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Marathe, M. & Herper, H. C. (2023). Exploration of all-3d Heusler alloys for permanent magnets: An ab initio based high-throughput study. Physical Review B, 107(17), Article ID 174402.
Open this publication in new window or tab >>Exploration of all-3d Heusler alloys for permanent magnets: An ab initio based high-throughput study
2023 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 107, no 17, article id 174402Article in journal (Refereed) Published
Abstract [en]

Heusler alloys have attracted interest in various fields of functional materials since their properties can quite easily be tuned by composition. Here, we have investigated the relatively new class of all-3d Heusler alloys in view of their potential as permanent magnets. To identify suitable candidates, we performed a high-throughput study using an electronic structure database to search for X2Y Z-type Heusler systems with tetragonal symmetry and high magnetization. For the alloys which passed our selection filters, we have used a combination of density functional theory calculations and spin dynamics modeling to investigate their magnetic properties including the magnetocrystalline anisotropy energy and exchange interactions. The candidates which fulfilled all the search criteria served as input for the investigation of the temperature dependence of the magnetization and determination of the Curie temperature. Based on our results, we suggest that Fe2NiZn, Fe2NiTi, and Ni2CoFe are potential candidates for permanent magnets with large out-of-plane magnetic anisotropy (1.23, 0.97, and 0.82 MJ/m3, respectively) and high Curie temperatures lying more than 200 K above the room temperature. We further show that the magnitude and direction of anisotropy are very sensitive to the strain by calculating the values of anisotropy energy for several tetragonal phases. Thus application of strain can be used to tune the anisotropy in these compounds.

Place, publisher, year, edition, pages
American Physical Society, 2023
National Category
Condensed Matter Physics Other Physics Topics
Identifiers
urn:nbn:se:uu:diva-502505 (URN)10.1103/PhysRevB.107.174402 (DOI)000986252200002 ()
Funder
StandUpSwedish Foundation for Strategic Research, EM16-0039EU, European Research CouncilSwedish National Infrastructure for Computing (SNIC)Olle Engkvists stiftelseeSSENCE - An eScience Collaboration
Available from: 2023-05-29 Created: 2023-05-29 Last updated: 2023-05-29Bibliographically approved
Vishina, A., Eriksson, O. & Herper, H. C. (2023). Fe2C- and Mn-2(W/Mo)B-4-based rare-earth-free permanent magnets as a result of the high-throughput and data-mining search. Materials Research Letters, 11(1), 76-83
Open this publication in new window or tab >>Fe2C- and Mn-2(W/Mo)B-4-based rare-earth-free permanent magnets as a result of the high-throughput and data-mining search
2023 (English)In: Materials Research Letters, E-ISSN 2166-3831, Vol. 11, no 1, p. 76-83Article in journal (Refereed) Published
Abstract [en]

A high-throughput and data-mining search for rare-earth-free permanent magnets is reported for materials containing a 3d and p-element of the Periodic Table. Three of the most promising compounds, Fe 2 C, Mn2MoB4 , and Mn2WB4, were investigated in detail by ab initio electronic structure theory coupled to atomistic spin-dynamics. For these systems doping protocols were also investigated and, in particular, (Fe0.75X0.25)(2) C (X = Mn, Cr, V, and Ti), Mn2XB4 (X = Mo and W) along with Mn 2 (X0.5Y0.5)B-4 (X,Y = Mo, W, Ta, Cr) are suggested here as promising candidates for applications as permanent magnets.

Place, publisher, year, edition, pages
Taylor & Francis, 2023
Keywords
Permanent magnet, rare-earth-free, high-throughput, data-mining, DFT
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-486394 (URN)10.1080/21663831.2022.2117576 (DOI)000857146100001 ()
Funder
Swedish Research Council, 2018-05973Swedish National Infrastructure for Computing (SNIC), SNIC 2022/5-338Swedish National Infrastructure for Computing (SNIC), SNIC 2021/136Swedish National Infrastructure for Computing (SNIC), SNIC2021/5-340Knut and Alice Wallenberg FoundationeSSENCE - An eScience CollaborationStandUpEU, European Research Council
Available from: 2022-10-10 Created: 2022-10-10 Last updated: 2024-02-23Bibliographically approved
Ghorai, S., Vieira, R. M., Shtender, V., Delczeg-Czirjak, E. K., Herper, H. C., Björkman, T., . . . Svedlindh, P. (2023). Giant magnetocaloric effect in the (Mn,Fe)NiSi-system.
Open this publication in new window or tab >>Giant magnetocaloric effect in the (Mn,Fe)NiSi-system
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2023 (English)Manuscript (preprint) (Other academic)
Abstract [en]

