Perpendicular exchange bias in nickel/antiferromagnetic bilayers

Exchanged biased Ni films with perpendicular magnetic anisotropy is studied using bilayers of 4 nm thick Ni and a thin antiferromagnetic (AF) film. The AF materials used were FeMn, IrMn, NiMn, and PtMn. Results show that the exchange bias field is largest for FeMn, considerably smaller for IrMn and NiMn and zero for PtMn. The difference in exchange bias field between FeMn and IrMn is explained in terms of film texture, grain size, and interface roughness. The very low (NiMn) and zero (PtMn) perpendicular exchange bias measured on the Ni/AFM bilayer is due to the fcc film structure. An attempt to anneal the Si(001)/50 nm Cu/4 nm Ni/AFM/5 nm Cu films at 200 °C resulted in severe mixing between the Cu and Ni layers which destroyed the perpendicular magnetic anisotropy.