Accessing different spin-disordered states using first-order reversal curves

Abstract

Combined first-order reversal curve (FORC) analyses of the magnetization ($\mathrm{M}$-FORC) and magnetoresistance (MR-FORC) have been employed to provide a comprehensive study of the $\mathrm{M}$-MR correlation in two canonical systems: a NiFe/Cu/FePt pseudo spin valve (PSV) and a ${[\mathrm{Co}/\mathrm{Cu}]}_{8}$ multilayer. In the PSV, due to the large difference in switching fields and minimal interactions between the NiFe and the FePt layers, the $\mathrm{M}$ and MR show a simple one-to-one relationship during reversal. In the ${[\mathrm{Co}/\mathrm{Cu}]}_{8}$ multilayer, the correlation between the magnetization reversal and the MR evolution is more complex. This is primarily due to the similar switching fields of, and interactions between, the constituent Co layers. The FORC protocol accesses states with much higher spin disorders and larger MRs than those found along the conventional major loop field cycle. Unlike the $\mathrm{M}$-FORC measurements, which only probe changes in the macroscopic magnetization, the MR-FORCs are more sensitive to the microscopic domain configurations as those are most important in determining the resultant MR effect size. This approach is generally applicable to spintronic systems to realize the maximum spin disorder and the largest MR.