The search for energy-efficient and environmentally friendly cooling technologies is a key driver for the development of magnetic refrigeration based on the magnetocaloric effect (MCE). This phenomenon arises from the interplay between magnetic and lattice degrees of freedom that is strong in certain materials, leading to a change in temperature upon application or removal of a magnetic field. Here we report on a new material, Mn1−xFexNiSi0.95Al0.05, with an exceptionally large isothermal entropy at room temperature. By combining experimental and theoretical methods we outline the microscopic mechanism behind the large MCE in this material. It is demonstrated that the competition between the Ni2In-type hexagonal phase and the MnNiSi-type orthorhombic phase, that coexist in this system, combined with the distinctly different magnetic properties of these phases, is a key parameter for the functionality of this material for magnetic cooling.

National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-525213 (URN)10.48550/arXiv.2307.00128 (DOI)
Available from: 2024-03-19 Created: 2024-03-19 Last updated: 2024-03-19
Herper, H. C., Skokov, K. P., Ener, S., Thunström, P., Diop, L. V. B., Gutfleisch, O. & Eriksson, O. (2023). Magnetic properties of NdFe11Ti and YFe11Ti, from experiment and theory. Acta Materialia, 242, Article ID 118473.
Open this publication in new window or tab >>Magnetic properties of NdFe11Ti and YFe11Ti, from experiment and theory
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2023 (English)In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 242, article id 118473Article in journal (Refereed) Published
Abstract [en]

NdFe11Ti and YFe11Ti serve as prototypes for rare-earth (RE) lean or REfree magnets with the ThMn12-type structure. Although NdFe11Ti has been studied for a long time the origin of its complex magnetism at low temperature is so far not well-understood. We present a comprehensive theoretical and experimental study of the magnetic properties of NdFe11Ti and RE-free YFe11Ti to elucidate the influence of the 4f electrons. The partially localized 4 f electrons of Nd are the driving force behind the complex behavior of the magnetocrystalline anisotropy which changes from cone to uniaxial above 170 dK. The spontaneous magnetization and the five leading anisotropy constants were determined from high-quality single crystal samples over a wide temperature range using field dependencies of magnetization measured along the principle crystallographic directions. The experimental data are compared with density functional theory combined with a Hartree-Fock correction (+U) and an approximate dynamical mean-field theory.

Place, publisher, year, edition, pages
Elsevier, 2023
Keywords
Permanent magnets, Rare-earths, Anisotropy, Magnetism, DFT, DMFT
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-495864 (URN)10.1016/j.actamat.2022.118473 (DOI)000908332400005 ()
Funder
EU, Horizon 2020, EU 686056Swedish Foundation for Strategic Research, EM16-0 039Swedish Energy AgencySwedish Research Council
Available from: 2023-02-08 Created: 2023-02-08 Last updated: 2023-02-08Bibliographically approved
Vishina, A., Eriksson, O. & Herper, H. C. (2023). Stable and metastable rare-earth-free permanent magnets from a database of predicted crystal structures. Acta Materialia, 261, Article ID 119348.
Open this publication in new window or tab >>Stable and metastable rare-earth-free permanent magnets from a database of predicted crystal structures
2023 (English)In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 261, article id 119348Article in journal (Refereed) Published
Abstract [en]

With the recent developments in crystal structure prediction, databases of new (not previously synthesized) materials are being created. One of these databases contains more than a million entries with the distance to the Convex Hull predicted by crystal-graph attention networks. Hence, stable and metastable materials can be extracted and then investigated for any desired properties. A high-throughput and data-mining approach we previously developed to search for rare-earth-free permanent magnets was applied to these compounds. As a result, four promising candidates for novel rare-earth-free permanent magnets were discovered with high magnetization, high uniaxial magnetocrystalline anisotropy, and high Curie temperature - Ta3ZnFe8, AlFe2, Co3Ni2, and Fe3Ge. The materials were investigated in more detail and all were verified to be dynamically stable.

