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Strategies for finding new magnetic materials
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry. Uppsala universitet.
2022 (English)Doctoral thesis, comprehensive summary (Other academic)
Description
Abstract [en]

Magnetic materials are indispensable in modern day society. The vast majority of energy generation and conversion involves some kind of magnetic material, and several other applications such as data storage also use them. Despite this there are relatively few types of magnetic materials in use today, which is due to the difficulty of finding new materials that have the necessary properties. In this thesis synthesis of new magnetic materials is performed using a variety oftechniques in an attempt to identify a structured approach to finding crystal structures suited for further development.

Three approaches for developing new magnetic materials were used. Targeted substitutions of Mn was done in AlCoCrFeMnxNi and Mn3Co20B6, where Mn provided significant contributions to the magnetic moment, at the cost of stability of the ferromagnetic structures. A new system was identified using theoretical screening, Mn2Co3Ge, which was successfully synthesised. Application of the substitution method revealed properties in the system favourable for magnetic refrigeration. New systems were also discovered in synthesis attempts of Mn2Co3Ge and Ce-based magnets, but these materials were ferrimagnetic, or canted anti-ferromagnetic, resulting in low magnetisation.

Varying degrees of success were seen in creating magnetic materials with these approaches. Theoretical screening is likely to become an incredibly powerful tool in the future as more understanding of systems is gained. Complementing the theoretical screening method with the newly discovered structures could be a promising avenue for developing new applicable materials. Substitution of elements will remain an extremely powerful tool for tuning properties and by combining it with theoretical screening will likely be key to discovering new applicable magnet systems in the future.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2022. , p. 59
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 2198
Keywords [en]
Magnetic materials, Materials development, Alloys
National Category
Materials Chemistry
Research subject
Chemistry with specialization in Materials Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-486285ISBN: 978-91-513-1617-8 (print)OAI: oai:DiVA.org:uu-486285DiVA, id: diva2:1701628
Public defence
2022-11-24, Polhemsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:15 (English)
Opponent
Supervisors
Available from: 2022-11-02 Created: 2022-10-06 Last updated: 2022-11-02
List of papers
1. Magnetic properties and thermal stability of B2 and bcc phases in AlCoCrFeMnxNi
Open this publication in new window or tab >>Magnetic properties and thermal stability of B2 and bcc phases in AlCoCrFeMnxNi
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2021 (English)In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 861, article id 158450Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Elsevier, 2021
Keywords
High entropy alloys, X-ray diffraction, Phase transitions, Magnetism
National Category
Metallurgy and Metallic Materials Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-438737 (URN)10.1016/j.jallcom.2020.158450 (DOI)000619199300073 ()
Funder
Swedish Foundation for Strategic Research , EM-16-0039Swedish Energy AgencySwedish Research CouncilSweGRIDS - Swedish Centre for Smart Grids and Energy Storage
Available from: 2021-03-29 Created: 2021-03-29 Last updated: 2024-01-15Bibliographically approved
2. Magnetism and magnetic structure determination of a selected (Mn,Co)(23)B-6-compound
Open this publication in new window or tab >>Magnetism and magnetic structure determination of a selected (Mn,Co)(23)B-6-compound
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2022 (English)In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 905, article id 164225Article in journal (Refereed) Published
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

Place, publisher, year, edition, pages
ElsevierElsevier BV, 2022
Keywords
Magnetism, X-ray diffraction, Neutron diffraction, First principles calculations
National Category
Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-473658 (URN)10.1016/j.jallcom.2022.164225 (DOI)000779903700003 ()
Funder
Swedish Research CouncilSwedish Foundation for Strategic Research , EM-16-0 039StandUp
Available from: 2022-05-02 Created: 2022-05-02 Last updated: 2024-01-15Bibliographically approved
3. 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
4. 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
5. 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
6. Variants of the X-phase in the Mn-Co-Ge system
Open this publication in new window or tab >>Variants of the X-phase in the Mn-Co-Ge system
2021 (English)In: ACTA CRYSTALLOGRAPHICA SECTION C-STRUCTURAL CHEMISTRY, ISSN 2053-2296, Vol. 77, p. 176-180Article in journal (Refereed) Published
Abstract [en]

We report two new variants of the X-phase (orthorhombic, space group Pnnm) derived from the Mn-Co-Ge system. Two compositionally related crystals were investigated by means of single-crystal X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS). The Mn14.9Co15.5Ge6.6 and Mn14Co16.2Ge6.8 intermetallic compounds are part of the homogeneity region of the X-phase and adopt the Mn-14(Mn0.11Co0.64Si0.25)(23) structure type. The composition obtained from refinement of the XRD data is in agreement with the EDS results. In the present study, chemical disorder was only detected on the 8h positions. The ordering is compared with other members of the X-phase family and shows that the degree of disordering depends on the chemical composition. No completely ordered variants of the X-phase have yet been reported.

Place, publisher, year, edition, pages
International Union Of CrystallographyINT UNION CRYSTALLOGRAPHY, 2021
Keywords
intermetallic compound, crystal structure, X-phase, Mn-Co-Ge system, manganese, cobalt, germanide
National Category
Inorganic Chemistry Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-442589 (URN)10.1107/S2053229621002370 (DOI)000637723900003 ()33818439 (PubMedID)
Funder
Swedish Foundation for Strategic Research , EM16-0039
Available from: 2021-05-24 Created: 2021-05-24 Last updated: 2024-01-15Bibliographically approved
7. 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
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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

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