Abstract
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, {boldsymbol{simeq }} 12 nm, reveal a more complicated behavior. First, upon cooling the sample to intermediate temperature, {bf{T}}{boldsymbol{simeq }} 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, {bf{T}}{boldsymbol{simeq }} 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.
Highlights
Nanostructured prototypes of geometrically frustrated magnet have attracted lot of attentions in recent years[1,2]
The system undergoes a transition from paramagnetic spin gas state to the short-range ordered spin ice state, as manifested by the broad peak in resistance
It is followed by another short-range ordered magnetic charge configuration at further lower temperature
Summary
Nanostructured prototypes of geometrically frustrated magnet have attracted lot of attentions in recent years[1,2]. Contrary to the existing understanding that the temperature dependent evolution of magnetism results in unique magnetic phases in an artificial magnetic honeycomb lattice, new experimental investigations of nanostructured permalloy honeycomb lattice reveal the unusual coexistence of a long-range ordered state with short-range correlated magnetic charge ordered state at intermediate temperature of T = 175 K. It suggests that the system exhibits the tendency to develop competing states as the temperature is reduced below the paramagnetic spin gas phase. While the ultra-small element geometry ensures that the inter-elemental energy is small enough ( 15 K) to allow temperature to be a tuning parameter for the investigation of novel magnetic phases, the large sample size makes it suitable for the experimental research using macroscopic probes of small angle neutron scattering (SANS) and polarized reflectometry
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