Noncrystalline ferromagnetic iron-gallium oxide

Conductivity, magnetization, and Mössbauer spectra have been measured for a thin film of composition Fe0.503+Fe0.192+Ga1.37O3, sputtered from a target of FeGaO3. The film shows thermally activated electrical conductivity in the range 150-300 K with activation energy 0.26 (2) eV, and a room temperature resistivity of 3×104 Ω-cm. Signs of electronic relaxation typical of inhomogeneous mixed-valence materials appear in the Mössbauer spectra, but the activation energy there is smaller. The oxide orders ferromagnetically around 155(10) K. At 4.2 K, hysteresis is observed with a coercivity of 4.7 kOe, and a reduced remanence of 0.46. The ferromagnetism of the amorphous oxide is attributed to ferromagnetic interactions associated with Fe2+↔Fe3+ electron transfer, which are stronger than the usual Fe3+-O-Fe3+ antiferromagnetic superexchange.