Narrow-gap semiconducting behavior in antiferromagnetic ${\mathrm{Eu}}_{11}{\mathrm{InSb}}_9$

Here we investigate the thermodynamic and electronic properties of ${\mathrm{Eu}}_{11}\mathrm{In}{\mathrm{Sb}}_9$ single crystals. Electrical transport data show that ${\mathrm{Eu}}_{11}\mathrm{In}{\mathrm{Sb}}_9$ has a semiconducting ground state with a relatively narrow band gap of 320 meV. Magnetic susceptibility data reveal antiferromagnetic order at low temperatures, whereas ferromagnetic interactions dominate at high temperature. Specific heat, magnetic susceptibility, and electrical resistivity measurements reveal three phase transitions at $T_{N1}=9.3$ K, $T_{N2}=8.3$ K, and $T_{N3}=4.3$ K. Unlike ${\mathrm{Eu}}_5{\mathrm{In}}_2{\mathrm{Sb}}_6$, a related europium-containing Zintl compound, no colossal magnetoresistance (CMR) is observed in ${\mathrm{Eu}}_{11}\mathrm{In}{\mathrm{Sb}}_9$. We attribute the absence of CMR to the smaller carrier density and the larger distance between Eu ions and In-Sb polyhedra in ${\mathrm{Eu}}_{11}\mathrm{In}{\mathrm{Sb}}_9$. Our results indicate that ${\mathrm{Eu}}_{11}\mathrm{In}{\mathrm{Sb}}_9$ has potential applications as a thermoelectric material through doping or as a long-wavelength detector due to its narrow gap.

Figure 1

(a) Specific heat divided by temperature $T, C/T$ vs $T$, at zero magnetic field of ${\mathrm{Eu}}_{11}\mathrm{In}{\mathrm{Sb}}_9$. The inset displays the entropy in units of $R\ln 8$. (b) Temperature dependent magnetic susceptibility $\chi \left(T\right)$ with a field of 1 kOe applied along distinct crystallographic directions. The inset shows the low-temperature anisotropic $\chi \left(T\right)$ data. (c) Inverse magnetic susceptibility 1/$\chi \left(T\right)$ vs $T$. A Curie-Weiss fit is shown by a solid line. The inset shows $\chi T$ as a function of temperature.

Figure 2

(a) Low temperature susceptibility in the $a$ axis. (b) Low temperature susceptibility in the $b$ axis. (c) Low temperature susceptibility in the $c$ axis. (d) Zero-field and field-cooled magnetization curves. (e) Low temperature anisotropic magnetization, zero-field cooled, with the inset showing the low-temperature region with hysteresis for $H\left|\right|b$ around $H=0$. (f) Derivative with respect to field taken from (e) shows field induced transitions in the a,b, and $c$ axis.

Figure 3

(a) Electrical resistivity, $\rho$, versus temperature of ${\mathrm{Eu}}_{11}\mathrm{In}{\mathrm{Sb}}_9$ (sample 1). Inset shows $\log \left(\rho \right) vs T$. (b) Low-temperature electrical resistivity measurements for sample 2. Inset maps transitions identified in both magnetic and specific heat measurements. (c) Hall resistivity ${\rho }_H \mathit{vs}$ magnetic field of sample 1 measured with field along the $c$ axis. The black line is a linear fit to the data, which agrees with antisymmetrized data and suggests no measurable contribution from longitudinal resistance. (d) Normalized magnetoresistance $(\mathrm{MR}=\left(\rho \left(T\right)\text{−}{\rho }_0\right)/{\rho }_0)$ as percent for sample 1.

Figure 4

Arrhenius plot ($\ln \left(\rho \right) vs.$ 1/$T$) for ${\mathrm{Eu}}_{11}\mathrm{In}{\mathrm{Sb}}_9$. Resistivity data are from Fig. 3.