Theoretical Calculation Of Gilbert Damping In Magnetic Thin Films

The dissipation phenomena in magnetic materials have attracted much attentions,in which the Gilbert Damping is an important parameter to scale the dissipation.In magnetic memory devices constructed by magnetic thin films,how to adjust the Gilbert Damping becomes particularly important.Especially the spin-orbit coupling makes the physics of multilayer systems more complex and interesting when heavy metals are involved.The Gilbert damping ? of Co|X(X represents different materials,X=Pt,Pd,Ni)multilayers are calculated,Co|Pt and Co|Pd multilayers are in good agreement with the experiments,but there is a large discrepancy between calculations and experiments of Co|Ni multilayers.The First Principle calculation concludes this is caused by an interface enhanced damping induced by capping layers in experiments.Spin pumping theory can describe this enhancement properly: the precessing magnetization "pumped" a spin current into adjacent nonmagnetic layers,which brings an extra term to magnetization dynamic LLG equation.This enhancement is mainly affected by X layer thickness,which increasing monotonically with X layer thickness.Co|Ni multilayers has a large perpendicular magnetic anisotropy,thus we explore the damping of Co|Ni multilayers in no contact with X,results show it rises up with the increasing Ni thickness.This trend give rise to the increasing spin-orbit coupling with increasing Ni thickness.Neither case is sensitive to temperature.In addition,the quantum well states of Co monolayer from 2 to 8 layers are systematically studied.Both damping and density of states exhibit oscillations when the thickness of Co increases layer by layer.Our results show that this oscillation originates from electrons with majority spins of Co monolayer.This oscillation can be well explained by phase accumulation theory: the phase accumulation generated by the Bloch state propagating through a film must be an integer multiple of 2 .It is interesting to note that damping is anisotropic when the film is 3 layers thickness.We also observe the anisotropy of it and explore the(111),(11(?))and(1(?)0)crystal plane.The results reveal that(11(?))and(1(?)0)crystal plane exhibit the same 2 fold rotational symmetry as crystal,but(111)crystal plane has a different symmetry from crystal.