Current Induced Spin-Orbit Torques In Two Dimensional ZrSe₃ Based Heterostructure

Spintronics is an interdisciplinary subject that utilizes both the charge and spin properties of electrons.Spintronic devices,such as magnetic random access memory（MRAM）and logic devices,have great potential in future efficient data storage and computing technologies,which have attracted extensive attention in modern spintronics research.Current induced magnetodynamics,which relies on the effective manipulation of the magnetic moments by the spin current,results to the low performance and high energy consumption of spintronics devices including MRAM.Researches have found that spin-orbit torque（SOT）generated by pure spin current can be used in low-power,high-density,and fast magnetization switching.Therefore,building systems with high charge to spin efficiency is the core technical direction of new spintronic devices in the future,which is also a hot issue in the field of modern spintronics research.Most of the studies focusing on spin-orbit torques are performed on the multilayer composite film system.Traditional spin source materials generally use heavy metals with strong spin-orbit coupling（SOC）.Meanwhile,the high-quality soft magnetism is often selected for the magnetic layer.However,due to the limitation of the charge-spin conversion effectively in traditional heavy metals,it is urgent to develop new spin source material systems that can produce higher SOT efficiency.Among them,two-dimensional materials（2D）with special lattice structures and rich interface properties,provide an ideal platform to develop high-performance SOT devices.Based on the above background,we carried out a series of magnetodynamic spin-orbit torque studies on the nonmagnetic layer/ferromagnetic layer（NM/FM）heterostructures.Two-dimensional semiconductor ZrSe₃.is chosen as the NM layer due to the large SOC and the broken crytal symmetry.Nickel-iron alloy(Ni₈₀Fe₂₀,Py)is chosen as the ferromagnetic layer,whose easy magnetization direction is in the film plane and the resonance field is relativelt low at high frequency.The main research results are summarized as follows:1.Firstly,we fabricate high-quality ZrSe₃（7.6 nm）/Py heterostructure device with clear boundary by mechanical exfoliation,magnetron sputtering and micro/nano-fabrication.Compared with Pt/Py,the Gilbert damping of the ZrSe₃（7.6 nm）/Py heterostructure is very small,indicating the high uniformity of the Py film grown on ZrSe₃.At the same time,as semiconductor,ZrSe₃has an impedance mismatch with the ferromagnetic Py,which leads to the generation of an interface barrier.Therefore,it is difficult to inject spin current from Py into ZrSe₃layer,and the contribution of the interface spin pumping effect on the magnetization damping factor is approximately zero.Furthermore,we found that the heterostructure system exhibits an out-of-plane damping-like torque due to the symmetry breaking of the ZrSe₃crystal structure when the microwave flow is applied along the low symmetry axis of ZrSe₃.The spin-orbit torque efficiency of the ZrSe₃（7.6 nm）/Py system is calculated to be 2.67,and the spin Hall conductivity is as high as 377.1×10³（（?）/2e）（Ωm）^-1.In order to further explore the source of the spin-orbit torque in ZrSe₃/Py system,we change the thickness of ZrSe₃.The analysis results show that the spin-orbit torque of the system mainly originates from the diffusion transport of the spin current brought about by bulk spin Hall effect.2.By inserting an ultrathin Cu layer into the ZrSe₃/Py interface,we found that the in-plane uniaxial magnetic anisotropy and the out-of-plane damping-like torque of the system both have obvious changes.The increase of Cu thickness suppresses the in-plane magnetic anisotropy of the Py layer induced by ZrSe₃.Additionally,the out-of-plane damping-like torque caused by symmetry breaking in ZrSe₃/Cu(t _Cu)/Py weakens with the increase of Cu thickness,and it is almost completely suppressed when Cu thickness is up to2 nm.Moreover,we find that the spin-orbit torque efficiency remains basically stable with the Cu thickness,further demonstrating the key role of the bulk spin Hall effect in ZrSe₃.3.The measurement results of changing the ferromagnetic thickness show that the magnetic damping factor of the ZrSe₃/Py(t _Py)system gradually decreases with the increase of the Py thickness.The results of external DC modulation show that the resonance linewidth and resonance field of the ZrSe₃/Py system both change with the magnitude of DC.By calculation,we obtain that the damping-like spin-orbit equivalent field H_DLof DC-induced is 0.120 Oe/m A,the field-like spin-orbit equivalent field H_FLis 0.193Oe/mA.