Distinct evolution of magnetism and anisotropy of ultrathin CoFe and Co films on Cu(110) upon gas adsorption

Abstract

We report on the effects of O2 and H2 dosing on the magnetism of Co75Fe25 films, highlighting the extreme sensitivity of the magnetic behavior of ultrathin films to specific chemical interactions at the surface. We have performed a systematic in situ study of the magnetic behavior as a function of O2 and H2 dosage on ultrathin CoFe and Co films grown on Cu(110) by means of the magneto-optical Kerr effect and low energy electron diffraction. Oxygen and hydrogen dosing are found to have distinctly different influences on the evolution of the coercive field Hc of the CoFe and Co films. Significant differences become also apparent for the evolution of the M-H loop squareness upon gas adsorption. Oxygen dosing leads to a rapid decrease in squareness above 10L (1L≡10−6Torrs) for CoFe films. For Co films, however, the squareness increases initially and then stabilizes at a higher dosage level. Furthermore, a striking sensitivity of the easy axis magnetization in the CoFe films was observed; 50L of O2 caused a rotation of the easy axis by 60° within the plane. The observed differences between the different gases and between the different ferromagnetic films are briefly discussed in terms of d band occupation and details of chemical bonding.

Spin-engineering in the Co75Fe25/Cu(110) system

“…Firstly, for gas doses up to E10 L (1 L 10 À 6 Torr) the coercive field is seen to oscillate; this is believed to be due to ordered dissociative adsorption; in the second region, for exposure to over 10 L of H 2 and O 2 , H C is seen to stabilise or steadily increase, respectively, due to the formation of a surface oxide. Furthermore, exposure of a 7 ML Co 75 Fe 25 film to 50 L of O 2 caused an in-plane rotation of the easy axis of magnetisation of around 601, and a change in the total anisotropy from a mixture of cubic and uniaxial to a purely uniaxial anisotropy [40]. Fig.…”