Exchange bias and compositional depth profiles of annealed NiFe/FeMn/CoFe trilayers

摘要

We investigate the exchange bias fields and compositional depth profiles of the NiFe (bottom)/FeMn/CoFe (top) trilayers after a thermal treatment at different annealing temperatures. Interestingly, the magnetic hysteresis measurement revealed that the NiFe/FeMn/CoFe trilayers exhibit a contrasting variation of the exchange bias fields at the two interfaces in a completely different way to each other. High angle x-ray diffraction indicates that there is no distinguishable effect of a thermal treatment on the NiFe (111) and FeMn (111) peaks. The Ni 2p and Mn 2p x-ray photoelectron spectroscopy (XPS) spectrums near these two interfaces along with the XPS compositional depth profiles are measured. We find the asymmetric depth profiles of the Fe and Mn atoms throughout the FeMn layer and the preferential Mn diffusion into the NiFe layer compared to the CoFe layer. We believe that in situ applied fields during sample growth and ex situ cooling fields after sample growth have a different effect on the exchange bias fields of both top and bottom interfaces.