Local magnetic and geometric structure in Mn-doped La(Fe,Si)13

TL;DR

This study investigates how Mn doping affects the magnetic and structural properties of La(Fe,Si)13, revealing increased disorder and changes in magnetic polarization, which are crucial for optimizing magnetocaloric materials for cooling applications.

Contribution

It provides detailed insights into the local magnetic and geometric structure changes in Mn-doped La(Fe,Si)13 using advanced spectroscopic techniques and first-principles calculations.

Findings

Decreased magnetic polarization at Fe K edge with Mn doping.

Increased positional disorder around La atoms.

Enlarged Mn-Si distance explains increased disorder.

Abstract

Magnetic cooling has the potential to replace conventional gas compression refrigeration. Materials such as La(Fe,Si)$_{13}$ exhibit a sizeable first-order magnetocaloric effect, and it is possible to tailor the phase transition towards room temperature by Mn-H-doping, resulting in a large temperature range for operation. Within this work, we discuss variations of the electronic and lattice structure in La(Fe,Si)$_{13}$ with increasing Mn content utilizing X-ray magnetic circular dichroism (XMCD) and extended X-ray absorption fine structure spectroscopy (EXAFS). While XMCD shows a decrease of the magnetic polarization at the Fe K edge, low-temperature EXAFS measurements indicate increased positional disorder in the La environment that is otherwise absent for Fe and Mn. First-principles calculations link the positional disorder to an enlarged Mn-Si distance -- explaining the increased positional disorder in the La surrounding.