CHANGE OF THE MAGNETIZATION REVERSAL MECHANISM OF POLYCRYSTALLINE NI-CO THIN-FILMS

Features of the magnetization reversal of thin-film polycrystalline ma gnetic media are revealed by using the magneto-optical indicator film imaging technique. It is shown by a direct visualization that the incr ease in the Co content in Ni100-xCox alloy films leads to a change of the microscopic magnetization reversal mechanism. The magnetization re versal proceeds either by the incoherent spin rotation (at low Co cont ent) or by the nucleation and motion of domain walls (at high Co conce ntration). This behavior results in a nonmonotonic dependence of the c oercivity and remanent magnetization observed in macroscopic magnetiza tion curve measurements. A micromagnetic theory of the magnetization r eversal of polycrystalline magnetic media, which takes into account th e intergranular exchange coupling, is presented. This theory describes qualitatively the change of the magnetization reversal scenario, and explains the surprising magnetic behavior of binary alloys of transiti on metals observed in the experiment. It was also found by using atomi c force microscopy that as-deposited Ni100-xCox films are characterize d by a substantial surface roughness that varies with the change of th e Co content. The relationship between the surface roughness and the c oercivity mechanism in polycrystalline media is also discussed.