Spin Solid versus Magnetic Charge Ordered State in Artificial Honeycomb Lattice of Connected Elements

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.