Influences of surfactant Bi on the exchange coupling field and microstructure of spin-valve multilayers

Ta(10 nm)/NiFe(8 nm)/Cu(2.6 nm)/NiFe(3.6 nm)/FeMn(9 nm)/Ta(10 nm) spin valve multi-Myers were prepared by magnetron sputtering, It is found that an enhancement of exchange coupling field can he achieved by depositing a Bi layer with appropriate thickness at the Cu/NiFe interface. The results of X-ray photoelectron energy spectra show that the segregation of Cu atoms to the surface of the NiFe layer can he depressed effectively. Excessive Bi atoms can further migrate to the FeMn layer, which may produce lots of impurities. Consequently the ferromagnetism of the FeMn layer is damaged and the exchange coupling field is decreased.