Resistivity and Hall Effect of EuS in Fields up to 140 kOe

The dc electrical resistivity $\rho$ and Hall effect were measured in $n$-type EuS single crystals. Data were taken from 300 to 2 K in magnetic fields $H$ up to 140 kOe. At room temperature all samples had resistivities of the order ${10}^{-2\mathrm{}}$ Ωcm and contained $n\sim {10}^{19}$ conduction electrons/${\mathrm{cm}}^3$. Negative magnetoresistance was observed at all temperatures. At 77 K the negative magnetoresistance was due mostly to an increase in the mobility $\mu$, although a small increase in $n$ with increasing $H$ was also observed. The zero-field resistivity as a function of temperature $T$ exhibited a very large peak near the Curie temperature $T_C\cong 19$ K. The data are consistent with the interpretation that this peak was due largely to a decrease in $\mu$. In the presence of a magnetic field the resistivity peak decreased in magnitude, became broader, and shifted to a higher temperature. A very large negative magnetoresistance was observed near $T_C$. At moderate fields this negative magnetoresistance was due largely to an increase in $\mu$, but at high fields the changes in $\mu$ and $n$ were comparable. Well below $T_C$, the resistivity and Hall coefficient exhibited hysteresis as a function of $H$, and were constant at fields above magnetic saturation. In the field-increasing part of the hysteresis cycle $\rho$ decreased monotonically with time. A resistivity "elbow," similar to the one observed earlier in Eu-rich EuO, was observed also in the Eu-rich EuS samples. With increasing $H$ the elbow shifted to higher temperatures. Hall-effect measurements at 4.2 K indicated that at fields above magnetic saturation the anomalous Hall term was small compared to the normal term. The Hall data also showed that a large part of both the hysteresis in $\rho$ and the resistivity elbow were due to a change in $n$. The various data are compared with theoretical models and earlier electrical-transport measurements on the Eu chalcogenides.