Magnetoresistance extremum at the first-order Verwey transition in magnetite (${\mathrm{Fe}}_3$${\mathrm{O}}_4$)

A large negative magnetoresistance (MR) sharply peaked at the first-order Verwey transition temperature $T_V=119.79\mathrm{}\pm 0.02$ K has been measured in a synthetic single crystal of magnetite ${\mathrm{Fe}}_{3(1-\delta )}{\mathrm{O}}_4$, $\delta =0.0006\mathrm{}$. At $H=7.7\mathrm{}$ T the MR extremum exhibited a peak value of -17% and a full width at half maximum of 0.53±0.08 K. At the lower and higher ends of the measurement interval 114-126 K encompassing $T_V$, negative MR values of 3% and 0.5%, respectively, were obtained at 7.7 T. In applied magnetic fields up to 7.7 T the field-dependent discontinuous entropy change at $T_V$, $\Delta {\sigma }_H$, decreases linearly with respect to the zero-field value $\Delta {\sigma }_0$, according to $\Delta {\sigma }_H=\Delta {\sigma }_0-k_B\left|\mathrm{MR}\right|$. At $T_V$, the associated discontinuous change of the average magnetic moment $〈\mu 〉$ obtained from the MR data was of the order of $\Delta \mu =0.1\%$ of $〈\mu 〉$. This is concordant with the corresponding value obtained in previous magnetization studies.