Effect of L12 ordering in antiferromagnetic Ir-Mn epitaxial layer on exchange bias of FePd films.

Two series of samples of single-layer IrMn and IrMn/FePd bilayer films, deposited on a single-crystal MgO substrate at different IrMn deposition temperatures (T_s=300-700 °C), were investigated using magnetron sputtering. L12 ordering was revealed for the 30nm-thick IrMn epitaxial (001) films with T_s⩾400 °C, determined by synchrotron radiation x-ray diffractometry (XRD). XRD results also provide evidence of the epitaxial growth of the IrMn films on MgO substrate. Increasing T_s from 400 to 700 °C monotonically increases the ordering parameter of L12 phases from 0.17 to 0.81. An in-plane exchange bias field (H_eb) of 22Oe is obtained in a 10nm-thick FePd film that is deposited on the disordered IrMn films. As the L1₂ ordering of the IrMn layers increases, the H_eb gradually decreases to 0Oe, meaning that the exchange bias behavior vanishes. The increased surface roughness, revealed by atomic force microscopy, of the epitaxial IrMn layers with increasing T_s cannot be the main cause of the decrease in H_eb due to the compensated surface spins regardless of the disordered and ordered (001) IrMn layers. The change of antiferromagnetic structure from the A1 to the L1H₂ phase was correlated with the evolution of H_eb. [ABSTRACT FROM AUTHOR]