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APS March Meeting 2011

## Volume 56, Number 1

##
Monday–Friday, March 21–25, 2011;
Dallas, Texas

### Abstract: H17.00009 : Canted-spin-caused electric dipoles: a local symmetry theory

10:00 AM–10:12 AM

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A pair of magnetic atoms with canted spins ${\rm {\bf S}}_a
\,\mbox{and}\,{\rm {\bf S}}_b $can give rise to an electric dipole
moment \textbf{P. } Several forms for the dependence of \textbf{P} on the
spins have been derived from various microscopic models, some of which have
been invoked to explain experimental results found in some multiferroic
materials. The forms are ${\rm {\bf P}}_1 \propto {\rm {\bf
R}}\times ({\rm {\bf S}}_{\rm {\bf a}} \times {\rm {\bf S}}_b ),\,{\rm {\bf
P}}_2 \propto {\rm {\bf S}}_{\rm {\bf a}} \times {\rm {\bf S}}_b ,\,{\rm
{\bf P}}_3 \propto {\rm {\bf S}}_{\rm {\bf a}} ({\rm {\bf S}}_{\rm {\bf a}}
\cdot {\rm {\bf R}})-{\rm {\bf S}}_b ({\rm {\bf S}}_b \cdot {\rm {\bf R}})$,
where \textbf{R} is the relative position of the atoms. To unify and
generalize these various forms we consider \textbf{P }as the most general
quadratic function of the spin components that vanishes whenever ${\rm {\bf
S}}_{\rm {\bf a}} \,\mbox{and }{\rm {\bf S}}_b $are collinear. The study
reveals new forms. We generalize
to the vector \textbf{P}, Moriya's symmetry considerations on the (scalar)
DM energy ${\rm {\bf D}}\cdot {\rm {\bf S}}_{\rm {\bf a}} \times {\rm {\bf
S}}_b $(which led to restrictions on \textbf{D}). This provides a rigorous
proof that \textbf{P}$_{1}$ is allowed no matter how
high the symmetry of the atoms plus environment, and gives restrictions for
all other contributions. The
analysis leads to the suggestion of new terms omitted in the existing
microscopic models, and predicts an
unusual antiferroelectric ordering in the antiferromagnetically and
ferroelectrically ordered phase of RbFe(MoO$_{4})_{2}$.

To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2011.MAR.H17.9