Study On Perpendicular Magnetic Anisotropy And Domain Structure Of Co/Ni Multilayers

More recently,magnetic multilayers with perpendicular magnetic anisotropy?PMA?have attracted great interest due to the promising application in magnetic random access memories?MRAM?.Co/Ni multilayers exhibit tunable perpendicular magnetic anisotropy,high spin polarization and low intrinsic damping,making them attractive for use in spin current devices.Therefore,researches on perpendicular magnetic anisotropy and domains of Co/Ni multilayer are of great value.In this paper,Co/Ni multilayers with Au-buffered were first prepared,and then the effect of the thickness of buffer layer Au,the thickness of magnetic layer Ni,the bilayer repeats and temperature on the static and dynamic magnetic properties were studied.When the thickness of the buffer layer Au is greater than or equal to 5 nm,the multilayers have perpendicular magnetic anisotropy.Specifically,when the thickness ratio of the Ni/Co layer is 2/1,the multilayers have the strongest perpendicular magnetic anisotropy,and the Co/Ni interface anisotropy constant K_s is about 0.28 mJ/m².As the bilayer repeats N increases,the coercive force H_c and effective perpendicular magnetic anisotropy constant K_eff decrease.And the saturation magnetization M_s increases.For Co/Ni multilayers with N?7,sharp magnetization switching is observed.In contrast,the loop of Co/Ni multilayers with N?9 have a bow shape,showing multi-domain structure.It can be seen from FMR?Ferromagnetic Resonance?measurements that intrinsic Gilbert damping is inversely proportional to N.The smallest?_int is found for Co/Ni multilayers with N=11,and the value is 0.016.When the multilayers was deposited on a lithium niobate substrate,the perpendicular magnetic anisotropy reduced.The deposition order of Co and Ni also has an effect on the perpendicular magnetic anisotropy.Compared with the Au/[Ni/Co]structure,the Au/[Co/Ni]structure multilayers have stronger perpendicular magnetic anisotropy.At low temperatures,as the temperature decreases,the coercive force H_c increases,and the perpendicular magnetic anisotropy increases.When the buffer layer Au is replaced with Pt,only 2 nm Pt is required,and the multilayers have perpendicular magnetic anisotropy,which is thinner than that required when Au is used as the buffer layer.This is because the spin-orbit coupling of Pt is strong.By changing the thickness of magnetic layer Ni,it indicates that the magnetic domain evolution during magnetization reversal is closely related to the perpendicular magnetic anisotropy of multilayers.As the bilayers repeats N increases,the coercive force H_c decreases.The perpendicular magnetic anisotropy decreases.And the saturation magnetization M_s increases.The size of the magnetic domain decreases rapidly in exponential form.After vacuum annealing,it is obvious that annealing at appropriate temperature can improve the interface effect and increase the perpendicular magnetic anisotropy.Owing to the multilayer with a large N has more interfaces,the sample can withstand higher temperature annealing and has higher thermal stability.