Unveiling the mechanisms governing the exchange coupling and coercivity modifications in annealed or ion-irradiated Ir-Mn/Fe/Co and Ir-Mn/Ni-Fe/Co films

Abstract

We investigate the modifications of the exchange bias, effective ferromagnet-antiferromagnet (FMAFM) coupling, and coercivity in annealed or ion-irradiated Ir-Mn/spacer layer (SL)/Co trilayers. A ferromagnetic, either Fe or permalloy (Py), thin SL or a nonmagnetic Ru one with different thicknesses (tSL) is used. The magnetic characterization is performed at room temperature via conventional magnetometry and, partly, via soft-x-ray magnetic circular dichroism. The latter shows that at the FM-AFM interface there is small uncompensated Mn magnetization coupled, preferentially, antiferromagnetically to Fe moments. This indicates the formation of small FeMn clusters that reverse their magnetizations together with those of Co, Ni, and the rest of Fe. Neither annealing nor ion irradiation of the films with tFe ≥ 0.5 nm changes significantly the pinning part of the FM-AFM interface. In the Py-spacer films, however, the great tendency of Mn to interdiffuse with Ni leads to a decrease of the Ir-Mn anisotropy at the interface, lowering its pinning capacity. While defects created in the bulk of the AFM are mainly responsible for the changes of the magnetic characteristics of the Ir-Mn/Fe/Co films, interdiffusion and defect creation at the FM-AFM interface are the respective mechanisms determining the behavior of the Py-spacer series. These conclusions are reinforced by results for the Ru-spacer series.