Inter-granular exchange coupling and magnetic anisotropy of Ta/Ru/Co-23 at%Pt perpendicular thin films with different Ru underlayer thicknesses

In the present work, a series of Ta/Ru/Co-23 at%Pt thin films with varied Ru underlayer thicknesses were fabricated by magnetron sputtering. All of the films show c-axis preferred orientation perpendicular to the film surface. The drop of c/a ratio and lattice expansion of Co–Pt layer with the increase in Ru underlayer thickness was revealed by X-ray diffraction(XRD). The coercivity of the Ta/Ru/Co–Pt thin films increases drastically with Ru underlayer thickness increasing, due to the enhancement of effective magneto-crystalline anisotropy constant and exchange decoupling of magnetic nano-grains. The enhancement of effective magneto-crystalline anisotropy constant is ascribed to the lattice deformation of Co–Pt layer by mismatching the Ru layer and Co–Pt surface.Moreover, the exchange decoupling of magnetic nanograins is attributed to the further isolation of magnetic nano-grains.