Magnetocrystalline Anisotropy and Magnetostriction in Tetragonally Distorted bcc-Fe and fcc-Ni

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 (E_MCA) with respect to c/a ratio, a degree of tetragonalization. For Ni, E_MCA 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.