Antiferromagnetism in Ru2MnZ (Z=Sn, Sb, Ge, Si) full Heusler alloys: effects of magnetic frustration and chemical disorder

TL;DR

This study uses first-principles calculations and Monte Carlo simulations to understand antiferromagnetism in Ru2MnZ full Heusler alloys, highlighting the effects of chemical disorder and magnetic frustration on their magnetic properties.

Contribution

It introduces a comprehensive theoretical approach combining exchange interactions and disorder effects to explain antiferromagnetism in Ru2MnZ alloys, aligning with experimental data.

Findings

Ordered alloys (Z=Sn, Sb) match experimental Néel temperatures.

Chemical disorder significantly affects magnetic ordering in Si-based alloys.

Heat treatment could enhance Néel temperature by reducing atomic intermixing.

Abstract

We present systematic theoretical investigations to explore the microscopic mechanisms leading to the formation of antiferromagnetism in Ru2MnZ (Z= Sn,Sb,Ge,Si) full Heusler alloys. Our study is based on first-principles calculations of inter-atomic Mn-Mn exchange interactions to set up a suitable Heisenberg spin-model and on subsequent Monte-Carlo simulations of the magnetic properties at finite temperature. The exchange interactions are derived from the paramagnetic state, while a realistic account of long-range chemical disorder is made in the framework of the Coherent Potential Approximation. We find that in case of the highly ordered alloys (Z=Sn and Sb) the exchange interactions derived from the perfectly ordered L21 structure lead to N\'eel temperatures in excellent agreement with the experiments, whereas, in particular, in case of Si the consideration of chemical disorder is essential to reproduce the experimental N\'eel temperatures. Our numerical results suggest that improving a heat treatment of the samples to suppress the intermixing between the Mn and Si atoms, the N\'eel temperature of the Si-based alloys can potentially be increased by more than 30%. Furthermore, we show that in strongly disordered Ru2MnSi alloys a distinct change in the antiferromagnetic ordering occurs.