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Condensed Matter Seminars
| Condensed Matter
Thursday, October 12, 2006
Physics Building, Room 204
Note special time.
Note special room.
[Host: Seunghun Lee]
UC Santa Barbara
"Magnetic ordering in a half--polarized magnetization plateau of the pyrochlore antiferromagnet"
The classical pyrochlore antiferromagnet (AFM) is considered the
``most'' geometrically frustrated system. Classically, this leads to the
absence of any ordering transition at non-zero temperature, even in an
applied magnetic field. Recent experiments on the spinel chromites, ACr2o4(A=Cd,Hg) show the existance of a very robust magnetization plateau in a
strong magnetic field, and a simultaneous magnetic ordering.
We describe a model of spin-lattice coupling that explains both the
plateau formation and the observed ordering on the plateau. The predictions are confirmed by recent neutron scattering and x-ray
scattering experiments (S. H. Lee et al.). The same model applied to
zero magnetic field predicts a reduced
but still large ground state degeneracy, including the states observed
in both the Cd and Hg materials. This is consistent with the dominance
of spin-lattice interactions, with weak additional effects determining
the low field magnetic ordering.
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