Enhanced perpendicular magnetic anisotropy in Co/Ni multilayers with a thin seed layer

Perpendicular magnetic anisotropy (PMA) is induced in Co/Ni multilayers when they are grown on a (111) textured Au seed layer, provided it is at least 2 nm thick. The anisotropy increases with increasing Au thickness due to improved crystallinity. Postannealing treatments of as-grown [Co(0.3)/Ni(0.6)](5) (thicknesses in nanometer) multilayers enhance the coercivity and PMA up to an annealing temperature of 250 degrees C, but higher temperatures lead to intermixing of Co and Ni which diminishes PMA. The easy axis becomes in-plane for samples annealed at 400 degrees C. The improvement in PMA in Co/Ni layers due to annealing is limited by the Au seed layer thickness. Annealing also reduces the saturation magnetization by similar to 15% due to the formation of superparamagnetic islands. Our results show that the PMA in Co/Ni multilayers can be improved by annealing up to 350 degrees C, which is required for the thermal stability of spin transfer torque memories. (C) 2010 American Institute of Physics. [doi:10.1063/1.3481452]