  The nature of magnetic correlation at low temperature in two-dimensional
artificial magnetic honeycomb lattice is a strongly debated issue. While
theoretical researches suggest that the system will develop a novel zero
entropy spin solid state as T --> 0 K, a confirmation to this effect in
artificial honeycomb lattice of connected elements is lacking. We report on the
investigation of magnetic correlation in newly designed artificial permalloy
honeycomb lattice of ultra-small elements, with a typical length of ~ 12 nm,
using neutron scattering measurements and temperature dependent micromagnetic
simulations. Numerical modeling of the polarized neutron reflectometry data
elucidates the temperature dependent evolution of spin correlation in this
system. As temperature reduces to ~ 7 K, the system tends to develop novel spin
solid state, manifested by the alternating distribution of magnetic vortex
loops of opposite chiralities. Experimental results are complemented by
temperature dependent micromagnetic simulations that confirm the dominance of
spin solid state over local magnetic charge ordered state in the artificial
honeycomb lattice with connected elements. Our results enable a direct
investigation of novel spin solid correlation in the connected honeycomb
geometry of two-dimensional artificial structure.
