revealing the Magnetic Structure and Properties of Mn(Co,Ge)22022In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 61, no 44, p. 17673-17681Article in journal (Refereed)
    Abstract [en]

    The atomic and magnetic structures of Mn(Co,Ge)2 are reported herein. The system crystallizes in the space group P63/mmc as a superstructure of the MgZn2-type structure. The system exhibits two magnetic transitions with associated magnetic structures, a ferromagnetic (FM) structure around room temperature, and an incommensurate structure at lower temperatures. The FM structure, occurring between 193 and 329 K, is found to be a member of the magnetic space group P63/mmc′. The incommensurate structure found below 193 K is helical with propagation vector k = (0 0 0.0483). Crystallographic results are corroborated by magnetic measurements and ab initio calculations.

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  • 16.
    Rosenqvist Larsen, Simon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
    Hedlund, Daniel
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Solid State Physics.
    Clulow, Rebecca
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
    Sahlberg, Martin
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
    Svedlindh, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Solid State Physics.
    Delczeg-Czirjak, Erna Krisztina
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Cedervall, Johan
    Stockholm Univ, Dept Mat & Environm Chem, S-10691 Stockholm, Sweden.;Rutherford Appleton Lab, ISIS Pulsed Neutron & Muon Facil, Harwell Campus, Didcot OX11 0QX, England..
    Magnetism and magnetic structure determination of a selected (Mn,Co)(23)B-6-compound2022In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 905, article id 164225Article in journal (Refereed)
    Abstract [en]

    The vast compositional space in cubic Cr23C6-type compounds (space group Fm3 over line m) opens up possibilities to tune properties by performing substitutions. In this study, the magnetic properties have been explored in a selected (Mn,Co)(23)B-6-compound by the means of synchrotron X-ray diffraction, neutron powder diffraction, magnetometry and electronic structure calculations. Refinements of a structural model based on combined X-ray and neutron diffraction data revealed mixed metal occupancies at all metal positions. However, two sites were richer in Co and the other two showed an abundance of Mn. The magnetic characteristics showed a ferrimagnetic structure below 550 K, with the magnetic moments aligned along the crystallographic c-direction and the magnetic moments on corner atoms having an opposite direction compared to the rest, within the magnetic space group I 4 mm m. The total magnetic moments extracted from magnetometry and neutron diffraction data gave similar values at 6 K, 20.1 and 18.2 mu(B)/f.u., respectively. Results from electronic structure calculations are in reasonable agreement with the experimental findings.& nbsp;(C) 2022 The Author(s). Published by Elsevier B.V. CC_BY_4.0

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  • 17.
    Shafeie, Samrand
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
    Fang, Hailiang
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
    Hedlund, Daniel
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Nyberg, Axel
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Svedlindh, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Gunnarsson, Klas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Sahlberg, Martin
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
    One step towards MnAl-based permanent magnets: Differences in magnetic, and microstructural properties from an intermediate annealing step during synthesis2019In: Journal of Solid State Chemistry, ISSN 0022-4596, E-ISSN 1095-726X, Vol. 274, p. 229-236Article in journal (Refereed)
    Abstract [en]

    The influence of an additional annealing step during synthesis on the preparation of MnAl based permanent magnet alloys has been investigated. Bulk samples of Mn55Al45C2 alloys were synthesized using induction heating through drop synthesis from 1400 °C. Samples produced using cooling directly from 1400 °C (from the melt), and from 1400 °C to an intermediate annealing step at 1200 °C for ~ 30 min before cooling were compared with respect to differences in phase purity, microstructure and magnetic properties. We found that the phase purity was significantly enhanced using the route with an intermediate annealing step at 1200 °C. From XRD the phase purity of the tau-phase was improved from ~ 91 wt% for the sample cooled directly from 1400 °C to ~ 95.1 - 99.5 wt% for the sample exposed to an intermediate annealing step before cooling. Additionally, EBSD, and SEM with EDS indicates a clear difference in the phase composition and differences in the distribution of the magnetic tau phase and the non-magnetic epsilon-, beta-, and gamma-phases. Magnetic properties also indicate, an improvement in saturation magnetization for the sample exposed to the extra annealing step during synthesis. Our results suggest that an intermediate annealing step in the production of MnAl based alloys will provide a simple way of achieving better phase purity and magnetic properties in the bulk alloy.

