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

Abstract

We critically investigate the purported existence of a multiglass state in the quantum paraelectrics SrTiO3 and KTaO3 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.

Effect of (Cu/Fe)O5 bipyramid size and separation on magnetic and dielectric properties of rare earth layered perovskite LaBaCuFeO5 and LuBaCuFeO5

“…The independent nature of peak of ZFC curve with respect to the magnetic field indicates the absence of spin glass behavior in This variation of the peak temperature in the imaginary part of the dielectric constant is analyzed by Arrhenius and VF law. In contrast to LaBaCuFeO 5 , a better fit to the peak temperature is obtained by Arrhenius law in this compound 58 . This law is mathematically expressed as τ= τ 0 exp (E a /k B T)…”

Low temperature magnetic and dielectric properties of LnBaCuFeO5 (Ln =Nd, Eu, Gd, Ho and Yb)

“…Hence, in this case T 0 <E a /k B , which is a signature of weak coupling among the electric dipoles [19]. Hence, it can be said that in EuBaCuFeO 5 there is a presence of glassy electric-dipole dynamics below 100 K. Above 200 K, the magnitude of both ε′ and ε′′ increases significantly.…”

О возможности введения примеси железа в узлы A в SrTiO-=SUB=-3-=/SUB=-

“…Результаты, полученные при анализе рентгеновских данных, спектров XANES и спектров EXAFS, дают серьезные основания полагать, что атомы Fe при высокой температуре отжига входят, по крайней мере частично, в узлы A. Для более надежной идентификации Fe в узле A необходимо проведение исследований образцов с более высокой долей атомов в узле A и анализ спектров EXAFS, полученных при более низкой температуре. По нашим данным, примесь Fe в SrTiO 3 проявляет сильную нецентральность в узле A (смещение ∼ 1 ¦ ), аналогичную ранее установленной для образцов титаната стронция, легированных Mn и Co. Это объясняет причину наблюдавшихся в работе [23] релаксаций диэлектрической проницаемости.…”

“…Наш интерес к образцам, легированным железом, обусловлен тем, что диэлектрические измерения на керамических образцах SrTiO 3 (Fe) с намеренно созданным дефицитом стронция [23] обнаружили такие же релаксационные явления, как и в образцах, легированных нецентральными примесями Mn и Co. Это могло указывать на появление нецентральных атомов железа.…”