Research On Spin Hall Effect,Anomalous Hall And Nernst Effect In Magnetic Metal Thin Films

The development of spintronics has contributed tremendous impetus to the in-depth exploration of basic science and the vigorous development of the information industry.Among them,magnetic metals including ferromagnetic metals and antiferromagnetic metals were used as the main research object since the beginning of spintronics to promote the development of spintronics.In recent years,a number of emerging branches have joined spintronics and have become more and more important,such as the spin Hall effect?SHE?in heavy metals and spin-orbit-torque?SOT?magnetization switching,and the effect of magnon transport in magnetic insulators caused by temperature gradients like magnon valve effect?MVE?.They provide new perspectives on industrial development and scientific research for spintronics research.In this aspect,if we look at magnetic metals,we will find that there are many possible connections between the spin Hall effect,anomalous Hall effect?AHE?,and anomalous Nernst effect?ANE?in ferromagnetic or antiferromagnetic metals and the novel spin quantum effects such as electrical or thermal spin injection,SOT and magnetization switching,and electrical transport in two dimensional materials,which has great value of further interpretation and exploration.Around this theme and on the basis of trying to summarize the existing theoretical system and research methods,this dissertation adopts mature thin film deposition methods like magnetron sputtering or molecular beam epitaxial,graphical methods like ultraviolet lithography and argon ion etching,as well as electrical transport test methods like DC four-probe or AC harmonic method.The SHE,AHE and ANE of antiferromagnetic metal IrMn and Cr,ferromagnetic metal NiFe,two-dimensional ferromagnetic metal Fe₃GeTe₂ have been studied and explored in this dissertation.The main content of this dissertation mainly includes the following four items of innovation:?1?Through spin injection and relaxation,we detected the spin relaxation time as high as the order of 10 ps and its temperature dependence of the antiferromagnetic metal in IrMn?Ta,Pt?/MgO/Co Fe B/Ta/Ru stacks.Based on the dependence of spin relaxation time on temperature,we could reveal the scattering mechanism in antiferromagnetic metal.Thus it provides a reference for the principle of magnetic moment control and spin current generation.?2?Based on the SHE tunneling spectroscopy,the spin-fluctuation-enhanced spin Hall effect in the antiferromagnetic metal Cr in Cr/MgO/Fe/Au is determined.Compared with heavy metal alloys containing magnetic impurities,antiferromagnetic metals can provide local magnetic moments without showing spontaneous magnetization outside,which can significantly reduce mutual demagnetization field interference between device units,making sample preparation simpler.The film is fabricated into 6?m×6?m injection junction matrix.It is found that near the antiferromagnetic-paramagnetic transition temperature,the spin Hall conductance gain a considerable increase with a spin Hall angle of 0.15 and an enhancement rate of 100%at 200 K which reaches the advanced level in known metal materials.This gain comes from the enhancement of the interaction between the conduction electrons and the local magnetic moment's spin fluctuation.?3?In the NiFe/Cu/NiFe/Co/IrMn/Pt sandwich structure,the in-plane current is applied to realize the in-plane magnetization switching due to AHE with the critical switching current density of 1 MA/cm².The switching behavior can be explained by the spin-orbit theory with the spin current of?-m _R?m _R×E?originated from AHE.Then switching chirality is also tunable by engineering the magnetization of the reference layer.At the same time,the structure has been proved to have the feasibility at low temperature to 10 K and in two-end structure,also in Co/Au/Co spin valve.?4?AHE and ANE are observed in the magnetic two-dimensional metal Fe₃GeTe₂with perpendicular magnetic anisotropy deposited by heating evaporation at high vacuum with low deposition rate.By studying anomalous Hall angle,Seebeck coefficient and anomalous Nernst coefficient and their temperature dependences,a scaling law based on the Mott relationship is established.Compared with the simple Mott relation,the scaling law has advantage of showing the synergy of anomalous Hall angle and anomalous Nernst coefficient.The anomalous Nernst coefficient maximum is calibrated as 0.28?V/?KT?and the thermoelectric efficiency factor,which can provide a reference for the research on the thermoelectric effect of the two-dimensional magnetic conductor in the future.