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VIDEO DOI: https://doi.org/10.48448/m9rt-w757

technical paper

MMM 2022

November 07, 2022

Minneapolis, United States

Integrated ab initio computational modelling of magnetic anisotropy and L10 order in non critical transition metal magnets

While CoPt and FePt magnets have high magnetic anisotropy (MAE) when chemically ordered into L10 structures, their components’ high criticality calls for a search for more sustainable systems. Ab initio modelling confirms the pivotal role of the tetragonal order for this useful permanent magnetic property 1. L10-FeNi, found in meteoritic, tetrataenite samples, also has significant uniaxial anisotropy 2,3. We report integrated modelling of ternary FeNi-based alloys of both the propensity for L10 order and the MAE. We study Fe50Ni40X10 alloys (X = Pt, Pd, Al, Ti, Mo, Nb, Ta, W). Crucially, to guide material design, our modelling accounts for the physics that the same electrons which produce the MAE also glue the atoms into their places in the crystal structure. There are 3 steps: 1. The MAE is calculated for an ideal (prescribed) ferromagnetic (FM) L10 ordered material (top figure) - alternating Fe and Ni80X20 layers. These values, per formula unit (FU), are shown in the 5th column (col) of the table. 2. The atomic, short-range order (ASRO) in a high temperature, paramagnetic (PM), f.c.c. solid solution, Fe50Ni40X10 is calculated 4 to learn whether L10 order forms readily (col 2) and to determine the compositions of the alternating layers (col 3) if it does (lower figure). 3. The MAE of the ensuing L10 alloys are calculated (col 4). FM L10 Fe-Ni80Pt20 has a large MAE of 0.39 meV/FU but Fe-Ni80Al20’s value of 0.23meV/FU is significant and twice that of L10-FeNi. The chemical ordering, however, supported by the electrons of the materials, does not lead to these desired atomic arrangements and only the Pt, Pd, Al-doped alloys adopt any L10 order with sharply reduced MAEs (col 4). Comparison of the ASRO in PM and FM Fe50Ni50 solid solutions shows a way to circumvent this issue and explain the L10-order in meteoritic FeNi samples. Spin-polarized electronic structure is paramount to establish L10 order - PM Fe50Ni50 has no propensity whatsoever to adopt this order in sharp contrast to the alloy in a FM state which is predicted to order into the L10 structure below 670K 5.
Research performed in part under the auspices of the U.S. Department of Energy, Office of Science under Award Number DE SC0022168.
1 J. B. Staunton et al., https://doi.org/10.1103/PhysRevB.74.144411
2 R. S. Clarke and E. R. D. Scott, American Mineralogist 65, no. 7-8 (1980): 624-630.
3 N. Maat et al. Acta Materialia. 2020 Sep 1;196:776
4 C. D. Woodgate and J. B. Staunton, https://doi.org/10.1103/PhysRevB.105.115124
5 V. Crisan et al., https://doi.org/10.1103/PhysRevB.66.014416

Figure 1

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Transcript English (automatic)

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