CoFeB spin polarizer layer composition effect on magnetization and magneto-transport properties of Co/Pd-based multilayers in pseudo-spin valve structures

Abstract

In this work, we used CoxFe80-xB20 (x = 60, 40, 20) as spin-polarizing layers (SPLs) in order to investigate the composition of the CoFeB-SPL on the magnetoresistance in Co/Pd multilayers-based pseudo-spin-valves (PSVs) with perpendicular magnetic anisotropy (PMA). In both soft layer and hard layer, the PMA was achieved by tuning the interface anisotropy and bulk anisotropy between SPL and Co/Pd multilayers. For all the films, giant magnetoresistance (GMR) was found to decrease with increasing SPL thickness in the as-deposited case, irrespective of the CoFeB atomic composition and saturation magnetization (Ms). However, interesting behavior is observed when the films were post annealed. Although GMR degradation is expected after annealing, a peak of GMR was observed after post annealing the samples at 250 °C. This peak is stronger for the samples with thicker SPLs than those with thinner SPLs. Nonetheless, further increase in annealing temperature causes a reduction in GMR which is found to be larger in Co rich atomic composition samples with a lower Ms. In the case of thicker CoFeB SPL (15 Å), the magnetization of overall composite (Co/Pd)/CoFeB soft layer appears to be canted from out of plane direction. Among the three compositions investigated, Co60Fe20B20 polarizer shows a stronger PMA due to its lower Ms, leading to the weaker demagnetizing field. In addition, this study also indicates that the crystallographic texture of Co/Pd multilayers plays a role in GMR of PSV stack structures.