Ferromagnet And Transition Metal Bilayers System: Inverse Spin Hall Effect And Nonvolatile Electrical Field Control

Spintronics,a paradigm of electronics based on the spin degree of freedom of the electron,has attracted increasing attention due to the advantages of being nonvolatile,reduced power dissipation,and increased storage density as compared to traditional electronics devices.Spintronics initially emerged as the utilization of spin-polarized currents.Recently,spintronics entered a new stage:exploration of pure spin current.In comparison with spin-polarized currents,pure spin currents are of more interest since they are accompanied by neither net charge currents nor stray Oersted fields and can therefore carry information with minimal power dissipation.Thus,it can be anticipated that pure spin currents will play a crucial role in future spin-based electronic devices.To integrate with current technology,which is mainly charge based,pure spin signals need to interconvert efficiently with charge signals.The spin and charge currents can interconvert to each other in nonmagnetic materials by means of the spin Hall effect or the inverse spin Hall effect.The conversion efficiency,typically characterized by the spin Hall angle,is thus one of the key parameters for spintronics applications.Generally,the metal materials with being strong spin-orbit interaction(like Pt,Ta etc.)has owned a relative larger values for spin Hall angle.Otherwise,the value of spin Hall angle is still inconsistent by using different measurement methods,such as non-nonlocal technique,ST-FMR and spin pumping etc.Therefore,how to obtain the accurate value for spin Hall angle and explore the new materials which has a higher spin Hall angle is vital for future applications.In traditional integrated circuits,it is convenient to use electrical means to control the storage state.Consequently,how to realize to control pure spin current by electrical field will play a crucial role in future spin-based devices applications.Due to the net charge current immune properties,the pure spin current can be carried by magnon or spin wave.As a result,it is possible to transport pure spin current for a long distance with low energy dissipation.Firstly,in this thesis paper,we introduce how to obtain spin Hall angle for ?-phase dominated Tantalum film accurately which has been predicted by theory to own a large spin Hall angle and reported by experiments.In our study,we design the relative position for sample and CPW and chose the special external magnetic field angle to eliminate the unwanted AMR signal.By growing the continuous thickness tantalum film,we can include the interface effect into the spin mixing conductance.Combining the theory model,we can obtain the spin Hall angle and spin diffusion length to be-0.0062 and 5.lnm respectively.Secondly,topological insulator materials,BiSbTeSe(BSTS),which has owned spin-momentum property for its surface state electrons and a better bulk insulating.It is expected a larger spin current and charge current conversion efficiency is occurred in its surface state.In our study,we chose the single crystal YIG as the spin current injected layer.Due to the weak interaction between layers for BSTS,we can obtain high quality BSTS layer by using mechanical exfoliation method as the spin current detected layer.By performing the spin pumping experiment,we can observe a large inverse spin Hall effect voltage induced by BSTS.At low temperature range,we find the inverse spin Hall effect voltage is increased which indicates the surface state gives a dominate contribution for the detected voltage.Thirdly,to integrate the spin current transport with modern electronic industry,it is popular demand to control spin current by electrical method.Here,due to electrical field controlled of ferroelectric material PMN-PT,we grow high quality YIG film on PMN-PT substrate with suitable deposited condition as being the spin current injected layer.Then we grow Pt and Cu layer sequently as the spin current detected layer.Combining the spin pumping experiment and magnetoelectric coupling,we realize nonvolatile electric field control of ferromagnetic resonance field and inverse spin Hall effect in Pt/YIG/PMN-PT heterostructure.Fourthly,how to transport the spin current for a long distance effectively is one of the cornerstones for the future spin-based device.It has attracted more and more attentions and widely researched recently.Here,in vertical structure Pt(5nm)/non-crystalline YIG(80nm)/Pt(5nm)tri-layers,we inject the charge current into the bottom Pt layer and it can be converted spin current by using spin Hall effect.Then these spin current will be accumulated at Pt/non-crystalline YIG interface.Under this thinner thickness limited for non-crystalline YIG,the spin current will diffuse through the whole non-crystalline YIG layer and arrive the second interface between the top Pt layer and non-crystalline YIG layer.Finally,these injected spin current will be converted detectable voltage by inverse spin Hall effect.As a comparison,we performance the same measurement in Pt(5nm)/non-crystalline YIG(80nm)/Ta(5nm)tri-layers and the detected voltage's sign is changed due to a negative spin Hall angle for Ta.It demonstrates the detected voltage is originated from the spin related signal not rather the parasitic signal.It indicates the non-crystalline YIG can be as an effective and alternative material for spin current transport.