* PHYSICS/BK21 SEMINAR *

Magneto-electric multiferroicity in quantum magnetic insulators

연사
: Michel Kenzelmann

일시
: 물리학과 세미나실 (공학3동 201호)

일시
: 7월 11일 (수요일)  오후 15:00연 - 17:00

normal>Abstract

will talk about magnetic insulators in which the symmetry of the
spin
interactions leads to strong fluc-tuations and qualitatively new
ground
states. Of particular interest are frustrated quantum magnets in
which
long-range magnetic order is impeded because of competing interactions.
The
proximity of such systems to quantum critical points can lead to
strong
cross-coupling between magnetic order and the nuclear lattice. Case in
point
is a new class of multiferroic materials in which the magnetic
and
ferroelec-tric order parameters are directly coupled, and a magnetic
field
can suppress or switch the electric polari-zation [1]. Our
neutron
measurements reveal that ferroelectricity is induced by magnetic
order and
emerges only if the magnetic structure creates a polar axis [2-5].
The spin
dynamics and the field-temperature phase diagram of the ordered
phases
provide evidence that competing ground states are essential but
not
sufficient for ferroelectricity. The origin of the magneto-electric
coupling
is not under-stood at present, but it may arise from strain
derivatives of
the isotropic exchange interactions or anisot-ropic exchange
couplings such
as Dzyahloshinskii-Moriya interactions.