Artificial Spin Ice on the Kagome Lattice
John Cumings, U. Maryland.

Most materials are expected to become perfectly ordered at low
temperature, but some cannot, simply because the ordered state is not
a unique, low-energy state.  A famous example of this is ice, where
competing interactions prevent the hydrogen atoms from ordering at low
temperature.  Spin ice presents a promising new material for studying
this same physics, as the material is crystalline but still shows
analogous residual entropy due to magnetic disorder.  However, many
questions remain, in part because the spin configurations cannot be
directly imaged and therefore the role of crystal imperfections is not
understood.  Toward this end, a new model system has recently been
proposed and demonstrated that takes advantage of nano-lithography to
create interacting ferromagnetic patterns, dubbed "artificial spin
ice".  Interactions within these patterns are expected to reveal the
same physics, and results show a promising trend toward frustration.
I will present extensions of this work to a new lattice and show that
the resulting magnetic arrangements exhibit the perfect frustration
that one would expect for a similar T=0 spin ice.  This new
experimental realization stands poised to answer some of the questions
still open for frustration in general, such as the exact role of
crystal imperfections in sustaining or removing the disordered state.
Additionally, the new geometry presents an opportunity for exploring
the role that frustration might play in room-temperature ferromagnetic
systems, such as patterned-media memory storage devices.