Magnetization reversal via symmetric rotation of layers in exchange biased multilayers

Abstract

We have investigated the magnetization reversal for exchange coupled polycrystalline [IrMn∕CoFe]N multilayers. Polarized neutron reflectivity (PNR) data indicate a simultaneous coherent rotation of all ferromagnetic layers for a sample with N=10 and angles of 45° and 90° between the applied field and the exchange bias direction. On the other hand, magneto-optic Kerr effect (MOKE) measurements, which are sensitive mainly to the two topmost bilayers, reveal a variation of the strength of the exchange bias and the uniaxial anisotropy as a function of N for multilayers with N=1 up to 10. The MOKE data thus indicate the direction of the magnetization to vary from layer to layer for intermediate fields. PNR was found to be insensitive to this variation as the deviation of the layer magnetization directions from its mean value is relatively small (≈10°). These studies demonstrate how the complementary techniques PNR and MOKE can be used to obtain a layer-by-layer vector magnetometry of multilayer stacks.