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 was 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.