Correlating spin freezing and magnetic properties in [Co/Ni]n/PtMn multilayers

Abstract

Exchange-coupled ferromagnetic/antiferromagnetic (FM/AF) bilayers are widely used in spin valves, magnetic tunnel junctions and spin–orbit torque devices. While most studies focused on AF layers exchange coupled with single FM layer, the exchange interaction with FM multilayer were not well understood. In this work, [Co/Ni]n/PtMn multilayers with different PtMn thickness were prepared. Polycrystalline face-centered cubic Co, Ni, and PtMn phases were evidenced by the grazing incidence x-ray diffraction measurements. At room temperature, the [Co/Ni]n/PtMn multilayers show similar soft ferromagnetism as the reference [Co/Ni]2 layers. Reducing the temperature results in broadening of the hysteresis loops, and exchange bias was not observed until 100 K. Temperature-dependent DC magnetization and AC susceptibility revealed blocking temperatures of 210–240 K and a spin freezing temperature of 140 K. This work has revealed the temperature evolution of exchange interaction in [Co/Ni]n multilayer interfacing with A1-phase PtMn. The results are important for understanding the physical process of the establishment of exchange coupling in various FM/AF interfaces.