Large anomalous Hall and Nernst effects in the ferromagnetic semimetal candidate ${\mathrm{Mn}}_3{\mathrm{Sn}}_2$

Recent theoretical calculations have shown that ${\mathrm{Mn}}_3{\mathrm{Sn}}_2$, a well-known magnetocaloric material with multiple magnetic transitions, possesses both nodal lines and nodal surfaces in its electronic structures, making it an excellent platform for studying anomalous transport properties in magnetic topological candidates. In this work, we performed comprehensive electrical, thermal, and thermoelectric measurements on ${\mathrm{Mn}}_3{\mathrm{Sn}}_2$ single crystals. The electrical resistivity $\rho \left(T\right)$ shows an abnormal peak near the Curie temperature, $T_{\mathrm{C}2}\sim 227$ K, and a negative resistivity slope above $T_{\mathrm{C}2}$, which are probably related to a large spin-fluctuation scattering. The Seebeck coefficient $S_{xx}\left(T\right)$ shows a sign reversal below 80 K although the Hall coefficient is always positive, which might be ascribed to the magnon-drag effect. Below $T_{\mathrm{C}1}\sim 262$ K, a significant anomalous Hall effect is observed, and the anomalous Hall resistance $\left({\rho }_{\mathrm{xy}}^A\right)$ peaks at around 7 µΩ cm at 200 K. ${\rho }_{\mathrm{xy}}^A$ exhibits a quadratic dependence on the longitudinal resistivity ${\rho }_{xx}$, and the anomalous Hall conductivity ${\sigma }_{\mathrm{xy}}^A$ remains nearly temperature independent below 200 K, suggesting the dominance of the intrinsic Berry-phase mechanism. Correspondingly, we also detect a large anomalous Nernst effect, with the anomalous Nernst coefficient reaching approximately $1\mu \mathrm{V}{\mathrm{K}}^{-1}$ at 200 K. Despite ${\mathrm{Mn}}_3{\mathrm{Sn}}_2$ exhibiting robust ferromagnetism, its anomalous Hall angle (2.5%), anomalous Nernst angle (6.5%), and large anomalous Nernst coefficient $\left(1.65\mu \mathrm{V}{\mathrm{K}}^{-1}{\mathrm{T}}^{-1}\right)$ surpass those observed in typical ferromagnetic materials. Our results experimentally demonstrate the existence of topologically nontrivial states in ${\mathrm{Mn}}_3{\mathrm{Sn}}_2$.

Figure 1

(a) Temperature-dependent magnetization of ${\mathrm{Mn}}_3{\mathrm{Sn}}_2$ measured in the zero-field-cooling mode at ${\mu }_{0}H=0.01$ T, with H parallel to $b$ and $c$ axis, respectively. The dotted lines indicate the positions of the magnetic phase transitions. The inset shows the optical image of a single crystal sample with respect to the crystalline axes on a millimeter grid. (b) Magnetic field dependent magnetization measured with H // $c$ under various temperatures. (c) Temperature dependence of ${\rho }_{xx}$ without a magnetic field. The vertical lines show the positions of the two ferromagnetic transitions. The right inset presents the results of fitting the low temperature resistance with equation ${\rho }_{xx}\left(T\right)={\rho }_0+a{T}^m$. The left inset shows the contact configuration for measuring the electrical transport properties. A small kink is observed at $T_{\mathrm{C}1}\sim 262$ K where the resistivity increases faster and the maximum appears at $T_{\mathrm{C}2}\sim 227$ K, corresponding to the two ferromagnetic transitions while no anomaly is visible at $T_{\mathrm{N}}$. (d) The magnetic field dependent magnetoresistance measured under selected temperatures with H parallel to $c$ axis and the current I parallel to $b$ axis.

Figure 2

(a) Magnetic field dependence of the Hall resistivity measured at selected temperatures with H parallel to $c$ axis and the current I parallel to $b$ axis. The inset shows the temperature dependence of both ordinary and anomalous Hall coefficients. (b) Magnetic field dependence of Hall conductivity ${\sigma }_{xx}$. The inset presents the extracted carrier density $n_h$ and mobility ${\mu }_h$ using a one-band model. (c) Plot of M and $-{\sigma }_{xy}^A$ versus ${\sigma }_{xx}$, here the temperature is an implicit parameter. The inset shows the plot of $-{\rho }_{xy}^A/M{\rho }_{xx}$ versus ${\rho }_{xx}$ with the blue line indicating a linear fit to Eq. (7). (d) ${\theta }_{\mathrm{AH}}$ vs ${\sigma }_{xx}$ plot for ${\mathrm{Mn}}_3{\mathrm{Sn}}_2$ and other reported anomalous Hall materials. Except for ${\mathrm{Mn}}_3{\mathrm{Sn}}_2$, the data for other materials were extracted from Refs. [18, 29, 30, 31, 32, 33, 34].

Figure 3

(a) Temperature dependence of total thermal conductivity κ, electronic thermal conductivity ${\kappa }_e$, and lattice thermal conductivity $\kappa -{\kappa }_e$. (b) Plot of Seebeck coefficient $S_{xx}$ versus T measured without an external field. The vertical dotted lines indicate the positions of the two ferromagnetic phase transitions and the red arrow marks the zero point of $S_{xx}$. (c) Magnetic field dependence of Nernst effect at selected temperatures. The inset shows the temperature dependence of anomalous Nernst effect and the corresponding $S_{xx}$. (d) The temperature dependence of the anomalous Nernst coefficient. The inset shows the contact configuration for measuring the thermal transport properties, i.e., the temperature gradient $\mathrm{\Delta }T$ is parallel to $b$ axis and H is parallel to $c$ axis.

Figure 4

(a) ${\theta }_{\mathrm{AN}}$ vs $|S_{xy}^A|$ plot for ${\mathrm{Mn}}_3{\mathrm{Sn}}_2$ (at 200 K) and other reported anomalous Nernst materials. (b) Full logarithmic plot of the anomalous Nernst signal $|S_{xy}^A|$ versus the magnetization ${\mu }_{0}M$ for a variety of metals and ${\mathrm{Mn}}_3{\mathrm{Sn}}_2$ (at 200 K). The shaded region indicates the linear relation for conventional ferromagnetic metals with $|N_{xy}^A|$ ranging $0.05-1\mu \mathrm{V}{\mathrm{K}}^{-1}{\mathrm{T}}^{-1}$. Except for ${\mathrm{Mn}}_3{\mathrm{Sn}}_2$, the other data were taken from Refs. [7, 8, 19, 31, 45, 46, 47].