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Gunnarsson, K
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Publications (10 of 54) Show all publications
Legaria, E. P., Saldan, I., Svedlindh, P., Wetterskog, E., Gunnarsson, K., Kessler, V. G. & Seisenbaeva, G. A. (2018). Coordination of rare earth element cations on the surface of silica-derived nanoadsorbents. Dalton Transactions, 47(4), 1312-1320
Open this publication in new window or tab >>Coordination of rare earth element cations on the surface of silica-derived nanoadsorbents
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2018 (English)In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 47, no 4, p. 1312-1320Article in journal (Refereed) Published
Abstract [en]

Silica (SiO2)-derived nanoadsorbents are a powerful and attractive tool for the extraction and separation of rare earth elements (REE) from many perspectives such as reusability, efficiency and minimum impact on the environment. In the present work, we investigated two different methods of adsorption down to the molecular level: (1) the mechanism of the coordination of different groups of REE (light, medium, heavy) with iminodiacetic acid (IDA) was revealed by exploiting models obtained from X-ray crystallography, explaining the selectivity of this type of ligand, and (2) the mechanism of the seeding of RE(OH)(3) initiated by SiO2-based nanoadsorbents was investigated by EXAFS, both individually and in combination with mechanism (1), showing the coexistence of both mechanisms. The REE loaded nanoadsorbents possess a high magnetic susceptibility. This property was studied by magnetometry to quantify the REE adsorption efficiency and compared with the values obtained from complexometry.

Place, publisher, year, edition, pages
ROYAL SOC CHEMISTRY, 2018
National Category
Chemical Sciences Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-346224 (URN)10.1039/c7dt04388k (DOI)000423465200036 ()29300064 (PubMedID)
Funder
EU, FP7, Seventh Framework Programme, 309373
Available from: 2018-03-15 Created: 2018-03-15 Last updated: 2018-03-28Bibliographically approved
Cedervall, J., Nonnet, E., Hedlund, D., Häggström, L., Ericsson, T., Werwinski, M., . . . Sahlberg, M. (2018). Influence of cobalt substitution on the magnetic properties of Fe5PB2. Inorganic Chemistry, 57(2), 777-784
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: 2018-10-19Bibliographically approved
Keshavarz, S., Kontos, S., Wardecki, D., Kvashnin, Y., Pereiro, M., Panda, S. K., . . . Svedlindh, P. (2018). Magnetic properties of Ruddlesden-Popper phases Sr3-&: A combined experimental and theoretical investigation. Physical Review Materials, 2(4), Article ID 044005.
Open this publication in new window or tab >>Magnetic properties of Ruddlesden-Popper phases Sr3-&: A combined experimental and theoretical investigation
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2018 (English)In: Physical Review Materials, ISSN 2475-9953, Vol. 2, no 4, article id 044005Article in journal (Refereed) Published
Abstract [en]

We present a comprehensive study of the magnetic properties of Sr3-xYx(Fe1.25Ni0.75)O-7(-delta )(0 <= x <= 0.75). Experimentally, the magnetic properties are investigated using superconducting quantum interference device (SQUID) magnetometry and neutron powder diffraction (NPD). This is complemented by a theoretical study based on density functional theory as well as the Heisenberg exchange parameters. Experimental results show an increase in the Ned temperature (T-N) with an increase of Y concentrations and O occupancy. The NPD data reveal that all samples are antiferromagnetically ordered at low temperatures, which has been confirmed by our theoretical simulations for the selected samples. Our first-principles calculations suggest that the three-dimensional magnetic order is stabilized due to finite interlayer exchange couplings. The latter give rise to finite interlayer spin-spin correlations, which disappear above T-N.

