A novel approach
to designing artificial materials could enable magnetic devices with a wider
range of properties than those now available
The properties of a substance are largely dependent
on its constituent atoms and the way that these atoms interact with each other.
The finite number of atom types, however, imposes a limit on the range of
properties that a conventional material can have. In contrast, a new class of
engineered materials called metamaterials have no such limitation.
Metamaterials are typically composed of an array of
nanostructures that can interact with electromagnetic waves in much the same
way as atoms. In addition, the optical properties of these metamaterials can be
tuned by altering the size and shape of nanostructures.
An international team of researchers led by Boris
Luk'yanchuk at the A*STAR Data Storage Institute have now extended the
properties and potential uses of metamaterials by using not one but two very
different classes of nanostructures, or metamolecules1.
Luk'yanchuk and the team mathematically modelled a
two-dimensional array of metamolecules comprising a silicon sphere next to a
partially incomplete copper ring. They studied the influence of both the sphere
and the split ring on the magnetic component of an incident electromagnetic
wave — a property known as magnetization.
"When the two structures were more than one
micrometer apart, they both acted to increase the local magnetic field,"
says Luk’yanchuk. However, they started to interact when moved closer together,
and the researchers observed that the magnetization of the split ring decreases
and even becomes negative for separations smaller than 0.5 micrometers.
This situation is somewhat analogous to the
magnetic ordering in ‘natural’ materials. When all the atoms contribute in a
positive way to a material’s magnetic properties, the material becomes a
ferromagnet. However, when alternating regions of the material have opposite
magnetization, the material is said to be antiferromagnetic.
"We demonstrate that our hybrid lattices of
metamolecule exhibit distance-dependent magnetic interaction, opening new ways
for manipulating artificial antiferromagnetism with low-loss materials,"
explains Luk'yanchuk.
Although the analogy between metamaterials and
magnetic materials is not a perfect one, most metamaterials are said to be
ferromagnet-like. The design proposed by Luk'yanchuk and the team closely
mimics antiferromagnetic ordering, and this opens an opportunity for
researchers to study antiferromagnetic phenomena in metamaterials. One notable
example is giant magnetoresistance, a phenomenon that is at the heart of modern
electronic memories.
Luk'yanchuk affirms that a metamaterial analog
would offer exciting research prospects. "We believe that our work has the
potential to make a strong impact towards the development of on-chip integrated
solutions for reconfigurable and optically-controlled metamaterials."
The A*STAR-affiliated researchers contributing to
this research are from the Data
Storage Institute
References
- Miroshnichenko, A. E., Luk'yanchuk, B., Maier, S. A. &
Kivshar, Y. S. Optically induced interaction of magnetic moments in hybrid
metamaterials. ACS Nano 6, 837–842 (2012). | article
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