First-principles study of the easy-plane magnetocrystalline anisotropy in bulk hcp Co1−xIrx

Abstract

The soft magnetic material hcp CoIr has easy-plane magnetocrystalline anisotropy (MA) over a wide range of Ir content and has attracted interest from many researchers. This study presents a comprehensive investigation of the magnetization and MA of bulk hcp Co1−xIrx (0.03≤x≤0.25) alloys based on first-principles calculations. The results reveal that easy-plane MA is obtained for 0.06≤x<0.25, which agrees with the experimental results. The MA arises from the spin-orbit interactions of Co 3d orbitals. The Co1 atoms (the nearest neighbors of Ir atoms) and the Co2 atoms (the second nearest neighbors of Ir atoms) have different local environments; hence, the d orbitals split differently. Numerical calculations prove that the energy level alignment at the two sites plays an important role in determining the orientation of the local spin moments. The Co1 site preferentially adopts an in-plane local spin moment, while the Co2 site exhibits an out-of-plane local spin moment. The competition between the two sites determines the orientation of the easy axis of the hcp CoIr system. Our findings provide guidance for understanding and evaluating experimental studies on manipulating MA in disordered binary alloys.