Magnetic relaxation measurements of exchange biased (Pt/Co) multilayers with perpendicular anisotropy

摘要

Magnetic relaxation measurements were carried out by magneto-optical Kerreffect on exchange biased (Pt/Co)5/Pt/FeMn multilayers with perpendicularanisotropy. In these films the coercivity and the exchange bias field vary withPt spacer thickness, and have a maximum for 0.2 nm. Hysteresis loops do notreveal important differences between the reversal for ascending and descendingfields. Relaxation measurements were fitted using Fatuzzo's model, whichassumes that reversal occurs by domain nucleation and domain wall propagation.For 2 nm thick Pt spacer (no exchange bias) the reversal is dominated by domainwall propagation starting from a few nucleation centers. For 0.2 nm Pt spacer(maximum exchange bias) the reversal is strongly dominated by nucleation, andno differences between the behaviour of the ascending and descending branchescan be observed. For 0.4 nm Pt spacer (weaker exchange bias) the nucleationdensity becomes less important, and the measurements reveal a much strongerdensity of nucleation centers in the descending branch.