1112.5205 (Jiawang Hong et al.)

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

Jiawang Hong, Alessandro Stroppa, Jorge Íñiguez, Silvia Picozzi, David Vanderbilt

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.

View original: http://arxiv.org/abs/1112.5205