On the origin of magnetic anisotropy in 4f-free ferromagnets based on the CaCu₅ structure

Using first-principles calculations, we investigate the origin of magnetocrystalline anisotropy in a series of 4f-electron-free intermetallics with CaCu₅-based structures: YCo₅, YCo₄B, and Y₃Co₁₃B₂. The electronic structure of these compounds is characterized by a set of narrow 3d bands near the Fermi level. In YCo₅ the easy-axis anisotropy originates primarily in the spin-orbit coupling-induced mixing of the electronic states with Co d x 2 − y 2 and d x y character. The analysis of k-resolved anisotropy shows that positive contributions accumulate from the entire Brillouin zone but are particularly large near the k z = 0 plane. The analysis of the single-site and two-site terms reveals a large positive single-site contribution to the magnetocrystalline anisotropy from the Co atoms on the honeycomb sublattice, along with two-site contributions from both honeycomb and kagome sublattices.