Spin-phonon coupling effects in transition-metal perovskites:a DFT+$U$ and hybrid-functional study

TL;DR

This study investigates spin-phonon coupling in transition-metal perovskites using DFT+$U$ and hybrid-functional methods, showing that DFT+$U$ can reliably predict phonon frequency shifts with less computational effort.

Contribution

The paper demonstrates that DFT+$U$ calculations fitted to hybrid-functional results accurately reproduce spin-phonon coupling effects in perovskites, offering a computationally efficient approach.

Findings

Phonon frequency shifts decrease with larger A cation radius in A$MnO_3$.

Frequency shifts vary with spin order in La$M$O$_3$, decreasing for some and increasing for others.

DFT+$U$ results align well with hybrid-functional calculations for spin-phonon coupling.

Abstract

Spin-phonon coupling effects, as reflected in phonon frequency shifts between ferromagnetic (FM) and G-type antiferromagnetic (AFM) configurations in cubic CaMnO$_3$, SrMnO$_3$, BaMnO$_3$, LaCrO$_3$, LaFeO$_3$ and La$_2$(CrFe)O$_6$, are investigated using density-functional methods. The calculations are carried out both with a hybrid-functional (HSE) approach and with a DFT+$U$ approach using a $U$ that has been fitted to HSE calculations. The phonon frequency shifts obtained in going from the FM to the AFM spin configuration agree well with those computed directly from the more accurate HSE approach, but are obtained with much less computational effort. We find that in the $A$MnO$_3$ materials class with $A$=Ca, Sr, and Ba, this frequency shift decreases as the A cation radius increases for the $\Gamma$ phonons, while it increases for R-point phonons. In La$M$O$_3$ with $M$=Cr, Fe, and Cr/Fe, the phonon frequencies at $\Gamma$ decrease as the spin order changes from AFM to FM for LaCrO$_3$ and LaFeO$_3$, but they increase for the double perovskite La$_2$(CrFe)O$_6$. We discuss these results and the prospects for bulk and superlattice forms of these materials to be useful as multiferroics.