Research Of Inverse Spin Hall Effect In Doped STO

With the development of spintronics,ISHE in non-magnetic metals and various alloy materials has been widely studied.Spintronic devices with a series of advantages such as low power consumption,high storage density,and fast response speed have also attracted a lot of attention.In this paper,the spin-flow is generated and detected by the spin pumping-inverse spin Hall effect method.First,the test method of V_ISHE signal is studied.Then,the related research on ISHE in doped STO is carried out.The conversion of this tunable spin-charge current in doped STO provides more possibilities for the further development of spintronic devices.In this paper,the relationship between film width and V_SRE signal in single-layer NiFe film is studied.It is found that when the film length is 8 mm and the width is 40μm,the V_SRE signal is weaker than the detection limit,and then the magnetron sputtering method is used to deposite a NiFe/Ta bilayer film and a NiFe film with a width of 40μm on the SiO₂ and doped STO substrates respectively.For the NiFe/Ta bilayer film,the method of reducing the V_SRE signal below the detection limit can directly measure the V_ISHE signal with symmetric lines in the sample.The test results also show that this test method is widely applicable to FM/NM bilayer of specific size.A method is proposed for the strip type bilayer structure to effectively increase the measured V_ISHE signal intensity,which is confirmed in the experiment.When studying the method of reducing the V_SRERE signal below the detection limit in the NiFe/Nb:STO bilayer structure,it was found that when the NiFe width is 40μm,the measured V_SRE signal intensity can be effectively reduced,but due to the conductivity of the doping STO substrates causes the V_SRE signal in the NiFe/Nb:STO bilayer structure to be incompletely eliminated.The measured voltage signal still contains significant antisymmetric components.Therefore,the flip test method widely used for separating V_SRE and V_ISHE signals in FM/NM bilayer films is introduced.This method is also well suited for NiFe/Nb:STO bilayer structure,so in the latter research,the flip test method is used to separate the V_SRE and V_ISHE signals in the NiFe/Nb:STO bilayer structure.This paper focuses on the ISHE in doped STO.NiFe films were deposited on the undoped and doped STO substrates by magnetron sputtering.The curves of V_SRE signal and V_ISHE signal with applied magnetic field were separated by flip test method.The results show that in the undoped STO substrate,the voltage curves obtained before and after the flipping are basically the same,which is the V_SRE generated by the SRE of NiFe film.By fitting the V_SRE curve at different frequencies,we can obtain:the effective saturation magnetization 4πM_s of the NiFe film is 7694 Gs,H_k is 3.5 Oe,and the damping coefficientαis 0.018.For different Nb-doped samples,significant spin-charge current transitions are detected in samples with doping concentrations of 0.015,0.028,0.05 and0.1,and the magnitude of V_ISHE decreases with doping concentration.However,the V_ISHESHE was not detected in the samples with doping concentrations of 0.15,0.2 and 0.25,and the test curves before and after the flipping are basically the same.In addition,the relationship between the amplitudes of V_SRE and V_ISHE signals at different frequencies is studied.It is found that their trends with frequency are basically the same,indicating that their changes with frequency are caused by the test fixture and are independent of the sample itself.In addition,the magnetic parameters of the corresponding samples can be obtained by fitting the V_SRE curves.The effective saturation magnetization 4πM_s is about7600 Gs,and the H_k is about 4 Oe.The damping coefficientαof the sample detecting V_ISHE was greater than that of the sample without V_ISHE detected.Finally,the samples with different doping concentrations were annealed.The results show that annealing can effectively improve the magnetic properties of the films,but it has no essential effect on the conversion of spin-charge current.