In this study, the spin-glass-like properties of ($x$)FeTiO${}_3$–$(1-x$)Fe${}_2$O${}_3$, with $x$ $=0.8$ and 0.9, as prominent mixed-valence state solid solution, were investigated by means of $\mathit{ac}$ susceptibility and $\mathit{dc}$ magnetization measurements. Dynamic $\mathit{ac}$ susceptibility indicates freezing at finite temperature $T_{\mathrm{f}}$, obeying a power law with a dynamic exponent $z\nu \approx 7$, 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 $H_{\mathrm{cr}}$ which decreases with temperature obeying a power law $H_{\mathrm{cr}}^{2/3}\propto T$, and is followed by a metamagnetic transition with increasing field similar to that of the end-member FeTiO${}_3$, obeying a $H_{\mathrm{cr}}^{3/2}\propto T$ law. The two transitions converge near the freezing temperature, thus denoting the $H$–$T$ phase diagram of the system.

• Received 21 January 2011

DOI:https://doi.org/10.1103/PhysRevB.83.224414