Raman study of the Verwey transition in magnetite at high-pressure and low-temperature: Effect of Al doping

We employed Raman spectroscopy to investigate how the hydrostatic pressure affects the temperature of the Verwey transition in pure (Fe3O4) and Al-doped (Fe2.8Al0.2O4) magnetite. In both samples, pressure suppresses the transition. The Al-doped sample displays no transition above 8 GPa. We do not observe such discontinuity in a pure magnetite, which suggests that the discontinuity is doping driven. Our Clausius-Clapeyron formula based analysis of the pressure-transition temperature dependence is in excellent agreement with our data in pure magnetite. The Al doping leads to a smaller entropy change and larger volume expansion consistent with partial charge ordering at the transition. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4747834]