Interlayer Segregation of Cu Atoms in Metal Multilayers

The experimental results show that the exchange coupling field H_ex of NiFe/FeMn for Ta/NiFe/FeMn/Ta multilayers is higher than that for the spin valve multilayers Ta/NiFe/Cu/NiFe/FeMn/Ta. The composition and chemical states at the surface of Ta(12 nm)/NiFe(7 nm), Ta(12 nm)/NiFe(7 nm)/Cu(4 nm) and Ta(12 nm)/NiFe(7 nm)/ Cu(3 nm)/NiFe(5 nm) were studied by using the x-ray photoelectron spectroscopy. The results show that no element from the underlayers floats out or segregate to the surface for Ta(12 nm)/NiFe(7 nm), Ta(12 nm)/NiFe(7 nm)/ Cu(4 nm). However, Cu atoms segregate to the surface of Ta(12 nm)/NiFe(7 nm)/Cu(3 nm)/NiFe(5 nm) multilayers, i.e. to the NiFe/FeMn interface for Ta/NiFe/Cu/NiFe/FeMn/Ta multilayers. The authors believe that the presence of Cu atoms at the interface of NiFe/FeMn is one of the important factors which will cause the exchange coupling field H_ex of Ta/NiFe/FeMn/Ta multilayers to be higher than that of Ta/NiFe/Cu/NiFe/FeMn/Ta multilayers.