MAGNETIC-PROPERTIES OF ULTRATHIN CO/AG(001) FILMS

We have used polarised neutron reflection to investigate the saturated in-plane magnetisation of ultrathin single Co films incorporated into Ag/Co/Ag(001) epitaxial sandwich structures. For Co thicknesses of 1 and 2 monolayers (ML) we find ferromagnetic order at 5 K with moments per Co atom close to 2.0-mu(B), significantly exceeding the bulk hcp phase value of 1.7-mu(B). For a Co thickness of 3ML we find a ferromagnetic moment close to 1.7-mu(B) at 5 K with the moment falling significantly beneath this value for a 5ML film. The collapse of the effective magnetic moment is attributed to the strain-induced structural disorder of the film observed during growth beyond 3ML. Surface magneto-optic Kerr effect measurements reveal large in-plane magnetic anisotropies and high Curie temperatures for Co thicknesses in the 1-3ML range. A weak temperature-dependence of the magnetisation M(T) is observed for a 2ML film.