Uniaxial magnetic anisotropy of transition metal oxides: role of local lattice deformation

Abstract

We study the effects of the local lattice structure around magnetic ions, on the uniaxial magnetic anisotropy (MA) in transition metal oxides, particularly ferrites, using the electron theory. We address M-type hexagonal ferrites, tetragonally distorted spinel ferrites, and an ilmenite (CoMnO3). The tight-binding scheme with spin–orbit interaction (LS coupling) is applied to calculate the electronic structure and MA energy of small clusters composed of a transition metal (TM) ion and surrounding oxygen ions. The results of uniaxial MA for M-type ferrites agree with those calculated using the first principles as well as those obtained experimentally, indicating the validity of the present scheme. The high numerical accuracy enables us to conclude that the p − d mixing between Fe3+ and O2− ions is crucial for the uniaxial MA of M-type ferrites and that a change in the local lattice structure around TM ions may cause a sign change in the local uniaxial MA of Fe2+ or Co2+ doped in M-type ferrites. The results of the uniaxial MA in tetragonally distorted spinel ferrites agree well with the experimental ones. These observations may indicate a feasible method to enhance the magnitude of the uniaxial MA in ferrites.