Determining the First Order Character of La(Fe,Mn,Si)13

TL;DR

This study employs microcalorimetry to precisely distinguish latent heat and heat capacity contributions in La(Fe,Mn,Si)13, advancing understanding of its magnetic transition's first order nature and introducing a model-independent parameter.

Contribution

It introduces a microcalorimetry-based method to quantify the first order character of magnetic transitions and proposes a new parameter for cross-material comparison.

Findings

Microcalorimetry detects an additional magnetic heat capacity peak due to Mn.

The method separates latent heat and heat capacity contributions.

A model-independent parameter for first order character is proposed.

Abstract

Definitive determination of first order character of the magnetocaloric magnetic transition remains elusive. Here we use a microcalorimetry technique in two modes of operation to determine the contributions to entropy change from latent heat and heat capacity separately in an engineered set of La(Fe, Mn, Si)13 samples. We compare the properties extracted by this method with those determined using magnetometry and propose a model independent parameter that would allow the degree of first order character to be defined across different families of materials. The microcalorimetry method is sufficiently sensitive to allow observation of an additional peak feature in the low field heat capacity associated with the presence of Mn in these samples. The feature is of magnetic origin but is insensitive to magnetic field, explicable in terms of inhomogeneous occupancy of Mn within the lattice resulting in antiferromagnetic ordered Mn clusters.