Magnetostriction Reveals Orthorhombic Distortion in Tetrahedral Gd-compounds

TL;DR

This study uses magnetostriction and thermal expansion measurements, combined with a first-principles model, to reveal hidden orthorhombic distortions in Gd-compounds that break tetragonal symmetry but are not directly observable.

Contribution

The paper introduces a comprehensive model explaining magnetostriction and magnetic behavior, revealing orthorhombic distortions in Gd-compounds that are not detected by high-resolution x-ray experiments.

Findings

Metastable state transition at field B*

Coexistence of two degenerate phases below TN

Orthorhombic distortion is hidden in high-resolution x-ray data

Abstract

We report detailed thermal expansion and magnetostriction experiments on GdCoIn$_5$ and GdRhIn$_5$ single crystal samples that show a sudden change in the dilation at a field B$^\ast$ for temperatures below the N\'eel transition temperature TN. We present a first-principles model including crystal-field effects, dipolar and exchange interactions, and the dependence of the exchange couplings with lattice distortions in order to fully account for the magnetostriction and magnetic susceptibility data. The mean-field solution of the model shows that a transition between metastable states occurs at the field B$^\ast$. It also indicates that two degenerate phases coexist in the sample at temperatures below TN. This allows to explain the lack of observation, in high resolution x-ray experiments, of an orthorhombic distortion at the N\'eeel transition even though the magnetic structure breaks the tetragonal symmetry and the magnetoelastic coupling is significant. These conclusions could be extended to other tetragonal Gd-based compounds that present the same phenomenology.