The magnetic transition in ε-Fe2O3 nanoparticles: Magnetic properties and hyperfine interactions from Mössbauer spectroscopy

The ⁵⁷Fe isotope enriched ε-Fe₂O₃ nanoparticles with characteristic size 25 nm, embedded in amorphous silica matrix, were prepared by sol-gel technique. From XRD, α-Fe₂O₃ and β-Fe₂O₃ were observed as minor iron oxide phases. The rather high coercivity of ∼2.1 T at room temperature was confirmed and a two-step magnetic transition spread between 100-153 K was indicated by magnetic measurements. The dependence of hyperfine parameters, obtained by Mössbauer spectroscopy, on temperature and external magnetic field suggests that the first step between 153–130 K is related to the spin reorientation of the local magnetic moments in the magnetic sublattices and the second step between 130-100 K may be associated with the intermediate spin–high spin state transition of Fe³⁺ cation in the tetrahedral sublattice.