NMR AND MAGNETIZATION STUDIES OF CO/CU SUPERLATTICES

Co NMR and magnetization have been measured in a series of Co/Cu superlattices grown by molecular-beam epitaxy, with Co thicknesses varying from 5 to 100 angstrom. The Co structure is mainly fcc for thicknesses of up to 65 angstrom. For thicker Co layers the structure becomes hcp. For thin layers it is shown that the hyperfine field corresponding to fcc regions is nearly isotropic, whereas that arising from faulted (hcp) regions is anisotropic, with the symmetry axis parallel to the film normal. The anisotropic part of this field has the same sign and order of magnitude as in bulk hcp Co. For the sample with 5-angstrom Co layers the dispersion of the magnetocrystalline anisotropy over the sample can be ascribed to Co-layer thicknesses which vary from 2 to 3 monolayers (4 to 6 angstrom) throughout the sample.