Enhancement of exchange-coupling field in FeMn pinned spin valve by surfactant Bi

Ta/NiFe/Cu/NiFe/FeMn/Ta spin valve multilayers with surfactant Bi introduced after deposition of Cu layer were prepared. The enhancement of the exchange bias field has been found in these spin valve multilayers. The composition and chemical states of Bi and Cu at sample surface were examined by X-ray photoelectron spectroscopy. The experiment shows that the Bi as a surfactant with very low surface energy has hindered Cu atoms from segregating to the interface of NiFe/FeMn during the fabrication of the spin valve multilayers. This mechanism would be responsible for the enhancement of the exchange bias field.