Summary: Condensed Matter Colloquium
Thursday, September 22, 2011
2 pm, Room 1201
Refreshments at 1:30 pm in Room 1305F
Jeffrey W. Lynn
NIST Center for Neutron Research
Frustrated Magnets, Spin Ice,
and the Emergence of Magnetic Monopoles
Frustrated magnets--ones that have competing interactions--are especially
sensitive to perturbations, and can exhibit novel magnetic ground states that
are fundamentally different than conventional long range magnetic order. We
will discuss results on kagomé lattice and kagomé staircase systems, which
reveal rich phase diagrams as a function of temperature and magnetic field.
We will also discuss frustrated cubic magnets such as spinels and pyrochlores.
For the latter materials, typified by Dy2Ti2O7, the rare earth ions form a corner-
sharing tetrahedral network. The very special magnetic anisotropy of the Dy3+
spins requires them to point along a local <111> axis, such that on each
tetrahedron the moment can only point into the center, or in the opposite
direction. The ground state then turns out to be where two spins on each
tetrahedron point inward, and two point outward--a spin version of ice.