Tuning the perpendicular magnetic anisotropy of [Co(0.3nm)/Ni(0.6nm)]20 multilayer thin films

Abstract

In this work, series of thin films of [Co(0.3nm)/Ni(0.6 nm)]20 multilayers have been prepared on Si substrate under four conditions; (i) as-prepared film (ii) inserting Cu under layer (iii) in-situ annealing of Ta/Cu under layer (iv) in-situ annealing combined with post annealing, by employing a magnetron sputtering. The as-prepared film exhibits isotropic behavior, whereas multilayers deposited under other conditions exhibit perpendicular magnetic anisotropy (PMA). The values of coercivity, saturation magnetization, squareness are found to be maximum for the case of as-prepared Co/Ni multilayers film. However, the value of effective PMA constant is found to enhance and it is estimated to be 9.5 × 104, 12.7 × 104, 15.8 × 104 J/m3 for multilayers with Cu-underlayer, with in-situ annealing, and in-situ combined with post-annealing respectively.The observed PMA is explained in a correlation with surface topography and roughness studied by atomic force microscopy images, and crystalline orientation as demonstrated by x-ray diffraction pattern. Thin films of Co/Ni multilayers with Cu underlayer, in-situ annealing of Ta/Cu underlayer, and in-situ combined with post-annealing have relatively smoother and homogeneous surface and with a crystalline orientation of Co/Ni along <111>. This combined effect is likely to help in promoting PMA in these films. The magnetization reversal in these films is achieved by domain wall propagation.