Effects of spacer layers on magnetic properties and exchange couplings of Nd–Fe–B/Nd–Ce–Fe–B multilayer films**Project supported by the Major State Basic Research Development Program of China (Grant No. 2014CB643701) and the General Program of the National Natural Science Foundation of China (Grant No. 51571064).

Abstract

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 4πMr and Hcj 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) = −ΔMirr/2Mr 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.