Abstract
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.
Highlights
Rare earth (RE) permanent magnets dominate the market where high-performance magnetic materials are needed - areas such as green-energy generation, including wind and wave power, electric vehicle motors and generators, and many more
Vienna Ab Initio Simulation Package (VASP) was used for structure relaxation at the posthigh-throughput stage as well as to calculate spin-orbit coupling energies, for the analysis presented in the Appendix
The reason for using less strict criteria, is not to miss new classes of compounds, that have the potential to become technologically relevant, after e.g alloying or structural refinements. Using these criteria we have identified the following compounds as potential new permanent magnets: ScFe4P2, Co3Mn2Ge, Mn3V2Si3, ScMnSi, and Cu2Fe4S7 and we report in Table 1 their calculated saturation magnetization, magnetic anisotropy energy (MAE), and magnetic hardness
Summary
Rare earth (RE) permanent magnets dominate the market where high-performance magnetic materials are needed - areas such as green-energy generation, including wind and wave power, electric vehicle motors and generators, and many more. The heavier rare-earth elements which are necessary for obtaining the good magnetic characteristics of these materials (such as Pr, Nd, Sm, Tb, or Dy) [1], can only be mined with methods that leave an environmental footprint, are quite expensive, and are rapidly decreasing in availability. Green technologies that rely on high-performance magnets, there is a growing interest in finding new magnetic materials containing cheaper and less critical elements, while maintaining a similar high-performance shown by their RE counterparts. A commercially relevant class of rare-earth free compounds was not identified in Ref. From a combination of data-mining efforts, using ab-initio electronic structure theory, materials synthesis, structural and magnetic characterization, we can report on a new class of rare-earth free permanent magnets, with very promising properties. We have identified Co3Mn2Ge, which is a new material that previously has not been considered as a permanent magnet
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