Study Of The Nonreciprocity Of Spin Waves And Their Mode Hybridization

The orderly precession of electron spins in magnetic materials can generate spin waves.As carriers of energy and information transmission,spin waves are smaller,faster,and have lower power consumption than traditional electronic devices.The field of spintronics has broad application prospects.Determined by the chirality of the spin precession equations,a distinctive feature of some spin waves is their non-reciprocity.Therefore,it is expected to design spin-wavebased information transmission and processing devices based on the non-reciprocity of spin waves.This dissertation mainly focuses on the non-reciprocal behavior of spin waves and their mode hybridization.Mainly through the wave vector-resolved function of Brillouin scattering(BLS)to detect spin waves in magnetic nanofilm materials and study the non-reciprocity of frequency dispersion and mode distribution.The following innovative results have been obtained:1.A giant non-reciprocal phenomenon of magnetostatic surface spin waves(MSSWs)has been discovered in double-layer magnetic films.In the Co/FeNi bilayer,the frequency of the MSSWs transmitted at the interface under the FeNi film decreases with the increase of the wave vector,that is,the group velocity is negative,and the transmission behavior is similar to the backward bulk spin wave.It was found that the frequency non-reciprocity of MSSWs at the upper and lower interfaces of FeNi films increases with the increase of the wave vector,and the maximum non-reciprocity can reach about 4 GHz.After analysis,It was found that this phenomenon is caused by the dipole interaction between the two magnetic films.2.Discovered the nonreciprocal hybridization of two spin waves in FeNi monolayer magnetic films.The transmission of MSSWs and perpendicular standing spin waves(PSSWs)was simultaneously observed in FeNi monolayer magnetic films with suitable thickness by BLS method,and the spin-wave hybridization of these two modes was realized by changing the wave vector of the surface wave.Moreover,the hybridization of the two spin waves is strongly non-reciprocal,that is,the transmission of PSSWs is suppressed at the upper interface of the FeNi monolayer magnetic film after the hybridization,and the transmission of MSSWs is suppressed at the lower interface of the film.Micromagnetic simulations and experiments confirm that this nonreciprocal hybridization is related to the thickness,saturation magnetization,and exchange constant of the material.3.Asynchronous and non-reciprocal magnon hybridization in YIG/ FeNi bilayer magnetic thin films was discovered.Hybridization of MSSWs and PSSWs was observed in YIG/ FeNi bilayer magnetic films of suitable thickness by BLS.However,due to the frequency difference of the MSSWs in FeNi due to the magnetostatic interaction of YIG,the hybridization of the upper and lower interfaces of FeNi becomes asynchronous with the increase of the wave vector.After hybridization,only MSSWs are transported at the upper interface of the FeNi film,which inhibits the transport of PSSWs.On the contrary,there is only the transport of PSSWs at the lower interface of the film,which inhibits the transport of MSSWs,that is,the hybridization produces nonreciprocity.By changing the thickness of FeNi,the wave vector during hybridization can be tuned.