Studies of the Verwey Transition in Magnetite

Abstract

Studies of the specific heat and simultaneous AC magnetic susceptibility (χ ) and electric resistance of stoichiometric magnetite single crystal are presented. The temperature hysteresis of the Verwey transition is of 0.03 K found from the specific heat data confirming its first-order character. The continuous temporal change of χ at T V can be switched off by an external magnetic field without affecting the transition. The electrical resistance decreases continuously with increasing temperature with a rapid change of slope at the point when the phase transition is completed. It was concluded that the magnetic degrees of freedom do not actively participate in the transition and that the entropy released at TV may come from ordering electrons.

Magnetic and structural studies of magnetite at the Verwey transition

“…In other words, we wanted to trace the transition during the process and to simultaneously measure the temporal dependence of as many physical characteristics as possible. The simultaneous measurements of the electrical resistance R, magnetic susceptibility χ as well as the temporal temperature profile T(t) for stoichiometric magnetite have already been presented [6]. Here we provide results for magnetite samples low doped with zinc, exhibiting the Verwey transition of first and second order and we show some preliminary results on the structural changes during the Verwey transition in stoichiometric magnetite.…”

“…To measure the temperature hysteresis of the transition, very precise heat capacity studies were performed on the stoichiometric sample [6]; we are certain that the hysteresis of the Verwey transition exist and it does not exceed 0.03 K. Several artifact reports in the literature claiming larger hysteresis for stoichiometric magnetite may easily be caused by not properly taking into account the huge heat capacity at the transition (and the large anomaly in heat conduction [8]): the thermometer reflects the probe properties of the heater rather than the sample temperature. To estimate the hysteresis in zinc doped magnetite, where the heat capacity is much lower and the anomaly in heat transfer is not so pronounced, the samples were heated with the current passing through them (as opposed to heating with the probe heater that could bring about erroneous temperature reading) in several stages of the transition.…”

Influence of thermal treatments on phase formation and magnetic behaviour in metal transition doped TiO2

“…In the Fe doped samples a jump in the magnitude of the in-phase susceptibility was detected at approximately 120 K. This jump was associated to the Verwey transition [4] of magnetite (Fe 3 O 4 ): the absence of evidence for this phase in XRD and MS results may be due to its very small relative abundance, which difficults its detection, especially by MS since their hyperfine parameters are close to those of hematite.…”

AC magnetic susceptibility under pressure and Mössbauer effect studies of the isotropy point TIP in magnetite

“…On the other hand, some ordering certainly develops below T V , what can easily be observed by, e.g. AC magnetic susceptibility studies [7] at T V , or by the axis switching [8] at temperatures below T V , the phenomenon strictly related to the transition.…”