Magnetization and magnetoresistance of Co/GaAs(001) films

We have combined polarised neutron reflection (PNR), X-ray reflection, the extraordinary Hall effect (EHE) and magnetoresistance (MR) in a detailed multi-technique study of the magnetic properties of a 200 Å polycrystalline Co film supported by a GaAs(001) substrate. X-ray reflection and PNR data are found to be well fitted by the same values of layer thickness so providing an additional check on the structural parameters yielded by the fits to the PNR data. Measurements of the reflected neutron polarisation for the same 200 Å Co film are consistent with a layer averaged moment of 1.6μ B and a magnetisation profile in which the moment per Co atom reaches 1.7μ B in the interior of the film and falls to 0.8μ B in a 20 Å thick layer at the GaAs interface. A perpendicular saturation field of 1.39 T is obtained from EHE measurements extended to 20 T on the same sample, from which we estimate a small perpendicular anisotropy field which opposes the demagnetising field. This result indicates that the magnetisation profile is not associated with a large interface anisotropy energy.