Charge ordering of magnetic dipoles in artificial honeycomb patterns

Artificial spin ice offers the possibility to investigate a variety of dipolar orderings, spin frustrations and ground states. We have investigated magnetic dipoles arranged on a honeycomb lattice as a function of applied field, using magnetic force microscopy. The patterns were prepared by electron beam lithography where the basic units are polycrystalline Fe islands with dimensions length, width, and thickness of 3 mu m, 0.3 mu m, and 20 nm, respectively. These islands are in a single domain dipolar state at remanence. We have measured the magnetization reversal of the honeycomb patterns with different field directions. For the easy direction with the field parallel to one of the three dipole sublattices we observe at coercivity a maximum of magnetic charge order of alternating charges +/- 3, where the magnetic charge refers to the number and sign of magnetic poles pointing into any of the vertices. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3463482]