Mössbauer study of multiphase iron oxide composites

A representative nanocomposite made of ferrimagnetic γ-Fe2O3 and antiferromagnetic α-Fe2O3 nanoparticles with estimated weight fractions of ∼90 and ∼10%, respectively, and grown in transparent silica xerogels has been characterized by Mössbauer spectroscopy with respect to the temperature. The changes of the hyperfine parameters of the different subspectral components have been compared with other macroscopic magnetic and structural measurements. This comparison has allowed us to identify two different superparamagnetic transitions, located at ∼50 K and at ∼250 K, as well as the phases involved in each transition.