Magnetic properties and charge transfer transition induced by Jahn-Teller effect in FeGa2O4 nanoparticles

Complex iron–gallium oxide nanoparticles FeGa2O4/FeGaO3 with a cubic spinel structure and the size of about 30 nm were synthesized by the combustion method. In the process of the synthesis, a new phase γ-FeGaO3 created at the surface of the FeGa2O4 core adopts the spinel structure of the core. In the pure FeGa2O4 compound, the cation distribution obtained from the Mossbauer data is (Fe2+0.76Ga3+0.24)tet [Fe2+0.24Ga3+1.76]oct O4 at room temperature. With decreasing temperature, the Jahn–Teller distortions of tetrahedral A-sites initiate the charge transfer transition at 140–90 K leading to the redistribution of Fe2+ and Ga3+ cations over the A- and B-sites. A fine correlation and connection between the critical temperature and critical concentration of the J-T ions associated with transition from the dynamic to cooperative J-T effect was observed. At low temperatures, the magnetic and Mossbauer measurements reveal a highly frustrated magnetic structure of spin-glass type with the spin-freezing temperature ...