Spin Pumping And Interface Properties Of YIG Film

Spintronics is about the manipulation of the spin degree in solids,such as spin polarization,spin dynamics,spin transport,and the detection of spin polarized eletrons.It has attracted great attention because of potential application in information storage.Recently,considerable attention has been focused on the study of genertation,transport and detection of pure spin current.Spin pumping is an important mechanism for the generation of a pure spin current in nonmagnetic conductors.The inverse spin Hall effect can subsequently convert this spin current into a detectable charge current.These two effects are widely used to detetmine the spin Hall angle of various metarials by different reseach groups.Among these studies,yttrium iron garnet(YIG),a magnetic insulator,is widely used as a spin injection layer in spin pumping experiments.In this thesis,we have grown high quality YIG films by pulsed laser deposition.And we carefully investigated the dc voltage generation in the heterostructure of YIG/Pt and YIG/PEDOT:PSS under the ferromagnetic resonance and/or spin-wave excitation condition.We also investigated the interface properties of YIG/Pt.(1)We have experimentally and theoretically investigated the dc voltage generation in the heterostructure of Pt and yttrium iron garnet under the ferromagnetic resonance.Besides a symmetric Lorenz line shape dc voltage,an antisymmetric Lorenz line shape dc voltage is observed in field scan,which can solely originate from the spin rectification effect due to the spin Hall magnetoresistance.The angular dependence of the dc voltage is theoretically analyzed by taking into account both the spin pumping and the spin rectification effects.We find that the experimental results are in excellent agreement with the theoretical model,further identifying the spin Hall magnetoresistance origin of the spin rectification effect.Moreover,the spin pumping and the spin rectification effects are quantitatively separated by their different angular dependence at particular experimental geometry.(2)We clarify the physical origin of the dc voltage generation in a bilayer of a conducting polymer film PEDOT:PSS and a micrometer-thick magnetic insulator Y3Fe5O12(YIG)film under the ferromagnetic resonance and/or spin-wave excitation condition.The previous attributed mechanism,the inverse spin Hall effect(ISHE)in the polymer[Nat.Mater.12,622(2013)],is excluded by two control experiments.We found an in-plane temperature gradient in YIG which has the same angular dependence with the generated voltage.Both vanish when the YIG thickness is reduced to a few nanometers.Thus,we argue that the dc voltage is governed by the Seebeck effect in the polymer,where the temperature gradient is created by the nonreciprocal magnetostatic surface spin wave propagation in YIG.(3)Spin wave eigenmodes in YIG thin films has been investigated by means of inverse spin Hall effect(ISHE).The spin waves in the YIG layer drives spin pumping,generation of spin currents from magnetization precession,and the pumped spin current is converted into a charge current by ISHE in the Pt layer.Besides spin wave eigenmodes in the lateral dimensions,the perpendicular standing spin waves are observed.The exchange constant of YIG can be obtained by fitting the dispersion relation of PSSW.The experimental results indicate that spin pumping provides a new method of very high accuracy to study the detail of spin waves.(4)We also investigated the interfacial properties of YIG/Pt.We find that the growth of metal Pt on YIG thin films reduces the magnetic moment of YIG at the interface.Through the measurement of X-ray magnetic circular dichroism,we found that the growth of Pt has an influence on the electronic valence of Fe irons in YIG,and the trivalent Fe ions of YIG undergo charge transfer with Pt to generate a small amount of divalent Fe ions,which should cause a decrease in YIG magnetism.We consider that the change of magnetic properties of YIG by depositing Pt will greatly affect the spin injection efficiency.