Simulating Spin Waves in Entropy Stabilized Oxides

TL;DR

This paper models spin wave excitations in entropy stabilized oxides, revealing a stable antiferromagnetic structure with a mixed coherent and incoherent spin-wave spectrum, using linear spin-wave theory and supercell approximation.

Contribution

It introduces a theoretical approach combining linear spin-wave theory and supercell approximation to analyze spin waves in highly disordered entropy stabilized oxides.

Findings

Antiferromagnetic order stabilized by rhombohedral distortion and second nearest neighbor interactions.

Spin-wave spectrum features a coherent low-energy mode within an incoherent continuum.

Theoretical results align with neutron scattering observations.

Abstract

The entropy stabilized oxide Mg$_{0.2}$Co$_{0.2}$Ni$_{0.2}$Cu$_{0.2}$Zn$_{0.2}$O exhibits antiferromagnetic order and magnetic excitations, as revealed by recent neutron scattering experiments. This observation raises the question of the nature of spin wave excitations in such disordered systems. Here, we investigate theoretically the magnetic ground state and the spin-wave excitations using linear spin-wave theory in combination with the supercell approximation to take into account the extreme disorder in this magnetic system. We find that the experimentally observed antiferromagnetic structure can be stabilized by a rhombohedral distortion together with large second nearest neighbor interactions. Our calculations show that the spin-wave spectrum consists of a well-defined low-energy coherent spectrum in the background of an incoherent continuum that extends to higher energies.