Ion Irradiation Induced Modification of Magnetic Properties in Py-Ta-Multilayers

We have investigated Py-Ta thin film systems with varying numbers of interfaces, but a constant overall thickness of 20 nm Py and 38 nm Ta. The samples have been irradiated with Ne⁺ ions at various fluences in order to modify their magnetic properties, that have been probed using ferromagnetic resonance (FMR), magneto-optical Kerr effect (MOKE), and SQUID magnetometry. The saturation magnetization M_s decreases both with increasing number of Py-Ta inferfaces and with increasing ion fluences. The uniaxial anisotropy of the samples is only of small magnitude and remains almost unaffected. There is a critical fluence depending on the number of interfaces for which ferromagnetism vanishes.