NMR studies of magnetic multilayers

In connection with giant magnetoresistance and long-range exchange coupling between magnetic layers, both the spatial distribution of the local magnetic field in nonmagnetic layers and the interface magnetism in magnetic layers have been investigated using the NMR technique in [Ni/Cu/Ni], [Co/Cu/Co] and [Fe/V/Fe] multilayers. From the analysis of the Cu and V NMR spectra (distribution of the local magnetic field), two characteristic features have emerged: (a) the conduction electron polarization in the nonmagnetic spacer layers due to the magnetic layers has a long-range nature and manifests itself in an oscillatory distribution of the Cu NMR shift, and (b) the distribution of the shift, and hence the distribution of the magnetic-moment-induced spin polarization in the nonmagnetic layers, depends strongly on the orientation of the external magnetic field to the layer plane. The interface magnetism, which is strongly related to the interface atomic arrangements, has also been studied from the analysis of the distribution of the hyperfine field of ferromagnetic atoms observed by zero-field ferromagnetic nuclear resonance (FNR). In Cu/Co superlattices, there has been observed a correlation between the magnetoresistance ratio and the interface structure determined by the hyperfine field distribution.