Raman Study of the Verwey Transition in Magnetite (Fe$_{3}$O$_{4})$ at High Pressure and Low Temperature: Effect of Aluminum Doping

Raman spectra of pure and doped magnetite provide a set of markers allowing one to study how the Verwey transition in magnetite changes with the change of pressure. At ambient pressure Verwey transition temperature, T$_{v}$, of the single crystals of magnetite, Fe$_{3}$O$_{4}$, is determined to be 123K. High-pressure experiment indicates strong dependence of the change of pressure vs. change in the Verwey transition temperature$_{ }$on the amount of impurities: for pure Fe$_{3}$O$_{4}$ the change is -0.2 GPa/K; for doped iron, Fe$_{2.98}$Al$_{0.02}$O$_{4}$, the change is -0.09 GPa/K. Aluminum-doped magnetite (Fe$_{2.98}$Al$_{0.02}$O$_{4})$ where Al substitutes Fe$^{+2}$ and Fe$^{+3}$ atoms, represents a 2{\%} aluminum doping, which shifts the Verwey transition temperature to T$_{v}$=118.5K. The rate with which the Verwey temperature decreases with pressure is further discussed based on the molar specific heat measurements.