Cone magnetization state and exchange bias in IrMn∕Cu∕[Co∕Pt]3 multilayers

Abstract

The effects of a Cu interlayer on the perpendicular exchange bias in IrMn∕Cu∕[Co∕Pt]3 multilayers were investigated by focusing on the correlation between the exchange bias and the magnetic anisotropy. The in-plane magnetization hysteresis loops were interpreted in the framework of a phenomenological model based on the coherent magnetization rotation, indicating that the easy magnetization axis makes an angle of approximately 15° with the normal of the IrMn∕[Co∕Pt]3 film. This angle decreases with the introduction of the Cu spacer thickness in the IrMn∕Cu∕[Co∕Pt]3 system, indicating that the Cu interlayer leads to a predominant perpendicular anisotropy. Although a maximum of the out-of-plane anisotropy is found for Cu layer thickness between 4 and 5Å, the maximum of the perpendicular exchange bias was found at 3Å of Cu, which could be attributed to the interplay between two effects, mainly the increase in the effective perpendicular anisotropy with the Cu spacer thickness due to the reorientation of the Co moment toward the normal to the film’s plane direction, and the exponential decrease in the ferromagnet/antiferromagnet exchange coupling (and, consequently, of the exchange bias shift field) with the Cu interlayer thickness.