Absence of a multiglass state in some transition metal doped quantum paraelectrics

TL;DR

This study investigates whether doping quantum paraelectrics SrTiO3 and KTaO3 with magnetic transition metals induces a multiglass state, finding no evidence for such a state and attributing magnetic signals to impurities.

Contribution

The paper provides a detailed analysis showing that magnetic doping does not produce a multiglass state in these quantum paraelectrics, clarifying previous ambiguities.

Findings

Impurity magnetic oxides are present despite processing.

Doping does not alter the quantum paraelectric nature.

Magnetic signatures are due to impurities, not intrinsic magnetism.

Abstract

We critically investigate the purported existence of a multiglass state in the quantum paraelectrics SrTiO${_3}$ and KTaO${_3}$ doped with magnetic 3d 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 nano-regions 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 are 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 indicate 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.