Double spin-glass-like behavior and antiferromagnetic superexchange interaction between Fe³⁺ ions in α-Ga_2-xFe_xO₃ (0 ≤ x ≤ 0.4)

Single phase of Fe³⁺-doped α-Ga_2-xFe_xO₃ (α -GF_xO, x=0.1, 0.2, 0.3, 0.4) is synthesized by treating the β -Ga_2-xFe_xO₃ (β -GF_xO) precursors at high temperatures and high pressures. Rietveld refinements of the X-ray diffraction data show that the lattice constants increase monotonically with the increase of Fe³⁺ content. Calorimetric measurements show that the temperature of the phase transition from α -GF_xO to β -GF_xO increases, while the associated enthalpy change decreases upon increasing Fe³⁺ content. The optical energy gap deduced from the reflectance measurement is found to decrease monotonically with the increase in Fe³⁺ content. From the measurements of magnetic field-dependent magnetization and temperature-dependent inverse molar susceptibility, we find that the superexchange interaction between Fe³⁺ ions is antiferromagnetic. Remnant magnetization is observed in the Fe³⁺-doped α -GF_xO and is attributed to the spin glass in the magnetic sublattice. At high Fe³⁺ doping level (x=0.4), two evident peaks are observed in the image part of the AC susceptibility χ" _ac. The frequency dependence in intensity of these two peaks as well as two spin freezing temperatures observed in the DC magnetization measurements of α -GF_0.4O is suggested to be the behavior of two spin glasses.