Asymmetry of nucleation density and its variation with Pt spacer thickness in exchange-biased [Pt/Co]5/Pt/FeMn multilayers

The magnetization reversal of perpendicular exchange-biased [Pt/Co]5/Pt/FeMn multilayers was investigated by magneto-optical Kerr microscopy. The effect of varying the Pt interlayer thickness between the topmost Co layer and the FeMn layer was studied. Our measurements reveal that coercivity (HC) and exchange bias field (HEB) vary with Pt spacer thickness, and have a maximum for a Pt thickness of 0.4 nm. Magnetization reversal measurements show that, for the unbiased multilayer, the reversal is dominated by domain wall propagation starting from a few nucleation centers. For the exchange-biased multilayers, magnetization reversal occurs by nucleation and domain wall propagation with a variation in the nucleation density. For 0 and 0.2 nm Pt spacer, no difference is observed in the nucleation density of the ascending and descending branches unlike for 0.4 and 0.6 nm Pt spacer where the measurements reveal a larger density of nucleation centers in the descending branch.