Thermodynamics around the First-Order Ferromagnetic Phase Transition of ${\rm Fe}_2{\rm P}$ Single Crystals

TL;DR

This study empirically investigates the thermodynamics and phase diagram of Fe₂P single crystals around its first-order ferromagnetic transition, revealing how magnetic field orientation influences phase stability and transition characteristics.

Contribution

It provides detailed experimental insights into the magnetic field dependence of the phase transition in Fe₂P, highlighting anisotropic effects and phase stability limits.

Findings

Magnetic field orientation critically affects phase stability.

Distinct phase contours for parallel and perpendicular fields.

First-order transition shows different stability limits on heating and cooling.

Abstract

The specific heat and thermodynamics of ${\rm Fe}_2{\rm P}$ single-crystals around the first order paramagnetic (PM) to ferromagnetic (FM) phase transition at $T_{\rm C} = 217 \,{\rm K}$ are empirically investigated. The magnitude and direction of the magnetic field relative to the crystal axes govern the derived H-T phase diagram. Strikingly different phase contours are obtained for fields applied parallel and perpendicular to the $c$-axis of the crystal. In parallel fields, the FM state is stabilized, while in perpendicular fields, the phase transition is split into two, with an intermediate FM phase where there is no spontaneous magnetization along the $c$-axis. The zero-field transition displays a text-book example of a first order transition with different phase stability limits on heating and cooling. The results have special significance since ${\rm Fe}_2{\rm P}$ is the parent material to a family of compounds with outstanding magnetocaloric properties.