Spin Dynamics In Magnetic Films

Investigations on magnetic dynamics are of great significance to both fundamental physics and technological advances.Various of modes during the collective precession of magnetic moments can be formed,depending on the structure of magnetic materials and the distribution of effective fields.These abundant magnetodynamic processes reflect the magnetodynamic properties of magnetic materials and can be regulated by a variety of means.In this dissertation,we systematically investigate variable precession modes of magnetic moments in permalloy(Py)continuous films and micro-nano structures,as well magnetic dynamics in Py and Nd based heterojunctions and magnetic multilayers.The major results are summarized as follows:1.The formation conditions and control methods of various spin precession modes in permalloy films.By studying the perpendicular standing spin wave in Py continuous films,it is found that both static and dynamic properties of Py_100-xRE_x(RE=Gd,Nd and Tb)films can be effectively controlled by dilute rare earth(RE)doping.Particularly,a 44%reduction of the exchange stiffness of Py-RE was achieved by doping with 3 at.%Nd,and about 4 at.%Tb can increase the Gilbert damping factor of Py-RE to 8.6×10^-2,which is about 12.5 times larger than pure Py.Though the investigation of various spin precession modes in Py micro-nano rectangular arrays with different sizes and separations,in-plane standing spin waves are observed.Their mode numbers and boundary pinning are further obtained by theorical fitting and micromagnetic simulation.We conclude that the boundary pinning coefficients of in-plane standing spin waves with different mode numbers are various,depending on the dynamic pinning effect of the magnetic moment near the boundary.2.Magnetic dynamics in magnetic heterojunction of Nd-based nonmagnetic metal and permalloy films.Dynamic properties of Py films are controlled by capping with Nd based nonmagnetic layers.In Py/Nd heterojunction,the Gilbert damping of Py film increases with the thickness of the Nd capping layer,and the maximum increase is more than 6 times the Py intrinsic damping.By studying the inverse spin Hall effect and samples with Cu spacer layer,we attribute the increase of Py magnetic damping caused by Nd capping layer mainly to the interface effect.Based on this special property of Nd,both the interface of Py/CuNd and the spin-orbit coupling of CuNd layer can be designed by Nd doping,and furthermore,the magnetic damping of Py is effectively controled.3.Control of interlayer spin transport in magnon valve structures.In Py/Cu/FeCoTb spin valve structure,dynamic properties of Py are affected by relative orientations of two magnetic layers.Results show that in the case of negligible static exchange coupling between two magnet layers,both of the equivalent interlayer effect and the Gilbert damping(?)of Py increase when changing the magnetic configuration of Py and FeCoTb from parallel(P)to antiparallel(AP).The value of?in AP is about five times larger than that in P configuration,indicating that the relaxation of spin current in AP configuration is much more serious than that in P configuration.Effects of the magnon interaction and the interface dissipation on magnon transmission in spin valve structure are investigated by time-resolved magneto-optical Kerr effect.Compared Py/Cu/FeCo and Py/Cu/Py spin valve structures,we demonstrate that interactions between magnons are determined by their intrinsic frequencies.Magnons with different intrinsic frequencies have strong interactions.In contrast,magnons with similar intrinsic frequencies have relatively week interactions.By studying Py/Tb/Cu/FeCo/Gd multilayer films with rare earth inset layers,we find that interfacial dissipations of magnons are increased by rare earth insertion,which can reduce the interactions between magnons indirectly.This work is important to the development of magnon valve based magnonic devices.