Magnetocrystalline anisotropy (MCA) is a preference of direction of magnetization, a fundamental characteristic of magnetic materials. In cubic crystals like bcc-Fe and fcc-Ni, MCA vanishes identically due to symmetry. However, the tetragonal distortion along the z-axis can induce a non-vanishing MCA by breaking the cubic symmetry. Using first-principles calculations, we analyze magnetocrystalline anisotropy energy (EMCA) with respect to c/a ratio, a degree of tetragonalization. For Ni, EMCA is found to be -78 µeV/atom and +89 µeV/atom, while for Fe, it is +44 µeV/atom and -41 µeV/atom at c/a = 1.05 and 0.95, respectively. Based on the analysis of electronic structure, we reveal how band shifts associated with tetragonal distortion drive the MCA. Furthermore, magnetostriction coefficients (λ001) are evaluated, producing values of 23 ppm for Fe and -52 ppm for Ni, consistent with experimental observations.
Yoo et al. (Tue,) studied this question.