Abstract
The interlayer exchange coupling between two permalloy layers with Ru spacer layer was studied by longitudinal magneto-optical Kerr effect, X-ray diffraction and X-ray magnetic circular dichroism. Oscillations of MR and exchange coupling vs Ru spacer thickness have been observed. The first maximum of the coupling strength appears at 0.7 nm of Ru with oscillatory period of 1 nm. However, a large GMR effect does not observed at this Ru thickness. The missing GMR effect of this system might be due to the strong biquadratic coupling of permalloy layers. It is suggested this biqudratic coupling might be due to the rough interface morphology between permalloy layer through the Ru space layer. With the MCD experiment result, a 400% enhancement of orbital moment of Fe in the permalloy /Ru/ permalloy trilayer system was found at the thickness of Ru spacer layers of antiferromagnetic coupling between permalloy layers. The MCD asymmetry ratios deduced from the Fe, Ni L2,3-edge show a similar oscillation correlated to the interlayer exchange coupling. Grazing incidence X-ray diffraction was used to study the structure of the epitaxial films. Both the permalloy and Ru layers have no significant strains appeared to correlate with this orbital moment enhancement. Strain might not be the major issue to cause the enhancement of orbital moment. Besides, this large enhancement was not found for Py/Ru bilayer system which implies this effect might not depend only on the hybridization of the Fe-3d and Ru-4d electrons at one interface only. It is suggested this effect might be due to the interference between two interfaces.