Magnetocrystalline anisotropy of epitaxially grown FeRh/MgO(001) films

We quantitatively investigated the magnetocrystalline anisotropy (MCA) of metamagnetic FeRh films epitaxially grown on MgO(001) substrates. The in-plane fourfold magnetic anisotropy of epitaxial FeRh films is reoriented from the<100>to<110>directions and meanwhile the strength is obvious enhanced when FeRh transfers from the ferromagnetic (FM) to antiferromagnetic (AF) states. In the nominal AF state, the observed fourfold magnetic anisotropy originates from the exchange coupling between the residual FM moments caused by antisite defects and the AF matrix, which therefore indicates the orientation and strength of the MCA of AF FeRh. The steep increase of the FM resonance linewidth when crossing the FM-AF phase transition temperature reveals the enhanced effective magnetic damping and an increased fourfold anisotropic two-magnon scattering. The first-principles calculations suggest that the in-plane lattice compressive strain imposed by the MgO substrate plays an important role in determining the magnetic structures FeRh films.