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

摘要

We report on the effects of O_2 and H_2 dosing on the magnetism of Co_(75)Fe_(25) 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 O_2 and H_2 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 H_c 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 10 L (1 L = 10~(-6)Torr s)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; 50 L of O_2 caused a rotation of the easy axis by 60 deg 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.