Structural Transition in the Hidden Ordered Phase of CeCoSi

TL;DR

This study reveals a structural transition to a triclinic phase in CeCoSi below 12 K, linked to a hidden electronic order that influences magnetic properties and is affected by external magnetic fields.

Contribution

The paper uncovers a triclinic lattice distortion in CeCoSi below the hidden order transition, demonstrating the interplay between structural, electronic, and magnetic phases.

Findings

Triclinic distortion occurs below 12 K in CeCoSi.

Structural domains can be manipulated by magnetic fields.

A hidden ordered phase exists between structural transition and magnetic ordering.

Abstract

We have performed X-ray diffraction experiments on a single crystalline CeCoSi to investigate the unresolved ordered phase below $T_0 \sim 12$ K. We have discovered that a triclinic lattice distortion takes place below $T_0$, which is further modified in the subsequent antiferromagnetic ordered phase. The structural domains can be selected by applying a magnetic field, indicating that some electronic ordering exists behind and affects the magnetic anisotropy in the hidden ordered phase below $T_0$. The transition at $T_0$, although the order parameter is still unknown, is associated with the maximum in the $c$-axis lattice parameter. In magnetic fields along $[1, 0, 0]$, the structural transition temperature, named as $T_{\text{s1}}$, deviates from $T_0$ and decreases with increasing the field, whereas $T_0$ increases. This shows that the hidden ordered phase without triclinic distortion exists between $T_{\text{s1}}$ and $T_0$. The results for $H \parallel [1, 1, 0]$ are also reported.