Landau theory for magnetic and structural transitions in CeCo$_{0.85}$Fe$_{0.15}$Si

TL;DR

This paper uses Landau theory to analyze the magnetoelastic properties of CeCo$_{0.85}$Fe$_{0.15}$Si near its Néel temperature, revealing a structural transition influenced by strong magnetoelastic coupling and magnetic field effects.

Contribution

It provides a phenomenological Landau model explaining the interplay of magnetic and structural transitions in CeCo$_{0.85}$Fe$_{0.15}$Si, highlighting the role of magnetoelastic coupling.

Findings

Structural transition occurs at $T_s  T_N$ and is affected by magnetic field.

Strong magnetoelastic coupling influences thermal expansion and magnetostriction.

The transition may be analogous to tetragonal-orthorhombic transitions in Fe-based pnictides.

Abstract

We present a phenomenological analysis of the magnetoelastic properties of CeCo$_{0.85}$Fe$_{0.15}$Si at temperatures close to the N\'eel transition temperature $T_N$. Using a Landau functional we provide a qualitative description of the thermal expansion, magnetostriction, magnetization and specific heat data. We show that the available experimental results [Journal of Physics: Condensed Matter 28 346003 (2016)] are consistent with the presence of a structural transition at $T_s\gtrsim T_N$ and a strong magnetoelastic coupling. The magnetoelastic coupling presents a Janus-faced effect: while the structural transition is shifted to higher temperatures as the magnetic field is increased, the resulting striction at low temperatures decreases. The strong magnetoelastic coupling and the proximity of the structural transition to the onset temperature for magnetic fluctuations, suggest that the transition could be an analogue of the tetragonal to orthorhombic observed in Fe-based pcnictides.