Magnetic properties of epitaxial NiFe/Cu/Co spin-valve structures on GaAs(001)

Cu(50 Angstrom)/NiFe(60 Angstrom)/Cu(60 Angstrom)/Co(20 Angstrom) epitaxial spin-valve structures were grown on GaAs(001) substrates by molecular-beam epitaxy at room temperature. In situ reflection high-energy electron diffraction measurements indicate the stabilization of the bcc-Co(001) phase on 1x1 unreconstructed GaAs(001) for thicknesses up to 20 Angstrom and the epitaxial growth of the fcc-Cu(001) spacer layer and fcc-FeNi(001) top magnetic layer. Magneto-optical Kerr effect and Brillouin light-scattering measurements of the composite structure showed that a fourfold cubic anisotropy is present but a twofold anisotropy also occurs directed along the < 110 > axes. The easy cubic axes are directed along the < 100 > axes, which implies that the cubic anisotropy constant K-l for bcc-Co is positive. The magnetic anisotropy of the bcc-Co layer has a striking influence on the magnetoresistance characteristics which were found to be angular dependent. A simulation of this mixed anisotropy behavior yields quantitative agreement with the experimental results. (C) 2000 American Institute of Physics. [S0021-8979(00)47808-4].