Large exchange bias and high stability of CoFe/CrPt films with L1_0 CrPt as the pinning layer

摘要

We have studied an antiferromagnetic L1_0 CrPt film as a pinning layer. dc magnetron sputtered [Pt/Cr] multilayers on a Co_(0.9)Fe_(0.1) layer exhibit no exchange bias. After being annealed at 350℃ for 5 h in a vacuum, the equiatomic [Pt/Cr] multilayer stack is transformed into a uniform CrPt alloy film with L1_0 phase, which pins the adjacent 120 A CoFe layer with a pinning field of ～70 Oe and a coercivity of only 28 Oe. The hysteresis loop of this exchange biased system is almost square and the interdiffusion between the CrPt and the CoFe layers is rather small. The equivalent interface exchange energy ΔE, 0.12 erg/cm~2, is comparable to the typical value of FeMn biasing system. However, the blocking temperature, at which the exchange bias disappears, is as high as 600℃, 150℃ higher than the highest value ever reported. Since it possesses extremely good thermal stability, large exchange bias, little interdiffusion, and high corrosion resistance, the antiferromagnetic CrPt film is proposed to serve as a pinning layer for magnetoresistive devices.