图 1  基于苏格兰胶带的高度定向热解石墨的微机械剥离示意图^[21]

Fig. 1.  An illustrative procedure of the Scotch-tape based micro mechanical cleavage of highly oriented pyrolytic graphite^[21].

图 2  利用液相剥离方法制备MoTe₂/WTe₂示意图^[30]

Fig. 2.  Schematic diagram of liquid exfoliation method for preparing MoTe₂/WTe₂ nanosheets^[30].

图 3  (a)外加垂直于Cr₂Ge₂Te₆层平面的电场与引起的磁各向异性能量的依赖关系^[39]; (b)在面内和面外易轴条件下, 反铁磁和铁磁态之间的能量差异^[40]

Fig. 3.  (a) Dependence of the magnetic anisotropy energy on the externally applied electric field which is perpendicular to the CGT layer plane^[39]; (b) energy difference of the AFM and FM configurations with the in-plane and out-of-plane easy axes^[40].

图 4  (a)被制备成Hall bar形状的用于输运测量的CGT/Pt异质结构的光学图像^[41]; (b) 由电流产生的类阻尼力矩(ΔB_DL)和类场力矩(ΔB_FL)作用于磁化矢量m而产生的有效场方向^[41]; (c) 面内场B_x = ± 100 mT时, CGT (8.9 nm)/Ta (6 nm)样品中电流驱动磁矩翻转曲线^[41]

Fig. 4.  (a) Optical image of a CGT/Pt heterostructure patterned into a Hall bar geometry (4 μm ×11 μm) for transport measurements^[41]; (b) orientation of effective fields due to current-induced damping-like torque (∆B_DL) and field-like torque (∆B_FL) acting on the magnetization vector m^[41]; (c) spin-orbit-torque switching of the magnetization in a CGT(8.9 nm)/Ta(6 nm) sample in the presence of an in-plane field B_x = ± 100 mT^[41].

图 5  (a)具有不同CGT厚度的CGT/Pt(10 nm) 异质结在5 K条件下测量的反常霍尔电阻; (b)在CGT(10.5 nm)/Ta(6 nm)样品中观察到的反常霍尔电阻; (c)不同温度下CGT(10.5 nm)/Ta(6 nm)异质结磁化强度的光学MCD测试结果^[41]

Fig. 5.  (a) Anomalous Hall resistance observed in CGT/Pt(10 nm) heterostructures at 5 K, for different CGT thicknesses; (b) anomalous Hall resistance observed in a CGT(10.5 nm)/Ta(6 nm) sample; (c) optical MCD detection of magnetization in the same CGT(10.5 nm)/Ta(6 nm) sample at different temperatures^[41].

图 6  (a) FGT/Pt双层结构示意图, 其中Pt层(顶部)被溅射在剥离的FGT(底部)上. 绿色箭头表示在Pt层内的面内电流可产生沿z方向的自旋流, 底部(顶部)Pt表面积累的自旋由红色(蓝色)箭头表示, 自旋流会对FGT的磁矩施加力矩, 并在存在平面磁场的情况下将其翻转^[50]. (b)用于输运测量的Hall bar器件的光学图像^[50]

Fig. 6.  (a) Schematic view of the FGT/Pt bilayer structure, Pt layer (top) is sputtered on top of the exfoliated FGT (bottom). The green arrow represents the in-plane current flowing in the Pt layer, which generates a spin current flowing in the z direction, the accumulated spins at the bottom (top) Pt surface are indicated by the red (blue) arrows, the spin current exerts torques on the magnetization of FGT and can switch it in the presence of an in-plane magnetic field^[50]. (b) Optical image of the measured Hall bar device^[50]

图 7  FGT/Pt双层薄膜的磁性性质　(a)不同温度下, 霍尔电阻随磁场的变化曲线; (b) FGT/Pt器件的阿罗特图, 其临界温度为158 K; (c) 90 K下, 反常霍尔电阻随面内(IP)和面外(OOP)磁场的变化曲线^[50]

Fig. 7.  Magnetic properties of FGT/Pt bilayer: (a) Hall resistance as a function of magnetic field at different temperatures; (b) arrott plots of the Hall resistance of the FGT/Pt device, and the determined T_C is 158 K; (c) R_AHE as a function of in-plane (IP) and out-of-plane (OOP) magnetic field at 90 K^[50].

