Initialization of unidirectional anisotropy in a ferromagnet-antiferromagnet bilayer by keV-He ion bombardment

A polycrystalline Cu/Ni80Fe20/Mn83Ir17/Co/AlOx ferromagnet-antiferromagnet layer system grown without applying an external magnetic field shows no unidirectional anisotropy in the as-prepared state. After 10 keV-He ion bombardment in an external in-plane magnetic field, a clear unidirectional anisotropy collinear to the magnetic field direction during bombardment is observed, indicating that ion bombardment can be used for this system to initialize the unidirectional exchange anisotropy. The magnetization reversal processes for various ion doses are discussed, based on longitudinal magnetooptical Kerr-effect measurements.