Abstract
Multiferroic materials allow the electric polarization
to be controlled by switching the direction
of magnetic ordering and consequently
offer prospects for many new technological applications
[1–4]. Because multiferroic behavior
has been found in materials that exhibit complex
(non-collinear and incommensurate) magnetic
order, it is essential to know the spin arrangement
of the ground states in these materials
[4–9]. In many cases, elastic neutron scattering
measurements alone are not sufficient to
distinguish among several potential complex magnetic
states. We report inelastic neutron scattering
(INS) measurements that provide a distinct
dynamical fingerprint for the multiferroic ground
state of 3.5% Ga-doped CuFeO2. The complex
ground state is stabilized by the displacement of
the oxygen atoms [10], which are also responsible
for the multiferroic coupling predicted by Arima
[8]. By comparing the observed and calculated
spectrum of spin excitations, we conclude that
the magnetic ground state is a distorted screwtype
spin configuration. The exchange interactions
that stabilize this structure are consistent
with those obtained from inelastic measurements
[11, 12] on undoped CuFeO2.
