Critical curves in NiFe/FeMn bilayers with varying antiferromagnetic layer thickness

The effect of antiferromagnetic (AF) layer thickness on exchange bias was studied in a series of NiFe(50 nm)/FeMn(t) bilayers through both irreversible and reversible experiments at room temperature. The exchange bias was evaluated in the sample plane both through measurement of the major hysteresis loops and probing the reversible susceptibility. The critical curve was constructed to map the angular dependence of the magnetization switching and exchange bias, which is found to evolve as a function of AF layer thickness. Ferromagnetic resonance absorption was measured at several frequencies and angles, and angular-dependent absorption curves were plotted. A comparison is made between the recorded exchange bias using the three methods. The measurements reported are supported by simulations under a generalized Stoner-Wohlfarth model, and general limitations of the experiment are discussed.