STRUCTURE AND MAGNETIC-PROPERTIES OF SPUTTERED TB/CO MULTILAYERS

Multilayers of Tb/Co with equal thicknesses of the single layers (d(Tb) = d(Co)) were prepared on water-cooled quartz and glass substrates by means of a two-source rf-sputtering method. Small-angle X-ray diffraction analysis and transmission electron microscopy on cross-sections of the films revealed a layered structure in all samples with d(Tb), d(Co) greater-than-or-equal-to 15 angstrom. The films with d(Tb), d(Co) less-than-or-equal-to 10 angstrom behaved as homogeneous TbCo alloys. The existence of compensation points in the temperature dependence of the magnetization of the multilayers indicates a magnetic order in the Tb layers with an antiferromagnetic coupling between the Th and Co atoms in spite of the fact that pure Th is paramagnetic at room temperature (T(C) = 219.5 K). The extension of the magnetically coupled regions in the Th layers was calculated from the dependence of the saturation magnetization M(S) and the compensation temperature T(comp) on the layer thickness d(L) of the Tb/Co multilayers. It is about 15 angstrom at each boundary of the Tb layers and therefore much larger than one would expect from the direct exchange interaction in the ferromagnetic transition metals. The magnetic anisotropy constant K(u)eff of the films was determined by a torque magnetometer. The linear dependence of K(u)eff on the inverse layer thickness 1/d(L) of the multilayers indicates the existence of a surface anisotropy at the Tb/Co interfaces. The surface anisotropy constant is about K(s) = 0.46 erg/cm3.