(Phys.org)—A team of researchers with
members from institutions in Spain, France and Egypt has demonstrated
that hydrogen atoms on graphene yield a magnetic moment and furthermore,
that such moments can order ferromagnetically over relatively large
distances. In their paper published in the journal Science the
group describes experiments they carried out in attempting to cause a
sheet of graphene to become magnetic, how they found evidence that it
was possible using hydrogen atoms, and the ways such a material might be
used in industrial applications. Shawna Hollen with the University of
New Hampshire, and Jay Gupta with Ohio State University, offer some
insights into the work done by the team in the same journal issue with a
Perspectives piece—they also outline the hurdles that still need to be overcome before magnetic graphene might be used in real applications.
Graphene's superior qualities as a material have been well
documented, though one of its drawbacks has not been highlighted as
much—it is not magnetic. If it were, it could conceivably be used in
many more applications. That has led to efforts to do things to a sheet
of graphene that would cause it to become magnetic, one of which is by adding hydrogen atoms to its surface, creating what has been called graphane.
Unfortunately, stability has been an issue, making the
process difficult to control. In this new effort, the researchers have
taken a different approach—they took advantage of the fact that
magnetism occurs in graphene when an imbalance occurs in two
sub-lattices that are part of the whole— that means the number of atoms
that exist in an individual sublattice can be caused to be unequal due
to such things as point defects or geometric shape. That allows a
hydrogen adatom to bond with a carbon pz-orbital. The end result is magnetic moments
being formed in the honeycomb lattice, with such moments aligning
ferromagnetically when they are on the same sublattice, and
antiferromagnetically when they are on an opposing sublattice.
Such a material, Hollen and Gupta note, might allow for
storing information at much higher densities than has ever been seen
before, but before that can happen, they also note, several hurdles must
be overcome, such as realizing atomic scale precision with the process
on a large scale.
Explore further:
Scientists make magnetic new graphene discovery
More information:
H. Gonzalez-Herrero et al. Atomic-scale control of graphene magnetism by using hydrogen atoms, Science (2016). DOI: 10.1126/science.aad8038
Abstract
Isolated hydrogen atoms absorbed on graphene are predicted to induce magnetic moments. Here we demonstrate that the adsorption of a single hydrogen atom on graphene induces a magnetic moment characterized by a ~20–millielectron volt spin-split state at the Fermi energy. Our scanning tunneling microscopy (STM) experiments, complemented by first-principles calculations, show that such a spin-polarized state is essentially localized on the carbon sublattice opposite to the one where the hydrogen atom is chemisorbed. This atomically modulated spin texture, which extends several nanometers away from the hydrogen atom, drives the direct coupling between the magnetic moments at unusually long distances. By using the STM tip to manipulate hydrogen atoms with atomic precision, it is possible to tailor the magnetism of selected graphene regions.
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