Magnetic Diode-type Rectification in an Artificial Honeycomb Lattice of Ultra-small Elements

The two-dimensional artificial magnetic honeycomb lattice system is evolving into a new research arena to explore a plethora of novel magnetism. We have created macroscopic samples of artificial magnetic honeycomb lattices of Permalloy having connected ultra-small elements (bonds), with length scales of sub-10 nm to 30 nm, which have never before been possible. The equivalent energy of the resulting systems is 10-100 K and is thus amenable to both temperature- and field-dependent exploration of novel magnetic phenomena. We have also performed detailed electrical measurements that have shown unidirectional electronic properties, analogous to a semiconductor diode. The unidirectional transport behavior, characterized by the asymmetric colossal enhancement in differential conductivity at a modest current application of 10-15 microamps, persists to T = 300 K in honeycomb lattice of thickness 6 nm. The asymmetric behavior arises without the application of magnetic field. A qualitative analysis of experimental data suggests the role of magnetic charge or monopoles in the unusual observations with strong implication for spintronics.