Size-Dependent Thermodynamics of Structural Transition and Magnetic Properties of Nano-Fe2O3

Fe2O3 is widely used in the field of magnetism, and its magnetic properties are affected by particle size and crystalline form. Therefore, it is of great importance to study the effects of particle size on the structural transitions and magnetic properties. In this paper, accurate relations were derived to describe size dependence of the integral enthalpy and entropy of structural transitions of nanocrystals, and the influence mechanism of particle size on the thermodynamic properties of structural transitions is discussed. Different sizes of nano-Fe2O3 were prepared, and differential scanning calorimetry (DSC) was used to obtain the temperature, enthalpy, and entropy of the structural transition from maghemite (γ-Fe2O3) to hematite (α-Fe2O3). The magnetic properties of nano-γ-Fe2O3 were determined on the Magnetic Property Measurement System. We found that the thermodynamic properties of the structural transition decrease as particle size decreases and vary linearly with the reciprocal of particle size wi...