Influence of strain and substitution on magnetocrystalline anisotropy of R2 Fe14 B (R = Pr , Dy and Y)

The intermetallic rare earth-transition metal (R - T) compound Nd₂Fe₁₄ B has a large energy density and is an industrially important permanent magnet material. Its low Curie Temperature (T_C) though limits its use for electric motor applications. To improve its high temperature permanent magnetic properties, the coercive field (H_C) should be enhanced, which can be achieved by influencing intrinsic atomistic properties such as saturation magnetization (M_S) and magnetocrystalline anisotropy energy (MAE). Strain effects and substitution are two important methods for influencing M_S and MAE. Using numerical methods based on density functional theory, firstly M_S and MAE of three R₂Fe₁₄ B compounds with R = Pr , Dy and Y are calculated at 0 K. Further, the influence of changing the lattice parameter ratio c / a on MAE is studied. For increasing c / a , MAE of Y₂ Fe₁₄ B and Pr₂ Fe₁₄ B remains nearly constant, while MAE of Dy₂ Fe₁₄ B decreases monotonously, up to 40 % per 1 % change in c / a . In the next step, 50 % of the R - atoms are substituted. For Pr₂ Fe₁₄ B , MAE decreases with substitution of Dy and Y; for Dy₂ Fe₁₄ B it increases with Pr but decreases with Y; for Y₂ Fe₁₄ B it increases with Pr and Dy . The nucleation field (H_N) of the substituted phases are estimated for different microstructures and visually compared to the non-substituted compounds, showing a large H_N for (PrDy) Fe₁₄ B . Further, based on DOS plots of the (Y - Dy) Fe₁₄ B system, the contribution of different atoms and atomic sites to MAE is discussed, and by visualizing the electronic density contours, the influence of substitution on Fe - atoms in Dy₂ Fe₁₄ B and (DyY) Fe₁₄ B is studied.