  • 18.
    Shtender, Vitalii
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
    Hedlund, Daniel
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Solid State Physics.
    Rosenqvist Larsen, Simon
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
    Svedlindh, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Solid State Physics.
    Sahlberg, Martin
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
    Structural and magnetic properties of new members of the 3:29 phase from the Ce-Fe-Mn system and 1:11 from the Ce-Co-Mn2021In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 855, article id 157435Article in journal (Refereed)
    Abstract [en]

    The Ce–Fe–Mn and Ce–Co–Mn systems have been re-visited with the intent of finding new potential phases for application as permanent magnets. Two new ternary compounds, Ce3(Fe0.638Mn0.362)29 (Nd3(Fe,Ti)29-type, space group P21/c, No. 14, Pearson Symbol mP128) and CeCo8Mn3 (Ce(Ni,Mn)11-type, space group P4/mbm, No. 127, Pearson Symbol tP24) have been discovered in the compositional range where the Ce2(T,Mn)17 (T = Fe, Co) phases are expected to exist with a (H)–Th2Ni17-type structure (space group P63/mmc, No. 194, Pearson Symbol hP38). Detailed investigations of the crystal structures have been performed using X-ray powder diffraction (XRPD) with supporting energy-dispersive X-ray (EDS) analysis. Compositions of the new compounds have been defined based on the EDS analysis as follows: Ce9.7Fe57.5Mn32.8 and Ce9.2Co65.2Mn25.6. A short discussion on the crystal structure peculiarities of the 1:5, 1:11, 1:12, 2:17 and 3:29 compounds in the Ce–T–Mn (T = Fe, Co, Ni, Cu) systems has been made. We present magnetic measurements on selected representatives of the studied phases. The most interesting being the Ce3(Fe0.638Mn0.362)29 phase which has a transition temperature well above room temperature. CeNi4.95Mn6.05 and CeCo8Mn3 exhibits properties characteristic of a canted antiferromagnetic state.

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  • 19.
    Shtender, Vitalii
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry. Univ Paris Est, ICMPE UMR7182, CNRS, UPEC, F-94320 Thiais, France.;NAS Ukraine, Karpenko Phys Mech Inst, 5 Naukova St, UA-79060 Lvov, Ukraine..
    Paul-Boncour, Valerie
    Univ Paris Est, ICMPE UMR7182, CNRS, UPEC, F-94320 Thiais, France..
    Denys, Roman
    HYSTORSYS AS, Box 45, NO-2027 Kjeller, Norway..
    Hedlund, Daniel
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Solid State Physics.
    Svedlindh, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Solid State Physics.
    Zavaliy, Ihor
    NAS Ukraine, Karpenko Phys Mech Inst, 5 Naukova St, UA-79060 Lvov, Ukraine..
    Impact of the R and Mg on the structural, hydrogenation and magnetic properties of R3-xMgxCo9 (R = Pr, Nd, Tb and Y) compounds2022In: Materials research bulletin, ISSN 0025-5408, E-ISSN 1873-4227, Vol. 156, article id 111981Article in journal (Refereed)
    Abstract [en]

    R2MgCo9 (R = Pr, Nd, Tb and Y) compounds have been synthesized by a powder sintering method and the corresponding hydrides have been prepared by a solid gas method. Their crystal structures and magnetic properties have been systematically studied. X-ray diffraction analysis showed that all R2MgCo9 compounds belong to the PuNi3-type structure. The elements Tb, Y, Nd, Pr yield a lowering of the equilibrium pressure which correlates well with the increase in cell volume. The R2MgCo9H(D)x (R = Pr, Nd, Tb and Y; (9.4 <= x <= 12)) hydrides (deuterides) preserve the PuNi3-type structure with hydrogenation-induced volume expansion ranging from 14.7 to 19.6%. The substitution of deuterium for hydrogen in R2MgCo9-(H,D)(2) (R = Tb and Y) prevents fast desorption at room temperature and ambient pressure. As for the magnetic properties, all the studied interme-tallic compounds show ferromagnetic or ferrimagnetic behavior, and in some cases a temperature dependent spin reorientation. Hydrogen insertion reduces the magnetization and decreases the magnetic ordering temperature (TC), whereas Mg for R substitution increases TC.

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  • 20.
    Shtender, Vitalii
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
    Stopfel, Henry
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Solid State Physics.
    Hedlund, Daniel
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Solid State Physics.
    Karlsson, Dennis
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
    Pothala, Rajasekhar
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Skårman, Björn
    Hoganas AB, Bruksgatan 35, S-26383 Hoganas, Sweden..
    Olsson, Fredrik
    Hoganas AB, Bruksgatan 35, S-26383 Hoganas, Sweden..
    Vidarsson, Hilmar
    Höganäs AB, Bruksgatan 35, 263 83, Höganäs, Sweden..
    Andersson, Gabriella
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Svedlindh, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Solid State Physics.
    Sahlberg, Martin
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
    Influence of nano-VC on the structural and magnetic properties of MnAlC-alloy2021In: Scientific Reports, E-ISSN 2045-2322, Vol. 11, article id 14453Article in journal (Refereed)
    Abstract [en]

    Alloys of Mn55Al45C2 with additions of VC nano-particles have been synthesized and their properties evaluated. The Mn55Al45C2(VC)(x) (x=0.25, 0.5 and 1) alloys have been prepared by induction melting resulting in a high content of the ferromagnetic tau -phase (>94 wt.%). Powder X-ray diffraction indicates that nano-VC can be dissolved in the alloy matrix up to 1 at.%. On the other side, metallography investigations by scanning electron microscopy and scanning transmission electron microscope show inclusions of the nanosized additives in the microstructure. The effect of nano-VC on the grain and twin boundaries has been studied by electron backscattering diffraction. The magnetization has been measured by magnetometry up to 9 T while the domain structure has been studied using both magnetic force microscopy as well as Kerr-microscopy. For nano-VC contents above 0.25 at.%, a clear increase of the coercive force is observed, from 57 to 71 kA/m. The optimum appears to be for 0.5 at.% nano-VC which shows a 25% increase in coercive force without losing any saturation magnetization. This independent increase in coercivity is believed to originate from the nano-VC reducing the overall magnetic domain size. Overall, we observe that addition of nano-VC could be an interesting route to increase the coercive force of MnAl, without sacrificing saturation magnetization.

