Research On The Ferromagnetic Resonance And Spin Wave Resonance Characteristics Of YIG High-frequency Soft Magnetic Thin Films

Electrons have both charge and spin properties.With the development of electronic devices towards integration and miniaturization,the problem of high power consumption is becoming more and more serious.Traditional devices based on charge property can no longer meet the requirements of development,and Moore’s law is no longer applicable,thus using the spin property to realize data storage,transmission and processing has become a research hotspot in recent years.Ferromagnetic resonance（FMR）and spin waves are the main research contents of magnetization dynamics.Compared with electromagnetic wave,spin waves exhibit a diversity of dispersion characteristics,and their wavelength can be decreased to the nanoscale at the microwave frequency range.Moreover,spin waves are free of Joule heat dissipation.The research on spin waves also promotes the study of spin current generation,transport and detection.Among these studies,yttrium iron garnet(Y₃Fe₅O₁₂,YIG),a magnetic insulator with extremely low damping,is one of the best materials for the study of FMR and spin waves,and is widely used in the study of spintronics.In this thesis,we prepared high quality YIG targets and YIG films,and systematically investigated the FMR and spin-wave propagation properties of YIG films.The main results of this thesis are listed as follows:（1）High quality YIG targets were prepared by solid-state reaction,and the effect of sintering temperature on the YIG targets was investigated.The single phase YIG targets with high density,uniform crystalline grain size,few stomas,and no secondary growth,were sintered under the conditions of pre-sintering temperature 1100°C,sintering temperature 1350°C for 6 hours.High quality YIG films were deposited on gallium gadolinium garnet(Gd₃Ga₅O₁₂,GGG)substrates with different crystal directions by pulsed laser deposition（PLD）using self-made YIG targets.The effects of oxygen pressure and deposition time on the microstructure and magnetic properties of YIG films were explored for optimizing the growth conditions.It is revealed that the optimal soft magnetic properties of YIG films can be obtained under oxygen pressure of 5 Pa at deposition temperature of 750°C with 3 Hz laser frequency.The effect of crystal orientation of YIG films on the structure and magnetic properties were studied.In addition,the frequency dependence of FMR linewidth was studied by FMR spectrometer under the field-scan and frequency-scan modes.（2）The propagation of magnetostatic spin waves in micron-thick yttrium iron garnet（YIG）films was studied with the applied magnetic field along the three principal directions.The spin wave mode are the Damon-Eshbach,backward volume and forward volume spin waves,respectively.Spin-wave transmission spectra were measured by a waveguide with input and output microwave microstrip antennas.The input antenna is used to excite spin waves at one edge of the film,and the output one is used to receive the spin-wave signal that goes through the film and reaches the opposite edge.From spin-wave transmission spectra,the spin-wave dispersion relation,group velocity,and their dependence on magnetic bias field strength were systematically gauged for three modes of spin waves.By changing the distance between two microstrip antennas,the effect of the microstrip antennas on the spin-wave propagation is studied.The non-reciprocity of Damon-Eshbach spin waves has also been observed.（3）The effect of out-of-plane magnetization depinning on the resonance frequency shift（?1）)was investigated for 3-μm YIG films grown on GGG（111）substrates by liquid-phase epitaxy.It is revealed that the FMR and spin wave propagation exhibit a very slow relaxation with relaxation timeτeven longer than one hour under an out-of-plane external magnetic bias field.The?1)span of 15.15-24.70 MHz was observed in out-of-plane FMR and forward volume spin waves.Moreover,the?1)andτdepend on the magnitude of magnetic field.The?1)can be attributed to the increase of out-of-plane magnetization,caused by the depinning of magnetic moments from the pinning layer at the YIG/GGG interface.The thickness of pinning layer can be estimated as 9.48 to 15.46 nm according to the frequency shifting.These results indicate that?1),caused by the interface moment depinning,should be addressed in the design of microwave and spin wave devices.