Magnetic Properties And Thermal Stability Of Co / Ni Multilayers

In this paper, the spin transfer torque magnetic random access memory (STT-MRAM) is introduced, the application prospects and some research progresses are described, and [Co/Ni]N multilayers (MLs) with perpendicular anisotropy (PMA) are manufactured. By changing parameters of the Ta (3.0nm)/Cu (tCu)/[Co (0.29nm)/Ni (0.65nm)N/Ta (3.0nm) multilayers and introducing post annealing treatment, the magnetic properties are modulated and performances of the materials are improved.Based on the optimized single layer thicknesses of Co, Ni in the MLs, periodic numbers (N) were changed to investigate the function of interface. Multilayers with lower N have less PMA owing to the not enough interfaces, and PMA increases with N. But the magnetic hysteresis loop for the structure with N in excess of10exhibits a bow-tie shape due to the formation of multi-domains, which may cause a significant drop of the remanence ratio. Multilayers with different seed layers performance different PMA, and perpendicular coercivity increases when the thickness of seed layer increases. By Time-resolved MOKE, ultra-fast spin dynamics of [Co/Ni]N multilayers were obtained.Post annealing with moderate temperature could improve interface effect of Cu/Co, Co/Ni, thus enhance the PMA. The thermal stability study shows that the MLs with strong PMA are more thermally stable. As the annealing temperature further increases, atoms (Co, Ni, Cu, Ta) intermixed, interface effect weakened, nonmagnetic depinning sites increased because of the appearance of nonmagnetic atoms (Cu, Ta) and the increased voids in the magnetic layers. For reasons above mentioned, the saturation magnetization and PMA decreased, the perpendicular coercivity increased. Our results indicate that the effect of seed and capping layers should be taken into account when designing practical devices.