TEMPERATURE-DEPENDENCE OF SURFACE AND VOLUME ANISOTROPY IN GD/W(110)

The magnetic anisotropy of epitaxial Gd(0001) films on W(110) is determined as a function of temperature (150 to 350 K) and film thickness (9 to 30 monolayers) by in situ ferromagnetic resonance. The total anisotropy is separated into a thickness-independent part K-V(T) and a thickness-dependent contribution K-S(T)/d. The order of magnitude of K-V (K-V(t = 0.85) = 0.014 meV/atom) and its temperature dependence are comparable to bulk Gd with a change in sign near 0.7 T-c. K-S on the other hand decreases linearly from 1.2 meV/atom at 0.6 T-c to zero at T-c. The 1/d thickness dependence is mainly attributed to a Neel-type surface anisotropy with only small magnetostrictive contributions. As a result we extrapolate a reorientation of the easy axis of the magnetization from in-plane into out-of-plane at low temperatures and thicknesses. From the broadened ferromagnetic resonance line we deduce that a 30 ML film after annealing to 830 K consists of large islands with lateral dimensions of about 180 nm. For the given range of thickness no change of the magnetic moment per Gd atom was observed.