  Evidence for a re-entrant quantum paraelectric (QPE) state preceded by a
dipole glass (DG) phase with a non-classical exponent in the quantum critical
regime of SrFe12O19 is presented. It is shown that the DG transition is
accompanied with a spin glass (SG) transition and presence of a biquadratic
coupling of two diverse order parameter fields. Further, the ergodic symmetry
breaking temperatures for the DG and SG transitions coincide (TDG ~ TSG) within
+/- 1K suggesting that SrFe12O19 exhibits a canonical multiglass state. The
stability of the dipole glass state is enhanced magnetically as evidenced by
the increase in the freezing temperature with magnetic field (H). The
re-entrant 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, at a constant 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 higher magnetic fields 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 a multiglass system.