National Category
Condensed Matter Physics Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-354116 (URN)10.1103/PhysRevMaterials.2.044005 (DOI)000430385300001 ()
Funder
Swedish Research CouncilKnut and Alice Wallenberg Foundation
Available from: 2018-06-19 Created: 2018-06-19 Last updated: 2018-08-24Bibliographically approved
Shafeie, S., Fang, H., Hedlund, D., Nyberg, A., Svedlindh, P., Gunnarsson, K. & Sahlberg, M. (2018). One step towards MnAl-based permanent magnets  - Differences in magnetic, and microstructural properties from an intermediate annealing step during synthesis. Journal of Alloys and Compounds
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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2018 (English)In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669Article in journal (Refereed) Submitted
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
Natural Sciences Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-368283 (URN)
Available from: 2018-12-03 Created: 2018-12-03 Last updated: 2018-12-06Bibliographically approved
Fang, H., Cedervall, J., Hedlund, D., Shafeie, S., Deledda, S., Olsson, F., . . . Sahlberg, M. (2018). Structural, microstructural and magnetic evolution in cryo milled carbon doped MnAl. Scientific Reports, 8(1), Article ID 2525.
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, ISSN 2045-2322, 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: 2018-04-17Bibliographically approved
Hedlund, D., Cedervall, J., Edström, A., Werwinski, M., Kontos, S., Eriksson, O., . . . Gunnarsson, K. (2017). Magnetic properties of the Fe5SiB2−Fe5PB2 system. Physical Review B, 96(9), Article ID 094433.
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: 2017-12-20Bibliographically approved
Fang, H., Kontos, S., Ångstrom, J., Cedervall, J., Svedlindh, P., Gunnarsson, K. & Sahlberg, M. (2016). Directly obtained tau-phase MnAl, a high performance magnetic material for permanent magnets. Journal of Solid State Chemistry, 237, 300-306
Open this publication in new window or tab >>Directly obtained tau-phase MnAl, a high performance magnetic material for permanent magnets
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2016 (English)In: Journal of Solid State Chemistry, ISSN 0022-4596, E-ISSN 1095-726X, Vol. 237, p. 300-306Article in journal (Refereed) Published
Abstract [en]

The metastable tetragonal iota-phase has been directly obtained from casting Mn0.54Al0.46 and (Mn0.55Al0.45)(100)C-2 using the drop synthesis method. The as-casted samples were ball milled to decrease the particle size and relaxed at 500 degrees C for 1 h. The phase composition, crystallographic parameters, magnetic properties and microstructure were systematically studied. The results reveal that the iota-phase could be directly obtained from drop synthesis. The highest M-s of 117 emu/g was achieved in the (Mn0.55Al0.45)(100)C-2 where the iota-phase was stabilized by doping with carbon. Carbon doping increased the c/a ratio of the tau-phase as it occupies specific interstitial positions (1/2, 1/2, 0) in the structure. Furthermore, ball milling increases the coercivity (H-c) at the expense of a decrease in magnetic saturation (M-s). The increase in coercivity is explained by a decrease of grain size in conjunction with domain wall pinning due to defects introduced during the ball milling process.

Keywords
Permanent magnets, Rare-earth free, High temperature synthesis, Diffraction, Magnetic measurements
National Category
Chemical Sciences Physical Sciences Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-294651 (URN)10.1016/j.jssc.2016.02.031 (DOI)000373661100041 ()
Funder
Swedish Energy AgencySweGRIDS - Swedish Centre for Smart Grids and Energy Storage
Available from: 2016-06-02 Created: 2016-05-26 Last updated: 2017-11-30Bibliographically approved
Werwinski, M., Kontos, S., Gunnarsson, K., Svedlindh, P., Cedervall, J., Höglin, V., . . . Rusz, J. (2016). Magnetic properties of Fe5SiB2 and its alloys with P, S, and Co. PHYSICAL REVIEW B, 93(17), Article ID 174412.
Open this publication in new window or tab >>Magnetic properties of Fe5SiB2 and its alloys with P, S, and Co
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2016 (English)In: PHYSICAL REVIEW B, ISSN 2469-9950, Vol. 93, no 17, article id 174412Article in journal (Refereed) Published
Abstract [en]

