Exchange coupling between ferromagnetic fcc Ni81Fe19 and antiferromagnetic bcc CrMnPt films

Abstract

We studied an antiferromagnetic CrMnPtx [(Cr:Mn≂1:1) in atomic percent] film for an exchange-biased layer, focusing especially on the relationships between the exchange coupling properties of the CrMnPtx (top)/Ni81Fe19(bottom) films and the character of its CrMnPtx film. The best Pt content to obtain a large exchange coupling of the CrMnPtx film was 5.0–8.0 at. %. Typically, the exchange coupled 50 nm CrMnPt5−8/40 nm Ni81Fe19 films exhibited a relatively large exchange coupling field of ∼22 Oe and a high blocking temperature of ∼380 °C. Besides, the CrMnPt5−8 film deposited on the Ni81Fe19 film had a considerably high resistivity of ∼300–350 μΩ cm. These large exchange coupling and high resistivity values were obtained only when the α-phase with a disordered bcc structure was stabilized in the CrMnPtx film by the underlying fcc Ni81Fe19 film. The Pt within the CrMnPtx film might localize the Mn magnetic moment. As to why the CrMnPtx film having the Pt content of 5.0–8.0 at. % could give the Ni81Fe19 film a large exchange coupling, this was attributed to the nearest neighbor Mn–Mn atomic distance within the CrMnPt5−8 film being the same as the distance at which the Mn–Mn exchange interaction showed the maximum negative value. Furthermore, the decrease in size of the exchange coupling field and lowered blocking temperature for tCrMnPt<30 nm (tCrMnPt: CrMnPtx film thickness) were thought to originate from a decrease of antiferromagnetic CrMnPtx anisotropy with decreasing tCrMnPt.