Place, publisher, year, edition, pages
Elsevier, 2023
Keywords
Permanent magnets, Rare-earth-free, High-throughput, DFT, Neural networks, Structure prediction
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-518456 (URN)10.1016/j.actamat.2023.119348 (DOI)001088649500001 ()
Funder
Swedish Foundation for Strategic ResearchSwedish Research CouncilSwedish Energy AgencyKnut and Alice Wallenberg FoundationStandUpEU, European Research Council, 854843Swedish Research Council, 2018-05973Swedish National Infrastructure for Computing (SNIC), SNIC 2021/5-340
Available from: 2023-12-20 Created: 2023-12-20 Last updated: 2023-12-20Bibliographically approved
Vieira Martinho, R., Eriksson, O., Björkman, T., Šipr, O. & Herper, H. C. (2023). The role of pressure-induced stacking faults on the magnetic properties of gadolinium.
Open this publication in new window or tab >>The role of pressure-induced stacking faults on the magnetic properties of gadolinium
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2023 (English)Manuscript (preprint) (Other academic)
Abstract [en]

Experimental data show that under pressure, Gd goes through a series of structural transitions hcp → Sm-type (close-packed rhombohedral)→ dhcp that is accompanied by a gradual decrease of the Curie temperature and magnetization till the collapse of a finite magnetization close to the dhcp structure. We explore theoretically the pressure-induced changes of the magnetic properties, by describing these structural transitions as the formation of fcc stackings faults. Using this approach, we are able to describe correctly the variation of the Curie temperature with pressure, in contrast to a static structural model using the hcp structure. 

National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-525212 (URN)10.48550/arXiv.2309.01285 (DOI)
Available from: 2024-03-19 Created: 2024-03-19 Last updated: 2024-03-20
Vieira, R. M., Eriksson, O., Bjorkman, T., Bergman, A. & Herper, H. C. (2022). Realistic first-principles calculations of the magnetocaloric effect: applications to hcp Gd. Materials Research Letters, 10(3), 156-162
Open this publication in new window or tab >>Realistic first-principles calculations of the magnetocaloric effect: applications to hcp Gd
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2022 (English)In: Materials Research Letters, E-ISSN 2166-3831, Vol. 10, no 3, p. 156-162Article in journal (Refereed) Published
Abstract [en]

We present an efficient computational approach to evaluate field-dependent entropy of magnetocaloric materials from ab-initio methods. The temperature dependence is reported for the entropy change, specific heat and magnetization for hcp Gd. To obtain optimal accuracy in the calculations, a mixed-scheme for magnetic Monte Carlo simulations is proposed and found to be superior to using pure quantum or classic statistics. It is demonstrated that lattice and magnetic contributions play a role in the entropy change and that the dominating contribution comes from the magnetic contribution. The total calculated entropy change agrees with measurements at room temperature. IMPACT STATEMENT Demonstration of the accuracy of ab-initio theory, coupled to statistical methods, for accurate calculations of the total entropy variation associated with the magnetic transition of Gd. Reproduction of experimental data of entropy change.

Place, publisher, year, edition, pages
Taylor & Francis, 2022
Keywords
Magnetocaloric, Gd, entropy, Monte Carlo, mixed statistics
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-467898 (URN)10.1080/21663831.2022.2033866 (DOI)000752058000001 ()
Funder
Swedish Foundation for Strategic Research, EM16-0039Swedish Energy AgencySwedish Research CouncilSwedish Research Council, 2018-05973StandUp
Available from: 2022-02-18 Created: 2022-02-18 Last updated: 2024-03-19Bibliographically approved
Larsen, S. R., Shtender, V., Hedlund, D., Delczeg-Czirjak, E. K., Beran, P., Cedervall, J., . . . Sahlberg, M. (2022). Revealing the Magnetic Structure and Properties of Mn(Co,Ge)2. Inorganic Chemistry, 61(44), 17673-17681
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
Schröter, M., Herper, H. C. & Grünebohm, A. (2022). Tuning the magnetic phase diagram of Ni-Mn-Ga by Cr and Co substitution. Journal of Physics D: Applied Physics, 55(2), Article ID 025002.
Open this publication in new window or tab >>Tuning the magnetic phase diagram of Ni-Mn-Ga by Cr and Co substitution
2022 (English)In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 55, no 2, article id 025002Article in journal (Refereed) Published
Abstract [en]

