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.