Surface demagnetizing field as a source of uniaxial surface anisotropy in Gd---Co---Mo thin amorphous films

Surface magnetic anisotropy energy was studied for (Gd0.26Co0.74)0.96Mo0.04 and (Gd0.29Co0.71)0.96Mo0.04 thin amorphous films by means of microwave spectroscopy at the X-band within the temperature range 4–295 K. Excitations of surface spin waves were observed in the spin wave resonance spectra. The experiment was performed in a rotating external magnetic field. The angular dependence of the resonance field for the uniform mode (spin wave vector k=0) and the surface mode made it possible to determine the surface uniaxial anisotropy constant Ks and its temperature dependence. An inhomogeneity of the saturation magnetization Ms within a close-to-surface layer of thickness d can generate the surface anisotropy energy with anisotropy constant Ks given by the formula: Ks=4?Mbs (Mbs?Msurfs)d, where the indexes b and surf correspond to the bulk and surface values, respectively. The temperature dependence of Ks calculated by means of the formula agrees qualitatively with temperature dependence of Ks found in the experiment.