Annealing effect of surface magnetic properties in amorphous Co1-xTix thin films

For amorphous Co_1-xTi_x (x=0.13, 0.16, 0.21 at.%) thin films, deposited by the DC magnetron sputtering method, ferromagnetic resonance experiments have been used to investigate the dependence of surface magnetic properties in relation to annealing temperatures (150~225°C). Spin wave resonance spectra for all annealing temperatures consist of several volume modes and one (or two) surface mode. It is suggested that both surfaces of the film have a perpendicular hard axis to the film plane (negative surface anisotropy). Also, the surface anisotropy K_s2 at the substrate-film interface is varied slowly from -0.11 to -0.25 erg/cm² and the surface anisotropy K_s1 at the film-air interface is varied from 0.16 to -0.53 erg/cm² with increasing annealing temperatures. We conjecture that the variation of surface anisotropy K _s1 is due to the increase of Co concentration resulting from Ti oxidation for low temperature annealing (150-200°C) and the diffusion of Co atoms near the film surfaces for high temperature annealing (225-250°C)