Effects of Co80Fe20 insertion layer on perpendicular exchange bias characteristics in [Pd∕Co]5∕FeMn bilayered thin films

Abstract

Effects of Co80Fe20 insertion layer on the perpendicular exchange bias characteristics in [Pd∕Co]5∕FeMn bilayered thin films have been investigated by changing the Co80Fe20 insertion layer thickness. Hysteresis loops for both in-plane and perpendicular to the film plane were measured by using a vibrating sample magnetometer and an extraordinary Hall effect. It was found that the thin Co80Fe20 insertion layer was very effective in improving the perpendicular exchange bias characteristics in [Pd∕Co]5∕FeMn bilayered thin films. By increasing Co80Fe20 insertion layer thickness from 0to1.24nm, the exchange bias field was significantly increased up to 332Oe and then decreased down to 60Oe, while the pinned coercivity was monotonically decreased. The effective magnetic anisotropy was kept at positive up to 0.6nm thick of Co80Fe20 insertion layer. It was experimentally confirmed that the perpendicular exchange bias field was promisingly larger than the pinned coercivity when the Co80Fe20 insertion layer had the thickness in the range between 0.37 and 0.56nm. The significant increase of the perpendicular exchange bias field and the reduction of pinned coercivity after inserting Co80Fe20 thin films are thought to be attributed to the modification of interfacial roughness between the FeMn and adjacent top Co layers and the stress-induced change of perpendicular magnetization direction of the top Co layer, which is adjacent to FeMn layer.