First-Order Reversal Curve (FORC) Features of Ferrimagnetic and Antiferromagnetic Coupled Skyrmions

This work aims to experimentally investigate probing coupled skyrmions in perpendicular magnetic anisotropy multilayers. The first-order reversal curve (FORC) method is a powerful technique to unveil hidden states or subtle behaviors in complex magnetic systems. We focus on two multilayer stacks aiming to antiferromagnetically coupled skyrmions to cancel the skyrmion Hall effect. In the first case, using a ferrimagnetic layer (CoGd/Pt), the skyrmions still present a non-null net magnetization. Helped by magnetic force microscopy, we found that with both high or low Dzyaloshinskii-Moriya interaction, skyrmions tend to merge with magnetic stripes. On the other hand, skyrmions in synthetic antiferromagnetic systems are fully compensated. By varying the spacer thickness in a Co/Pt/Ru multilayer, FORC results exhibit different features depending on the Co/Pt coupling, revealing a complex behavior.