Research On Inverse Spin Hall Effect And Electron Paramagnetic Resonance Measurement Based On Microwave Cavity

In this thesis,we have designed a TE₀₁₁ mode resonant cavity working at 9 GHz,and built an electron paramagnetic resonance?EPR?spectrometer.We have used the DPPH to calibrate the spectrometer.And we have also used the spectrometer to study the inverse spin Hall effect in Nb-doped SrTiO₃.First,we have designed a EPR spectrometer based on the EPR principle,and then completed the design work of the magnetic field system and the resonant cavity which is the core component of the spectrometer.Using the HFSS high-frequency simulation software,we have determined the structural parameters of the TE₀₁₁ mode resonant cavity,and got a copper resonant cavity.The resonance frequency of the cavity is 8.838GHz,the return loss is-20 dB,and the Q is 12000.The cavity has been used in the EPR spectrometer.The magnetic field system consists of a permanent magnet,a DC coil,and a AC coil.The maximum static magnetic field is 3400 Oe,and the minimum sweep step is 0.036 Oe,The magnetic field system has also been used in the EPR spectrometer.We have calibrated our continuous wave EPR spectrometer with DPPH,and we have studied the effects of different system parameters such as microwave power,modulation magnetic field,and time constant on the test results.The results show that when the microwave power in the resonant cavity is from 9 dBm to 15 dBm,the square of the signal intensity is proportional to the microwave power.When the modulation current is increased from 0.1A to 0.9A,the EPR signal intensity increases,but the EPR signal intensity is not in proportion to the modulation current.And the line width of the EPR spectrum of DPPH increases.The sensitivity of the EPR system established is N_min=3.04×10¹⁴(spins·Hz^-1/2·Gauss^-1),the working frequency is 8.838GHz.The effect of doping concentration on the inverse spin Hall effect of Nb-doped SrTiO₃?Nb:SrTiO₃?was studied by using the established EPR spectrometer,where the Nb concentration was 0,0.01%,0.015%,0.028%,0.05%,0.1%,0.15%,0.2%?wt%?.The ferromagnetic resonance-spin pumping method was used to inject spins from the ferromagnetic NiFe thin film into Nb:SrTiO₃.The spin rectification voltage and inverse spin Hall voltage of the NiFe/Nb:SrTiO₃ structure were measured.The Spin Hall angle of Nb:SrTiO₃ is estimated.The results show that when the Nb doping concentration increases,the spins injected to Nb:SrTiO₃ increases,but the spin Hall angle decreases from 0.05 to 0,indicating that the spin-to-charge conversion efficiency decreases.The experimental results show that the inverse spin Hall voltage can be obtained by doping SrTiO₃ with a strong spin-orbit impurity Nb.By changing the doping concentration,the inverse spin Hall effect of SrTiO₃ can be adjusted.