STUDY OF INTERFACE WALL ENERGY IN EXCHANGE-COUPLED DOUBLE-LAYER FILM

Recently, exchange-coupled multilayer films have been investigated intensively for the magneto-optical recording medium. We studied the interface wall energy density (σw) in the exchange-coupled double-layer TbFeCo films which were prepared by the dc-sputtering method. The composition of the first layer was Tbx(Fe85Co15) 100-x (x=14.0-35.0), and that of the second layer was fixed at the compensation composition of Tb23.8(Fe85Co 15)76.2. The magnitude of σw stored in the boundary was determined by the shift field of the minor hysteresis loop of the first layer measured with VSM. It was found that σw depended on the Tb content of the first layer. As a result, σw was correlated with the perpendicular anisotropy (Ku), and well explained by the formula, σw∝(Ku) 1/2. We can treat the interface wall energy practically as Bloch wall energy; however, σw was determined by the magnetic properties of both layers.