Stability of the first-order character of phase transition in HoCo$_2$

TL;DR

This study investigates the thermodynamic nature of the phase transition in HoCo$_2$, revealing that its first-order character remains stable under magnetic fields up to 7 T, which is important for magnetocaloric applications.

Contribution

The paper provides a comprehensive analysis showing the stability of the first-order phase transition in HoCo$_2$ under high magnetic fields, challenging previous assumptions of transition transformation.

Findings

First-order transition remains stable up to 7 T.

Transformation from first- to second-order behavior is only qualitative.

Modified Arrott plots show negative slope indicating first-order stability.

Abstract

HoCo$_2$ exhibits a giant magnetocaloric (MC) effect at its first-order magnetostructural phase transition around 77~K, and understanding the thermodynamic nature of this transition in response to external magnetic fields is crucial for its MC applications. In this study, we present a comprehensive investigation of specific heat and magnetization measurements of HoCo$_2$ under varying magnetic fields. The specific heat measurements qualitatively indicate a transformation from first- to second-order behavior of this phase transition at higher magnetic fields. However, analysis of the power-law dependence of the magnetic entropy change ($\Delta S_{\rm M} \propto$ H$^n$) and the breakdown of universal behavior in the temperature dependence of $\Delta S_{\rm M}$ suggest that the first-order nature remains intact, even up to 7 T. This stability of the first-order nature is further manifested through the distinctive non-linear behavior of modified Arrott plots, with a negative slope in the 6--7 T range.