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  • 21.
    Vishina, Alena
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Hedlund, Daniel
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Solid State Physics.
    Shtender, Vitalii
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
    Delczeg-Czirjak, Erna K.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Larsen, Simon R.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
    Vekilova, Olga Yu.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Stockholm Univ, Dept Mat & Environm Chem, S-10691 Stockholm, Sweden.
    Huang, Shuo
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Vitos, Levente
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Royal Inst Technol, Dept Mat Sci & Engn, Appl Mat Phys, SE-10044 Stockholm, Sweden.
    Svedlindh, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Solid State Physics.
    Sahlberg, Martin
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Örebro Univ, Sch Sci & Technol, SE-70182 Örebro, Sweden.
    Herper, Heike C.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Data-driven design of a new class of rare-earth free permanent magnets2021In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 212, article id 116913Article in journal (Refereed)
    Abstract [en]

    A new class of rare-earth-free permanent magnets is proposed. The parent compound of this class is Co3Mn2Ge, and its discovery is the result of first principles theory combined with experimental synthesis and characterisation. The theory is based on a high-throughput/data-mining search among materials listed in the ICSD database. From ab-initio theory of the defect free material it is predicted that the saturation magnetization is 1.71 T, the uniaxial magnetocrystalline anisotropy is 1.44 MJ/m3, and the Curie temperature is 700 K. Co3Mn2Ge samples were then synthesized and characterised with respect to structure and magnetism. The crystal structure was found to be the MgZn2-type, with partial disorder of Co and Ge on the crystallographic lattice sites. From magnetization measurements a saturation polarization of 0.86 T at 10 K was detected, together with a uniaxial magnetocrystalline anisotropy constant of 1.18 MJ/m3, and the Curie temperature of TC = 359 K. These magnetic properties make Co3Mn2Ge a very promising material as a rare-earth free permanent magnet, and since we can demonstrate that magnetism depends critically on the amount of disorder of the Co and Ge atoms, a further improvement of the magnetism is possible. We demonstrate here that the class of compounds based on T3Mn2X (T = Co or alloys between Fe and Ni; X = Ge, Al or Ga) in the MgZn2 structure type, form a new class of rare-earth free permanent magnets with very promising performance.

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  • 22.
    Werwinski, Miroslaw
    et al.
    Polish Acad Sci, Inst Mol Phys, M Smoluchowskiego 17, PL-60179 Poznan, Poland.
    Edstroem, Alexander
    Swiss Fed Inst Technol, Mat Theory, Wolfgang Pauli Str 27, CH-8093 Zurich, Switzerland.
    Rusz, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Hedlund, Daniel
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Gunnarsson, Klas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Svedlindh, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Cedervall, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
    Sahlberg, Martin
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
    Magnetocrystalline anisotropy of Fe5PB2 and its alloys with Co and 5d elements: A combined first-principles and experimental study2018In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 98, no 21, article id 214431Article in journal (Refereed)
    Abstract [en]

    The Fe5PB2 compound offers tunable magnetic properties via the possibility of various combinations of substitutions on the Fe and P sites. Here, we present a combined computational and experimental study of the magnetic properties of (Fe1-xCox)(5)PB2. Computationally, we are able to explore the full concentration range, while the real samples were only obtained for 0 <= x <= 0.7. The calculated magnetic moments, Curie temperatures, and magnetocrystalline anisotropy energies (MAEs) are found to decrease with increasing Co concentration. Co substitution allows for tuning the Curie temperature in a wide range of values, from about six hundred to zero kelvins. As the MAE depends on the electronic structure in the vicinity of the Fermi energy, the geometry of the Fermi surface of Fe5PB2 and the k-resolved contributions to the MAE are discussed. Low-temperature measurements of an effective anisotropy constant for a series of (Fe1-xCox)(5)PB2 samples determined the highest value of 0.94 MJ m(-3) for the terminal Fe5PB2 composition, which then decreases with increasing Co concentration, thus confirming the computational result that Co alloying of Fe5PB2 is not a good strategy to increase the MAE of the system. However, the relativistic version of the fixed spin moment method reveals that a reduction in the magnetic moment of Fe5PB2, by about 25%, produces a fourfold increase of the MAE. Furthermore, calculations for (Fe0.95X0.05)(5)PB2 (X = 5d element) indicate that 5% doping of Fe5PB2 with W or Re should double the MAE. These are results of high interest for, e.g., permanent magnet applications, where a large MAE is crucial.

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