MAGNETORESISTANCE EXTREMUM AT THE FIRST-ORDER VERWEY TRANSITION IN MAGNETITE (FE3O4)

A large negative magnetoresistance (MR) sharply peaked at the first-or der Verwey transition temperature T-V = 119.79+/-0.02 K has been measu red in a synthetic single crystal of magnetite Fe-3(1-delta)O-4, delta =0.0006. At H = 7.7 T the MR extremum exhibited a peak value of -17% a nd a full width at half maximum of 0.53+/-0.08 K. At the lower and hig her ends of the measurement interval 114-126 K encompassing T-V, negat ive 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 respec t to the zero-field value Delta sigma(0), according to Delta sigma(H) = k(B)\MR\. At T-V, the associated discontinuous change of the average magnetic moment [mu] obtained from the MR data was of the order of De lta mu = 0.1% of [mu]. This is concordant with the corresponding value obtained in previous magnetization studies.