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Evidence is presented for a reentrant quantum paraelectric (QPE) state preceded by a dipole glass (DG) phase with a nonclassical exponent in the quantum critical regime of SrFe₁₂O₁₉. It is shown that the DG transition is accompanied by a spin glass (SG) transition. Further, the ergodic symmetry-breaking temperatures for the DG and SG transitions coincide (T₃₆Tₒ₆) within 1 K suggesting that SrFe₁₂O₁₉ exhibits a canonical multiglass state. It is shown that these transitions are coupled through biquadratic and lower order couplings of two diverse order parameter fields. The stability of the dipole glass state is enhanced magnetically as evidenced by the increase in the freezing temperature with magnetic field (H). The reentrant QPE state, on the other hand, is found to give way to another frequency-dependent peak in the temperature dependence of dielectric constant, most likely a DG phase, under dc magnetic field (H). Further, this transition is not linked to any magnetic transition, in sharp contrast to the higher temperature multiglass transition. The transition temperature of this phase decreases with increasing magnetic field for a fixed frequency unlike the higher temperature DG transition. This raises the possibility of locating a quantum critical point (QCP) in this system at a higher magnetic field than that used in the present work. These results are discussed in the light of quantum critical models of multiferroic transitions. Our results highlight the need for more theoretical studies specific to multiferroic quantum criticality in multiglass systems.
Kumar et al. (Wed,) studied this question.