Dependence of the coercive field on the Cu overlayer thickness in thin Co/Cu(001) and Ni/Cu(001) fcc epitaxial films

We have studied the effect of the Cu overlayer thickness t(Cu) on the coercive field H-c of epitaxial ultrathin fcc Co/Cu(001) and Ni/Cu(001) films by magneto-optic Kerr effect magnetometry. The Cu/40 Angstrom Ni/Cu(001) system shows perpendicular magnetic anisotropy (PMA) for the whole t(Cu) range studied (20-180 Angstrom) with H-c showing a large, linear increase with t(Cu) (from similar to 280 to similar to 360 Oe). On the other hand, the Cu/36 Angstrom Co/Cu(001) structure has dominant in-plane anisotropy and in contradistinction with the Ni case the coercive field decreases rapidly with t(Cu) (from 140 Oe for t(Cu) = 20 Angstrom to similar to 90 Oe at t(Cu) similar to 180 Angstrom). The variation in coercivity is described in terms of the magnetoelastic energy contribution to the magnetic anisotropy induced by the Cu overlayers (via strain). In particular, the increase in the H-c of Ni is attributed to an increase in the PMA while the relation between the magnetic anisotropy and coercivity in the case of Co remains unclear. (C) 2001 American Institute of Physics.