Fe5SiB2 has been synthesized and magnetic measurements have been carried out, revealing that M-sat = 0.92 MA/mat T = 300 K. The M versus T curve shows a broad peak around T = 160 K. The anisotropy constant K-1, estimated at T = 300 K, is 0.25 MJ/m(3). Theoretical analysis of Fe5SiB2 system has been carried out and extended to the full range of Fe5Si1-xPxB2, Fe5P1-xSxB2, and (Fe1-xCox)(5)SiB2 compositions. The electronic band structures have been calculated using the full-potential local-orbital minimum-basis scheme (FPLO-14). The calculated total magnetic moments are 9.20, 9.15, 9.59, and 2.42 mu(B) per formula units of Fe5SiB2, Fe5PB2, Fe5SB2, and Co5SiB2, respectively. In agreement with experiment, magnetocrystalline anisotropy energies (MAE's) calculated for T = 0 K change from a negative (easy-plane) anisotropy -0.28 MJ/m(3) for Fe5SiB2 to the positive (easy-axis) anisotropy 0.35 MJ/m(3) for Fe5PB2. Further increase of the number of p electrons in Fe5P1-xSxB2 leads to an increase of MAE up to 0.77 MJ/m(3) for the hypothetical Fe5P0.4S0.6B2 composition. Volume variation and fixed spin moment calculations (FSM) performed for Fe5SiB2 show an inverse relation between MAE and magnetic moment in the region down to about 15% reduction of the spin moment. The alloying of Fe5SiB2 with Co is proposed as a practical realization of magnetic moment reduction, which ought to increase MAE. MAE calculated in virtual crystal approximation (VCA) for a full range of (Fe1-xCox)(5)SiB2 compositions reaches the maximum value of 1.16 MJ/m(3) at Co concentration x = 0.3, with the magnetic moment 7.75 mu(B) per formula unit. Thus, (Fe0.7Co0.3)(5)SiB2 is suggested as a candidate for a rare-earth free permanent magnet. For the stoichiometric Co5SiB2 there is an easy-plane magnetization, with the value of MAE = -0.15 MJ/m(3).

National Category
Physical Sciences Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-298092 (URN)10.1103/PhysRevB.93.174412 (DOI)000376244900004 ()
Funder
Göran Gustafsson Foundation for Research in Natural Sciences and MedicineSwedish Research CouncilEU, FP7, Seventh Framework Programme
Available from: 2016-06-29 Created: 2016-06-29 Last updated: 2017-01-25Bibliographically approved
Cedervall, J., Kontos, S., Hansen, T. C., Balmes, O., Martinez-Casado, F. J., Matej, Z., . . . Sahlberg, M. (2016). Magnetostructural transition in Fe5SiB2 observed with neutron diffraction. Journal of Solid State Chemistry, 235, 113-118
Open this publication in new window or tab >>Magnetostructural transition in Fe5SiB2 observed with neutron diffraction
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2016 (English)In: Journal of Solid State Chemistry, ISSN 0022-4596, E-ISSN 1095-726X, Vol. 235, p. 113-118Article in journal (Refereed) Published
Abstract [en]

The crystal and magnetic structure of Fe5SiB2 has been studied by a combination of X-ray and neutron diffraction. Also, the magnetocrystalline anisotropy energy constant has been estimated from magnetisation measurements. High quality samples have been prepared using high temperature synthesis and subsequent heat treatment protocols. The crystal structure is tetragonal within the space group I4/mcm and the compound behaves ferromagnetically with a Curie temperature of 760 K. At 172 K a spin reorientation occurs in the compound and the magnetic moments go from aligning along the c-axis (high T) down to the ab-plane (low T). The magnetocrystalline anisotropy energy constant has been estimated to 03 MJ/m(3) at 300 K.

National Category
Inorganic Chemistry Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-267572 (URN)10.1016/j.jssc.2015.12.016 (DOI)000370467900017 ()
Funder
Swedish Research Council
Available from: 2015-11-24 Created: 2015-11-24 Last updated: 2017-12-01Bibliographically approved
Strömberg, M., Göransson, J., Gunnarsson, K., Nilsson, M., Svedlindh, P. & Strømme, M. (2015). Magnetic detection of small entities. European Patent Organisation 08807710.2.
Open this publication in new window or tab >>Magnetic detection of small entities
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2015 (English)Patent (Other (popular science, discussion, etc.))
National Category
Nano Technology
Research subject
Engineering Science with specialization in Nanotechnology and Functional Materials
Identifiers
urn:nbn:se:uu:diva-264724 (URN)
Patent
European Patent Organisation 08807710.2 (2015-05-04)
Available from: 2015-10-15 Created: 2015-10-15 Last updated: 2016-11-30
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