Interplay between magnetic moment and magnetocrystalline anisotropy in tetragonally distorted galfenol films

Magnetic properties of Fe100−xGax (x = 15 and 30) epitaxial thin films on GaAs(001) substrates were studied experimentally and theoretically. The samples grown by molecular beam epitaxy under certain conditions adopt body-centered structures with tetragonal distortion along the film normal with a c/a ratio varying from 1.014 to 1.036. The density functional theory (DFT) calculations were performed for different (c/a) ratio values and Ga contents. DFT results showed that Fe atoms placed at the first neighborhood of Ga positions present a much stronger distortion in the local exchange-correlation field than second neighbor Fe atoms. The formation of non-bonding Fe 3d states in the minority spin sub-band and the predominance of hybridization of Ga 4p states with Fe 4p states due to Ga content cause this magnetic behavior. The in-plane magnetic anisotropies are explained in terms of the exchange-correlation field isosurfaces. As a result of that, the global magnetic anisotropy can be described as cubic magnetocrystalline mixed with sixfold anisotropy.