Anomalous and Topological Hall Effects in Antiferromagnetic EuSn2As2 Nanostructures

Abstract

We investigate magnetotransport in exfoliated nanostructures of the candidate magnetic 3D topological insulator $\mathrm{EuSn_{2}As_{2}}$. Similar to macroscopic single crystals, the negative magnetoresistance observed below the Néel temperature ($T_N$ = 24 K) is related to the canted antiferromagnetic state (CAF) of an easy-plane antiferromagnet (AFM), with an increase of the saturation field when tilting the applied magnetic field away from the (ab) plane ($μ_{0} H^{c}_{s}$ = 4.9 T, $μ_{0} H^{ab}_{s}$ = 3.6 T). Higher-accuracy measurements in nanostructures up to 14 T further evidence a non-linear normal Hall response due to several electronic bands. Interestingly, the transverse resistance due to magnetism reveals an anomalous Hall effect in the CAF state, but also a topological Hall effect due to chiral spin textures, as found in AFM or helical magnets. The presence of real-space chiral spin texture, already reported in another magnetic topological insulator, $\mathrm{MnBi_{2}Te_{4}}$, could be a characteristic generally appearing in magnetic 3D topological insulators.

Figures (10)

• Figure 1: (\ref{['subfig:crystal_structure']}) Crystal structure of EuSn2As2; (\ref{['subfig:nanostructures']}) studied nanostructures: 140; 110; 60 (from top to bottom); (\ref{['subfig:R_vs_T']}) temperature dependence of longitudinal resistance $R_{xx}$ of 110 sample at zero magnetic field and 14 (inset).
• Figure 2: Magnetoresistance of EuSn2As2 110 flake (\ref{['subfig:MR_OOP_110nm']}) for different temperatures in an out-of-plane orientation (symmetrized data to account for contacts misalignment, vertical shift of 2 % is added for clarity), (\ref{['subfig:MR_tilts_110nm']}) for different field orientations at 2 (data without symmetrizaion, vertical shift of 1 % is added for clarity). (\ref{['subfig:Rxx_polar_110nm']}) Polar diagram of $R_{xx}$ for different applied magnetic field strength. 0 is out-of-plane, 90 is in-plane.
• Figure 3: Hall measurements on the 110 flake. (\ref{['subfig:Hall_110nm']}) Antisymmetrized Hall effect measured at different temperatures. (\ref{['subfig:AHElin_110nm']}) Residuals of the Hall effect in a after subtracting a high-field (11-13T) linear slope. Magnetization curves measured on a single crystal (scatter points -- measured, solid lines -- interpolation) are shown for reference. Below saturation fields an anomaly is clearly visible for $T < T_N$. (\ref{['subfig:AHE_110nm']}) Residual Hall response after suppression of the normal Hall contributions calculated as $\rho_{xy}(T) - \rho_{xy}(\mathrm{30K})$, showing two contributions to the Hall effect from magnetism. (\ref{['subfig:THE_110nm']}) Topological Hall effect: residuals of Hall effect curves after subtraction of $\rho_{xy}(\mathrm{30K})$ and of the scaled magnetization data ($\rho_{xy}(T) - \rho_{xy}(\mathrm{30K}) - \alpha \Delta M(T)$, see main text).
• Figure S1: Step-by-step procedure of Hall effect analysis for 110nm flake data at 4. (\ref{['subfig:rhoxx_fit']}, \ref{['subfig:rhoxy_fit']}) Longitudinal $\rho_{xx}$ and transversal $\rho_{xy}$ resistivities along with fit results (dashed line on (\ref{['subfig:rhoxy_fit']}) denotes line $kB$). Thickened portions of the curves indicate the data intervals used for fitting. (\ref{['subfig:drhoxy_linfit']}) Residuals $\Delta\rho^{lin}_{xy} = \rho_{xy} - kB$. (\ref{['subfig:drhoxy_30K']}) Residuals showing magnetic contributions to Hall effect calculated as $\rho^{30K}_{xy} = \rho_{xy}(T)-\rho_{xy}(30\mathrm{K})$ and scaled magnetization $\alpha \Delta M$ ($\Delta M = M(\mathrm{4K})-M(\mathrm{30K})$). (\ref{['subfig:rhoxy_the']}) topological Hall effect $\Delta\rho^{THE}_{xy} = \Delta\rho^{30K}_{xy} - \alpha \Delta M$.
• Figure S2: Temperature dependence of free parameters $n_{h}$, $\mu_{h}$, $n_{e}$, $\mu_{e}$ found from two-band fits for 140; 110; 60 flakes.