Temperature Dependence of Exchange Coupled Multilayers

We present results on an exchange coupled multilayer thin film structure consisting of Py_xCu_1-x (x = 0.4, 0.8, and 1.0) that are exchanged biased (EB) with IrMn, and capped with Ta. The Py_xCu_1-x alloy materials are ordered from bottom to top: Py_0.8Cu_0.2 (20 nm)/ Py_0.4Cu_0.6 (20 nm)/ Py (20 nm). Below T_C of the Py_0.4Cu_0.6 layer, both ferromagnetic layers exhibit EB. As the temperature increases and the system approaches T_C for the Py_0.4Cu_0.6 layer, the portion of the loop corresponding to the bottom, Py_0.8Cu_0.2, layer shifts closer to zero. When T > T_C for the Py_0.4Cu_0.6 layer, the coupling between the top and bottom layers is broken and EB is only observed for the layer in direct contact with IrMn. Vibrating sample magnetometry measurements indicate that the T_C of Py_0.4Cu_0.6 is approximately 100 K, however, we observe EB of the bottom film layer at temperatures greater than T_C. This could be the result of either a proximity effect altering the ordering temperature of the Py_0.4Cu_0.6 or orange peel coupling.