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 Co x Fe 80-x B 20 (x= 60, 40, 20) as spin-polarizing layers (SPL) in order to investigate the composition of the CoFeB-SPL on the magnetoresistance (MR) in Co/Pd multilayers-based pseudo-spin-valves (PSV) with perpendicular magnetic anisotropy (PMA). In both soft layer (SL) and hard layer (HL), 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 SPL thickness in the as-deposited case, irrespective of the CoFeB atomic composition and M s. However, interesting behavior is observed when the films were annealed. Although GMR degradation is expected after annealing, a peak of GMR was observed after post annealing the samples at 250 ºC. 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 M s. 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, Co 60 Fe 20 B 20 polarizer shows a stronger PMA due to its lower M s , leading to the weaker demagnetization. In addition, this study also indicates that the crystallographic texture of Co/Pd multilayers plays a role in the MR.