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

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

2011-12-21

arxiv.org/abs/1112.5205v2

Phys. Rev. B 85, 054417 (2012)

Physics

Condensed Matter

Strongly Correlated Electrons

13 pages, 7 figures, 9 tables

Scientific paper

10.1103/PhysRevB.85.054417

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.

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