Abstract:
We critically investigate the purported existence of a multiglass state in the quantum paraelectrics SrTiO 3 and KTaO 3 doped with magnetic 3 d transition metals. We observe that the transition metals have limited solubility in these hosts, and that traces of impurity magnetic oxides persist even in the most well-processed specimens. Our dielectric measurements indicate that the polar nanoregions formed as a consequence of doping appear to lack co-operativity, and the associated relaxation process exhibits a thermally activated Arrhenius form. At lower temperatures, the dielectric susceptibility could be fit using the Barrett's formalism, indicating that the quantum-paraelectric nature of the host lattices is unaltered by the doping of magnetic transition metal oxides. All these doped quantum paraelectrics exhibit a crossover from the high-temperature Curie-Weiss regime to one dominated by quantum fluctuations, as evidenced by a T 2 dependence of the temperature-dependent dielectric susceptibility. The temperature dependence of the magnetic susceptibility indicates that magnetic signatures observed in some of the specimens could be solely ascribed to the presence of impurity oxides corresponding to the magnetic dopants used. Hence, the doped quantum paraelectrics appear to remain intrinsically paramagnetic down to the lowest measured temperatures, ruling out the presence of a multiglass state.