Slow dynamics and field-induced transitions in a mixed-valence oxide solid solution

In this study, the spin-glass-like properties of (x)FeTiO3-(1 - x)Fe2O3, with x = 0.8 and 0.9, as prominent mixed-valence state solid solution, were investigated by means of ac susceptibility and dc magnetization measurements. Dynamic ac susceptibility indicates freezing at finite temperature T-f, obeying a power law with a dynamic exponent z nu approximate to 7, close to that of the 3D Ising spin glass, and relaxation rates in the kHz range. The slow dynamics are explained by the presence of ordered superspins, whose relaxation rate decreases with increasing superspin size. In the frozen state, symmetry breaking is observed at a critical field H-cr which decreases with temperature obeying a power law H-cr(2/3) proportional to T, and is followed by a metamagnetic transition with increasing field similar to that of the end-member FeTiO3, obeying a H-cr(3/2)proportional to T law. The two transitions converge near the freezing temperature, thus denoting the H-T phase diagram of the system.