Magnetic Dynamics Of Polycrystalline YIG Film And Artificial Spin Ice

Spintronics,an emerging research field in physics,is an interdisciplinary field that combines magnetism and microelectronics.Spintronics is focusing on the role of spin rather than charge in solid-state physics.The manipulation of spin can develop promising novel electronic devices.Compared with traditional semiconductor devices,spintronic devices have several advantages,e.g.,faster processing speed,higher integration density,and lower energy consumption.In recent years,with increasing interest in exploring new technology and mechanism to develop next-generation information processing and storage devices,spintronic materials and nanodevices have attracted more and more researchers' attention.Yttrium iron garnet(YIG)is a ferromagnetic material with ultra-low damping factor and electrically insulating,which is considered to be an ideal material for spin-wave-based devices.At present,single-crystal YIG film has been intensively studied in the field of spintronics,e.g.,spin pumping,spin Hall magnetoresistance(SMR),spin-wave excitation,transmission and detection.Until now,most YIG film was grown on the high costly single-crystal substrate gadolinium gallium garnet(GGG)due to they have the excellent lattice matching.Therefore,the single-crystal YIG film grown on GGG substrate is easy to obtain the best performance close to the bulk.However,modern semiconductor technology and devices are mostly based onsilicon wafer,and GGG substrate is too expensive to manufacture compared to silicon,which will obstruct the development of spintronics devices.In this project,we tried to obtain high-quality YIG films with less than 100 nm on Si substrate by radio frequency magnetron sputtering at room temperature,followed by ex-situ post-annealing method to crystallize YIG in air.We figured out the optimal annealing conditions based on the substantial studies of the surface morphology(SEM,AMF),XRD,and magnetization characterizations.We also studied thickness-dependent magnetization properties and found magnetization properties degeneration behavior of YIG film with decreasing thickness.Subsequently,we deposited a heavy metal layer Pt on the top of annealed YIG film,and investigated spin-change conversion coefficiency of Si/Si O2/YIG/Pt system by performing spin pumping experiments.We found that the polycrystalline YIG/Pt bilayer has a considerable spin mixing conductance compared to previously reported single-crystal YIG and Py systems.The electrical detection of spin-wave in polycrystalline thin YIG films deposited on Si substrate is an important step in the development of YIG-based magnonics with COMS technological processes.Additionally,we investigated the magnetoresistance and magnetization dynamics of the artificial kagome spin-ice(ASI)structure made of Permalloy.The magnetoresistance measurements reveal that the dipole field related to kagome shape spin configuration causes several abnormal behaviors in the magnetization reversals.Four distinct field-frequency dispersion curves obtained by ferromagnetic resonance experiments show rich spin-wave spectra,suggesting kagome ASI exhibits several different magnetization configurations induced by spin frustration.These observed results and conclusions are further confirmed by spatial resolution spin-wave spectra,which can be accessed by micromagnetic simulation.Combining FMR of nanostructure and simulation techniques,we find that the ASI has abundant spin configurations under its coercive field,providing a platform for us to explore the rich spin-wave dynamics of the artificial geometric frustrated magnetic systems in the microwave regime.