Double-Loop Hysteresis Behavior and Competing Exchange Interactions in IrMn/NiFe Bilayers.

In this work, we investigate the magnetization switching behavior of IrMn/NiFe bilayers as a function of NiFe thickness, temperature, and cooling-field direction. An unusual double-loop hysteresis behavior is observed in IrMn 10 nm/NiFe 40 nm bilayers, whereas a conventional single-loop hysteresis behavior is obtained for thinner NiFe layers. The observed double-loop feature exhibits temperature- and cooling-field-dependent asymmetry, suggesting a spatially nonuniform exchange interaction at the IrMn/NiFe interface. The opposite evolution of switching fields under positive and negative cooling fields indicates competing exchange contributions within the bilayer system. These results are consistent with a model involving distinct interfacial exchange regions or nonuniform uncompensated spin configurations in the IrMn layer. Our findings provide insight into the complex interfacial exchange behavior responsible for double-loop hysteresis in IrMn/NiFe bilayers and highlight the importance of interfacial magnetic inhomogeneity in exchange-biased spintronic structures.