Quantum Critical Point study in Multiferroic Hexaferrites: BaFe12O19, SrFe12O19, and PbFe3Ga9O19 -- Verification of the Khmelnitskii Theory

TL;DR

This study verifies Khmelnitskii's quantum critical point theory by examining the temperature dependence of electric susceptibility in specific multiferroic hexaferrites, revealing distinct behavior from cubic ferroelectrics.

Contribution

It provides experimental validation of the T^3 susceptibility variation predicted by Khmelnitskii's theory in uniaxial ferroelectrics.

Findings

Inverse isothermal electric susceptibility varies as T^3 in the studied hexaferrites.

Verification of the Khmelnitskii theory for uniaxial ferroelectrics.

Contrasts with behavior in pseudo-cubic ferroelectrics.

Abstract

BaFe12O19 is a popular M-type hexaferrite with T(Neel) = 720 K of enormous commercial value (3 billion dollars/year). It exhibits an incipient ferroelectric phase transition (in violation of the Spaldin-Hill rule) extrapolated to lie at 6.0 K Kelvin but suppressed due to quantum fluctuations (as in SrTiO3). The QCP theory of Khmelnitskii for such uniaxial ferroelectrics predicts that the inverse isothermal electric susceptibility varies as T cubed, in contrast to that for pseudo-cubic materials such as SrTiO3 or KTaO3, a hypothesis we verify.