Effect of the Cu capping thickness on the magnetic properties of thin Ni/Cu(001) films

We have studied the effect of the Cu capping thickness (in the range 20 les s than or equal to t(Cu) less than or equal to 180 Angstrom) on the magneti c and structural properties of ultrathin FCC 40 Angstrom Ni/Cu(0 0 1) films by means of magneto-optic Kerr effect (MOKE) magnetometry, polarised neutr on reflection (PNR) and grazing incidence X-ray surface diffraction (GID) m easurements. MOKE measurements show that perpendicular magnetic anisotropy (PMA) is observed for the whole of the Cu thickness range studied, while an increased of the coercive field with t(Cu) is found. The variation of the in-plane strain in the Ni film is shown to increase monotonously between 20 and 90 Angstrom Cu capping thickness from - 1.60 +/- 0.03% to - 1 86 +/- 0 .07% as revealed by GID, while PNR measurements show a marked decrease in t he Ni magnetic moment per atom with increasing Cu capping layer thickness, from 0.54 +/- 0.03 mu (B) for t(Cu) = 50 Angstrom to 0.45 +/- 0.03 mu (B) f or t(Cu) = 180 Angstrom. These results clearly show that a strain-induced r eduction in the Ni magnetic moment per atom occurs. The increase in the coe rcive field is also attributed to the increase in the strain of the Ni film . (C) 2001 Published by Elsevier Science B.V.