The metastable Fe and Tb phases in Fe/Tb thin films and their magnetic properties

Abstract Experimental investigations of microstructure and magnetic properties of vapor-deposited Fe/Tb multilayers are presented in this paper. It is found that Fe transforms from the BCC polycrystalline structure into an amorphous one with the decrease of Fe layer thickness and that Tb has a metastable FCC crystalline structure in the thin films. Film magnetization behavior and the perpendicular magnetization anisotropy (PMA) tendency are investigated by means of a vibrating-sample magnetometer. The results show that the magnetic properties strongly depend on the layer thickness of the constituent metals, i.e., the films change from ferromagnetic into superparamagnetic when t Fe ⩽1.4 nm. Volume anisotropy is estimated to be 2.6×10 6 erg/cm 3 for t Tb =2.1 nm Fe/Tb multilayers and 2.2×10 6 erg/cm 3 for t Tb =10.7 nm Fe/Tb multilayers. The amorphous Fe in Fe/Tb multilayers is important to induce PMA that can be interpreted in terms of anisotropic distribution of Tb–Fe pairs aligned perpendicular to the film plane.