CRYSTALLINE FERRIMAGNET-SPINGLASS-AMORPHOUS FERRIMAGNET PHASE TRANSITION IN Tb/Fe MULTILAYERS

The crystallographic structure and the magnetic properties of Tb/Fe sputtered multilayers have been studied as a function of the thickness of Fe-layer (dFe). The crystallographic structure of Fe layer changes from bcc to amorphous at the critical thickness of Fe layer (dFec ≒ 17Å) with decreasing dFe. In corresponding to the change in the crystallographic phase, the magnetic properties of the saturation magnetization Ms, the Kerr rotation angle θk, the Curie temperature Tc and the perpendicular coercivity Hc(⊥) change abruptly at the critical thickness dFec, where the Curie temperature drops to below room temperature and the magnetization curve shows the spinglass like or superparamagnetism like nature at room temperature. Below dFec, with decreasing dFe the Curie temperature Tc increseases owing to the exchange interaction between Fe and Tb around the layer boundaries and then the saturation magnetization increases again approaching the value of the alloys with the same composition. The perpendicular coercivity also increases steeply with decreasing dFe.