Effects of spacer layers on magnetic properties and exchange couplings of Nd-Fe-B/Nd-Ce-Fe-B multilayer films

The influences of the spacer-layer Ta on the structures and magnetic properties of NdFeB/NdCeFeB multilayer films are investigated via DC sputtering under an Ar pressure of 1.2 Pa. An obvious (00l) texture of the hard phase is observed in each of the films, which indicates that the main phase of the film does not significantly change with Ta spacer-layer thickness. As a result, both the remanence and the saturation magnetization of the magnet first increase and then decrease, and the maximum values of 4π M_r and H_cj are 10.4 kGs (1 Gs=10^-4 T) and 15.0 kOe (1 Oe=79.5775 A·m^-1) for the film with a 2-nm-thick Ta spacer-layer, respectively, where the crystalline structures are columnar shape particles. The measured relationship between irreversible portion D (H)=-△ M_irr/2M_r and H indicates that the nucleation field of the film decreases with spacer layer thickness increasing, owing to slightly disordered grains near the interface between different magnetic layers.