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

Abstract

The dc electrical resistivity $\ensuremath{\rho}$ 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 ${10}^{\ensuremath{-}2}$ \ensuremath{\Omega}cm and contained $n\ensuremath{\sim}{10}^{19}$ 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 $\ensuremath{\mu}$, 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 ${T}_{C}\ensuremath{\cong}19$ K. The data are consistent with the interpretation that this peak was due largely to a decrease in $\ensuremath{\mu}$. 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 $\ensuremath{\mu}$, but at high fields the changes in $\ensuremath{\mu}$ 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 $\ensuremath{\rho}$ 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 $\ensuremath{\rho}$ 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.