图 8  FGT/Pt双层膜器件中的自旋轨道力矩驱动的垂直磁矩翻转^[50]　(a), (b) 100 K温度下, 50 mT (a)和–50 mT (b)面内磁场辅助时实现的电流驱动的垂直磁矩翻转, 其翻转极性分别为逆时针和顺时针, 虚线对应饱和磁化状态下的R_AHE; (c) 10 K温度下, 300 mT面内辅助磁场下实现的电流驱动的垂直磁矩翻转(红色曲线), 箭头表示扫描电流方向; (d)不同温度下, 面内磁场和临界翻转电流的相图

Fig. 8.  SOT-driven perpendicular magnetization switching in the FGT/Pt bilayer device^[50]: (a), (b) Current-driven perpendicular magnetization switching for in-plane magnetic fields of 50 mT (a) and –50 mT (b) at 100 K, the switching polarity is anticlockwise and clockwise, respectively, the dashed lines correspond to the R_AHE at saturated magnetization states; (c) current-driven perpendicular magnetization switching with a 300 mT in-plane magnetic field at 10 K (red), the arrows indicate the current sweeping direction; (d) switching-phase diagram with respect to the in-plane magnetic fields and critical switching currents at different temperatures.

图 9  (a)基于二维Fe₃GeTe₂薄膜的Hall bar结构器件光学图像, 比例尺为10 μm^[51]; (b)经原子力显微镜测试, 样品厚度为21.3 nm^[51]; (c)纵向电阻R_xx随温度T的变化, 红色箭头表示由自旋翻转散射引起的磁性转变, 从中确定转变温度T_c = 185 K^[51]; (d) 2 K下, 霍尔电阻R_xy随磁场H的变化^[51]

Fig. 9.  (a) Optical image of a typical Fe₃GeTe₂ nanoflake sample with a Hall-bar geometry electrode, and the white scale bar represents 10 μm^[51]; (b) thickness of sample is 21.3 nm as measured by AFM^[51]; (c) longitudinal resistance R_xx as a function of temperature T with current = 0.05 mA, the red arrow indicates the magnetic transition due to spin-flip scattering, from which T_c = 185 K is determined^[51]; (d) Hall resistance R_xy as a function of magnetic field H at 2 K^[51].

图 10  (a) 2 K温度下, 当施加电流从0.05变化到1.5 mA时S1样品的霍尔曲线^[51]; (b) 2 K温度下, S1样品的矫顽场H_c和剩余霍尔电阻$ R_{xy}^{\text{r}} $随施加电流的变化曲线^[51]; (c) 2 K温度下, 样品S1 (21.3 nm), S2 (16.7 nm), S3 (6 nm), S4 (42 nm)和S5 (17.5 nm)的H_c(I )/H_c (其中I为最小电流)随施加电流的变化曲线^[51]; (d) 2 K温度下, 样品S1, S2, S3, S4和S5的H_c(j )/H_c (其中j ≈ l mA/m²)随电流密度j变化^[51]

Fig. 10.  (a) R_xy-H curves of sample S1 at 2 K with applied current varying I from 0.05 to 1.5 mA^[51]; (b) extracted coercive field H_c and remnant Hall resistance $ R_{xy}^{\text{r}} $ of sample Sl as a function of applied current I at 2 K^[51]; (c) H_c(I )/H_c (smallest I ) as a function of applied current for sample S1 (213 nm), S2 (167 nm), S3 (6 nm), S4 (42 nm), and S5 (17.5 nm) at 2 K^[51]; (d) H_c(j )/H_c (j ≈ l mA/m²) as a function of current density j for sample S1, S2, S3, S4, and S5 at 2 K^[51].