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

TL;DR

This study investigates magnetic relaxation in exchange biased (Pt/Co) multilayers with perpendicular anisotropy, revealing how spacer thickness influences reversal mechanisms, with nucleation dominating at maximum exchange bias.

Contribution

It provides detailed analysis of reversal mechanisms in exchange biased multilayers using magneto-optical Kerr effect and Fatuzzo's model, highlighting the role of spacer thickness.

Findings

Reversal dominated by domain wall propagation at 2 nm spacer.

Nucleation dominates at 0.2 nm spacer with maximum exchange bias.

Nucleation density varies between ascending and descending branches.

Abstract

Magnetic relaxation measurements were carried out by magneto-optical Kerr effect on exchange biased (Pt/Co)5/Pt/FeMn multilayers with perpendicular anisotropy. In these films the coercivity and the exchange bias field vary with Pt spacer thickness, and have a maximum for 0.2 nm. Hysteresis loops do not reveal important differences between the reversal for ascending and descending fields. Relaxation measurements were fitted using Fatuzzo's model, which assumes that reversal occurs by domain nucleation and domain wall propagation. For 2 nm thick Pt spacer (no exchange bias) the reversal is dominated by domain wall propagation starting from a few nucleation centers. For 0.2 nm Pt spacer (maximum exchange bias) the reversal is strongly dominated by nucleation, and no differences between the behaviour of the ascending and descending branches can be observed. For 0.4 nm Pt spacer (weaker exchange bias) the nucleation density becomes less important, and the measurements reveal a much stronger density of nucleation centers in the descending branch.