Surface magnetic anisotropy of Co-Hf thin films

In order to investigate the Hf content and the thickness of Co100-xHfx (x = 16, 24, 32 at. %) films we observed the absorption lines of spin wave resonance through the ferromagnetic resonance (FMR) measurement. One volume spin wave mode and two surface spin wave modes were observed for all the samples because of surface anisotropy constants of both sides of the films are less than zero. When the annealing temperature for Co84Hf16 film increased up to 225 oC the surface magnetic anisotropy constant KS2 of the film-substrate interface decreased from -0.07 erg/cm2 to -0.32 erg/cm2 and the KS1 constant of the film-air interface varied from 0.18 erg/cm2 to -47 erg/cm2. In Co76Hf24 film KS2 decreased a little from -0.31 erg/cm2 to -0.41 erg/cm2 and KS1 decreased rapidly from -0.19 erg/cm2 to -0.60 erg/cm2. In general it is shown that the surface anisotropy at the film-air interfaces is very sensitive to Hf content and the annealing temperature. This result is due to the increase of Co content caused by oxidation of Hf atoms near the film-air interface during low temperature annealing (150 to 175 oC) and the diffusion of Co atoms during high temperature annealing (200 to 225oC). (author)