Abstract
We present a study of the effects of strain on the magnetocrystalline anisotropy energy and magnetic moments of Y2Fe14B bulk alloy. The study has been performed within the framework of density functional theory in its fully relativistic form under the generalized gradient approximation. We have studied seven different in-plane a lattice constant values ranging from 8.48 up to 9.08 Å with an increment of δa=0.1 Å. For each a value, we carried out an out-of-plane c parameter optimization, achieving the corresponding optimized lattice pair (a,c). We find a large variation in the site resolved magnetic moments for inequivalent Fe, Y, and B atoms for different lattice expansions and a negative contribution to the total moment from the Y sites. We find a strong variation in the magnetocrystalline anisotropy with the c/a ratio. However, the calculated variation when coupled with thermodynamic spin fluctuations is unable to explain the experimentally observed increase in the total magnetic anisotropy, suggesting that a different physical mechanism is likely to be responsible in contrast with previous interpretations. We show that opposing single- and two-ion anisotropy terms in the Hamiltonian gives good agreement with the experiment and is the probable origin of the non-monotonic temperature dependence of the net anisotropy of Y2Fe14B bulk alloy.
Highlights
Rare-earth (RE) transitional metal permanent magnetic materials play a critical role in hybrid and electric vehicles and electric power generation.[1]
We present a study of the effects of strain on the magnetocrystalline anisotropy energy and magnetic moments of Y2Fe14B bulk alloy
In FePt, the tetragonality of the system contributes to the magnetocrystalline anisotropy (MAE), and we argue that the similar qualitative behavior seen for Y2Fe14B is due to the same physical effect due to the anisotropy of the local electronic environment
Summary
Rare-earth (RE) transitional metal permanent magnetic materials play a critical role in hybrid and electric vehicles and electric power generation.[1]. The most technologically important Nd–Fe–B magnet consists of 2:14:1 phase Nd2Fe14B This Nd–Fe–B magnet has the highest energy product among all known permanent magnet materials.[1] The magnetocrystalline anisotropy (MAE) is a key factor for understanding the high coercivity of RE2TM14M (RE = rare earth, TM = transition metals, and M = B, C, N) permanent magnets.[2] These elements form stoichiometric compounds in the 2:14:1 phase of rare earths, transition metals, and metalloids, respectively, which allows the study of different magnetic couplings RE–RE and RE–TM between the different sites.[3,4,5] Related with the MAE is the effect of strain on these materials since the manufacturing process could promote variations in their lattice parameters and some residual strain.[6–8]
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