Site-specific atomic substitution in a giant magnetocaloric Fe$_2$P-type system

TL;DR

This study investigates how site-specific vanadium substitution in a Fe2P-type magnetocaloric material affects its magnetic and magnetocaloric properties, aiming to reduce temperature hysteresis for better magnetic refrigeration performance.

Contribution

It provides the first detailed analysis of how substituting vanadium at specific metal sites influences the magnetic behavior and entropy change in (Fe,Mn)2(P,Si) compounds.

Findings

Significant difference in entropy change depending on site of vanadium substitution.

Vanadium site preference affects magnetic phase formation.

Lattice parameter changes influence magnetoelastic coupling.

Abstract

Giant magnetocaloric (GMC) materials constitute a requirement for near room temperature magnetic refrigeration. (Fe,Mn)$_2$(P,Si) is a GMC compound with strong magnetoelastic coupling. The main hindrance towards application of this material is a comparably large temperature hysteresis, which can be reduced by metal site substitution with a nonmagnetic element. However, the (Fe,Mn)$_2$(P,Si) compound has two equally populated metal sites, the tetrahedrally coordinated $3f$ and the pyramidally coordinated $3g$ sites. The magnetic and magnetocaloric properties of such compounds are highly sensitive to the site specific occupancy of the magnetic atoms. Here we have attempted to study separately the effect of $3f$ and $3g$ site substitution with equal amounts of vanadium. Using formation energy calculations, the site preference of vanadium and its influence on the magnetic phase formation are described. A large difference in the isothermal entropy change (as high as 44\%) with substitution in the $3f$ and $3g$ sites is observed. The role of the lattice parameter change with temperature and the strength of the magnetoelastic coupling on the magnetic properties are highlighted.