Ni-Mn-based Heusler alloys have a high technical potential related to a large change of magnetization at the structural phase transition. These alloys show a subtle dependence of magnetic properties and structural phase stability on composition and substitution by 3d elements and although they have been extensively investigated, there are still ambiguities in the published results and their interpretation. To shed light on the large spread of reported properties, we perform a comprehensive study by means of density functional theory calculations. We focus on Cr and Co co-substitution whose benefit has been predicted previously for the expensive Ni-Mn-In-based alloy and study the more abundant iso-electronic counterpart Ni-Mn-Ga. We observe that substituting Ni partially by Co and/or Cr enhances the magnetization of the Heusler alloy and at the same time reduces the structural transition temperature. Thereby, Cr turns out to be more efficient to stabilize the ferromagnetic alignment of the Mn spins by strong antiferromagnetic interactions between Mn and Cr atoms. In a second step, we study Cr on the other sublattices and observe that an increase in the structural transition temperature is possible, but depends critically on the short-range order of Mn and Cr atoms. Based on our results, we are able to estimate composition dependent magnetic phase diagrams. In particular, we demonstrate that neither the atomic configuration with the lowest energy nor the results based on the coherent potential approximation are representative for materials with a homogeneous distribution of atoms and we also predict a simple method for fast screening of different concentrations which can be viewed as a blueprint for the study of high entropy alloys. Our results help to explain the large variation of experimentally found materials properties.

Place, publisher, year, edition, pages
IOP Publishing Ltd, 2022
Keywords
Heusler alloys, magnetic phases, magnetocaloric, density functional theory, Mn
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-458248 (URN)10.1088/1361-6463/ac2a66 (DOI)000707215000001 ()
Funder
Swedish Foundation for Strategic Research eSSENCE - An eScience CollaborationStandUpSwedish Research Council
Available from: 2021-11-11 Created: 2021-11-11 Last updated: 2021-11-11Bibliographically approved
Vishina, A., Eriksson, O., Vekilova, O. Y., Bergman, A. & Herper, H. C. (2021). Ab-initio study of the electronic structure and magnetic properties of Ce2Fe17. Journal of Alloys and Compounds, 888, Article ID 161521.
Open this publication in new window or tab >>Ab-initio study of the electronic structure and magnetic properties of Ce2Fe17
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2021 (English)In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 888, article id 161521Article in journal (Refereed) Published
Abstract [en]

The Ce2Fe17 intermetallic compound has been studied intensely for several decades; its low-temperature state is reported experimentally either as ferromagnetic or antiferromagnetic by different authors, with a measured ordering temperature ranging within a hundred Kelvin. The existing theoretical investigations overestimate the experimental total magnetic moment of Ce2Fe17 by 20-40% and predict a ferromagnetic ground state. By means of first-principle electronic structure calculations, we show that the total magnetic moment of Ce2Fe17 can be reproduced within the Local Density Approximation while functionals based on the Generalized Gradient Approximation fail. Atomistic spin dynamics simulations are shown to capture the change in the magnetic state of Ce2Fe17 with temperature, and closely replicate the reported helical structure that appears in some of the experimental investigations.

Place, publisher, year, edition, pages
ElsevierElsevier BV, 2021
Keywords
Permanent magnets, Rare earth alloys and compounds, Cerium, Magnetism, Spin dynamics, Computer simulations
National Category
Metallurgy and Metallic Materials Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-457951 (URN)10.1016/j.jallcom.2021.161521 (DOI)000704757000004 ()
Funder
Swedish Foundation for Strategic Research , EM16-0 039Swedish Energy AgencySwedish Research CouncilKnut and Alice Wallenberg FoundationEU, European Research Council, 854843Swedish National Infrastructure for Computing (SNIC), 2020/8-34Swedish National Infrastructure for Computing (SNIC), 2020/1-20Vinnova
Available from: 2021-11-08 Created: 2021-11-08 Last updated: 2024-01-15Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0001-6159-1244

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