Scalar order: possible candidate for order parameters in skutterudites

TL;DR

This paper proposes that a scalar order parameter explains the ordered phases in skutterudites, accounting for their magnetic and symmetry properties, and offers a unified framework for understanding different compounds.

Contribution

It introduces the scalar order parameter as a candidate for describing ordered phases in skutterudites, explaining magnetic behaviors and phase transition characteristics.

Findings

Scalar order preserves cubic symmetry in ordered phases.

Universal anisotropy ratio for transition temperature and magnetization.

Explanation of magnetic differences between PrFe4P12 and PrRu4P12.

Abstract

Phenomenological Landau analysis shows that the properties of ordered phases in some skutterudites are consistently accounted for by a scalar order parameter which preserves the cubic symmetry, even in the ordered phase. A universal value is found for the anisotropy ratio of the transition temperature in a magnetic field, homogeneous magnetization, and induced staggered magnetization. The difference in magnetic behavior between PrFe$_4$P$_{12}$ and PrRu$_4$P$_{12}$ near their phase transitions is explained within a single framework. For the low-field phase of PrFe$_4$P$_{12}$, the scalar order with the $\Gamma_{1g}$ symmetry can explain (i) the absence of field induced dipoles perpendicular to the magnetic field, (ii) isotropic magnetic susceptibility in the ordered phase, (iii) the field angle dependence of the transition temperature, and (iv) the splitting pattern of the $^{31}$P nuclear magnetic resonance (NMR) spectra. It is proposed how the order parameter in SmRu$_4$P$_{12}$ is identified by NMR analysis of a single crystal.