Phenomenological theory of a scalar electronic order: application to skutterudite PrFe4P12

TL;DR

This paper develops a phenomenological Landau theory with a scalar order parameter to explain the phase transition and related properties in PrFe4P12, including magnetic and elastic anomalies, under various conditions.

Contribution

It introduces a scalar-order model with specific symmetry to unify the understanding of magnetic and elastic anomalies in PrFe4P12.

Findings

Reproduces magnetic susceptibility anomaly at transition

Explains elastic constant anomaly in magnetic field

Describes anisotropy under uniaxial pressure

Abstract

By phenomenological Landau analysis, it is shown that a scalar order parameter with the point-group symmetry $\Gamma_{1g}$ explains most properties associated with the phase transition in PrFe$_4$P$_{12}$ at 6.5 K. The scalar-order model reproduces magnetic and elastic properties in PrFe$_4$P$_{12}$ consistently such as (i) the anomaly of the magnetic susceptibility and elastic constant at the transition temperature, (ii) anisotropy of the magnetic susceptibility in the presence of uniaxial pressure, and (iii) the anomaly in the elastic constant in magnetic field. An Ehrenfest relation is derived which relates the anomaly of the magnetic susceptibility to that of the elastic constant at the transition.