Magnetically induced phonon splitting in ACr$_2$O$_4$ spinels from first principles

TL;DR

This study uses first-principles calculations to analyze how magnetic ordering influences phonon splitting in ACr2O4 spinels, revealing that the sign of splitting depends solely on magnetic structure and can be described by a simple spin-phonon coupling model.

Contribution

It demonstrates that the sign of magnetically-induced phonon splitting is determined by magnetic order and validates a nearest neighbor exchange model for describing spin-phonon interactions.

Findings

The sign of phonon splitting varies with magnetic order.

The spin-phonon coupling can be modeled with only nearest neighbor exchange.

First-principles parameters accurately predict spin-phonon effects.

Abstract

We study the magnetically-induced phonon splitting in cubic ACr$_2$O$_4$ (A=Mg, Zn, Cd, Hg) spinels from first principles, and demonstrate that the sign of the splitting, which is experimentally observed to be opposite in CdCr$_2$O$_4$ compared to ZnCr$_2$O$_4$ and MgCr$_2$O$_4$, is determined solely by the particular magnetic ordering pattern observed in these compounds. We further show that this interaction between magnetism and phonon frequencies can be fully described by the previously proposed spin-phonon coupling model that includes only the nearest neighbor exchange. Finally, using this model with materials specific parameters calculated from first principles, we provide additional insights into the physics of spin-phonon coupling in this intriguing family of compounds.