Defect-induced modulation of the exchange anisotropy by swift heavy ion irradiation in Ni81Fe19/Ir7Mn93 bilayers

This study investigates the influence of swift heavy ion irradiation on exchange anisotropy (H-EA) and coercivity (H-C) in a set of top-pinned SiOx/Cu/Ni81Fe19/Ir7Mn93/Ta bilayers fabricated by ion beam sputtering at room temperature (RT) in presence of an in-plane in situ static field of 1 kOe. Subsequently, the bilayers were subjected to a magnetic annealing process at 300 degrees C for an hour in the presence of a 3.5 kOe magnetic field. By systematically increasing the Au ion fluences from pristine to 3.3 x 10(11) ion/cm(2), the positive exchange anisotropy (PEA) and negative exchange anisotropy (NEA) were found to be enhanced by 10 Oe and similar to 178 Oe, respectively. However, once the ion fluences surpassed the necessary threshold of 3.3 x 10(11) ion/cm(2) required for defect creation/pinning centers in the antiferromagnetic (AF) layer, a reduction in both H-EA and H-C was observed due to the interfacial mixing. The enhancement in PEA and NEA is attributed to the creation of defects or hyperthermal heating in the AF layer as a consequence of ion irradiation. These experimental results align with the framework of the diluted antiferromagnetic model. The persistent training effect, which is observed even after irradiation, confirms the existence of a highly metastable interface between the NiFe/IrMn layer. Thus, ion irradiation emerges as a powerful tool for precisely tailoring the H-EA and H-C of the bilayers by systematically controlling the ion fluence.