Mesoscale magnetic rings: Complex magnetization reversal uncovered by FORC

In this work, we investigate mesoscopic amorphous magnetic rings prepared by ion-implantation. The analysis is carried out combining conventional magnetization vs field measurements alongside MOKE microscopy imaging and, for the first time, first-order reversal curves (FORCs). With the information extracted from the FORC diagram, we can identify the presence of typical onion and vortex magnetic configurations, and also determine with high resolution the fields connected to their formation, stability, and annihilation. Furthermore, depending on the field and history, two different onion configurations exist, characterized by the presence of transverse or vortex domain walls. The FORC data reveal the different reversible/irreversible nature of the annihilation of the two onion configurations, and a signal peculiar of the presence of vortex domain walls. All these crucial information are not accessible with conventional M(H) loops, demonstrating that FORCs offer a unique perspective for the investigation of the physical phenomena of magnetic elements with complex geometries.