Thermodynamic Properties of α-Fe2O3 and Fe3O4 Nanoparticles

The thermodynamic properties of hydrated α-Fe2O3 (hematite) and Fe3O4 (magnetite) nanoparticles have been comprehensively assessed. In addition to 9 nm Fe3O4, three α-Fe2O3 nanoparticles samples of different sizes (11, 14, and 25 nm) and bulk α-Fe2O3 have been evaluated by inelastic neutron scattering methods. The contribution of the two-level magnetic spin flip transition to the heat capacity of the α-Fe2O3 particles has been determined. The isochoric heat capacity of the water confined on the surface of these two types of iron oxide particles have been calculated from their INS spectra, and is affected by the chemical composition of the underlying particle. Furthermore, the heat capacity and dynamics of the particle hydration layers appear to be influenced by a complex array of factors including particle size, water coverage, and possibly the magnetic state of the particle itself.