  Artificial magnetic honeycomb lattice provides a two-dimensional archetypal
system to explore novel phenomena of geometrically frustrated magnets.
According to theoretical reports, an artificial magnetic honeycomb lattice is
expected to exhibit several phase transitions to unique magnetic states as a
function of reducing temperature. Experimental investigations of permalloy
artificial honeycomb lattice of connected ultra- small elements, ~ 12 nm,
reveal a more complicated behavior. First, upon cooling the sample to
intermediate temperature, T ~ 175 K, the system manifests a non-unique state
where the long range order co-exists with short-range magnetic charge order and
weak spin ice state. Second, at much lower temperature, T ~ 6 K, the long-range
spin solid state exhibits a re-entrant behavior. Both observations are in
direct contrast to the present understanding of this system. New theoretical
approaches are needed to develop a comprehensive formulation of this two
dimensional magnet.
