Order--disorder induced magnetic structures of FeMnP$_{0.75}$Si$_{0.25}$

TL;DR

This study investigates how slight variations in crystallographic order in FeMnP$_{0.75}$Si$_{0.25}$ affect its magnetic properties, revealing significant changes from antiferromagnetic to ferrimagnetic behavior.

Contribution

It demonstrates the impact of order-disorder on magnetic structures in FeMnP$_{0.75}$Si$_{0.25}$, combining experimental synthesis with theoretical calculations.

Findings

Higher order leads to antiferromagnetism with zero net moment.

Disorder results in ferrimagnetic-like behavior with a net moment of 1.26 μB/f.u.

Theoretical calculations show large magnetic moments, especially Mn on pyramidal sites.

Abstract

We report on the synthesis and structural characterization of the magnetocaloric FeMnP$_{0.75}$Si$_{0.25}$ compound. Two types of samples (as quenched and annealed) were synthesized and characterized structurally and magnetically. We have found that minute changes in the degree of crystallographic order causes a large change in the magnetic properties. The annealed sample, with higher degree of order is antiferromagnetic with a zero net moment. The as-quenched sample has a net moment of 1.26 $\mu_B$/f.u. and ferrimagnetic-like behavior. Theoretical calculations give rather large values for the Fe and Mn magnetic moments, both when occupied on the tetrahedral and pyramidal lattice site. The largest being the Mn moment for the pyramidal site reaches values as high as 2.8 $\mu_B$/atom.