A proposed assembly of FeMg8 magnetic superatoms where the directions of magnetic moment is indicated by arrows. Image courtesy of Victor Medel/VCU. |
A team of Virginia Commonwealth University
scientists has discovered a new class of ‘superatoms’ – a stable
cluster of atoms that can mimic different elements of the periodic table
– with unusual magnetic characteristics.
The
superatom contains magnetized magnesium atoms, an element traditionally
considered as non-magnetic. The metallic character of magnesium along
with infused magnetism may one day be used to create molecular
electronic devices for the next generation of faster processors, larger
memory storage and quantum computers.
In
a study published online in the Early Edition of the Proceedings of the
National Academy of Sciences, the team reports that the newly
discovered cluster consisting of one iron and eight magnesium atoms acts
like a tiny magnet that derives its magnetic strength from the iron and
magnesium atoms. The combined unit matches the magnetic strength of a
single iron atom while preferentially allowing electrons of specific
spin orientation to be distributed throughout the cluster.
Through an elaborate series of theoretical studies, Shiv N. Khanna, Ph.D., a Commonwealth professor in the VCU Department of Physics,
and his team examined the electronic and magnetic properties of
clusters having one iron atom surrounded by multiple magnesium atoms.
The team included instructor J. Ulises Reveles and Victor M. Medel, a
post-doctoral associate, both from VCU; A. W. Castleman Jr., Ph.D., the
Evan Pugh Professor of Chemistry and Physics, and Eberly Distinguished
chair in Science in the Department of Chemistry at Penn State
University; and Prasenjit Sen and Vikas Chauhan from the Harish-Chandra
Research Institute in Allahabad, India.
“Our
research opens a new way of infusing magnetic character in otherwise
non-magnetic elements through controlled association with a single
magnetic atom. An important objective was to discover what combination
of atoms would lead to a species that is stable as we put multiple units
together,” said Khanna.
“The
combination of magnetic and conducting attributes was also desirable.
Magnesium is a good conductor of electricity and, hence, the superatom
combines the benefit of magnetic character along with ease of conduction
through its outer skin,” he said.
The
team found that when the cluster had eight magnesium atoms it acquired
extra stability due to filled electronic shells that were far separated
from the unfilled shells. An atom is in a stable configuration when its
outermost shell is full and far separated from unfilled shells, as found
in inert gas atoms. Khanna said that such phenomena commonly occur with
paired electrons which are non-magnetic, but in this study the magnetic
electronic shell showed stability.
According
to Khanna, the new cluster had a magnetic moment of four Bohr
magnetons, which is almost twice that of an iron atom in solid iron
magnets. A magnetic moment is a measure of the magnetic strength of the
cluster. Although the periodic table has more than one hundred
elements, there are only nine elements that exhibit magnetic character
in solid form.
“A
combination such as the one we have created here can lead to
significant developments in the area of “molecular electronics” where
such devices allow the flow of electrons with particular spin
orientation desired for applications such as quantum computers. These
molecular devices are also expected to help make denser integrated
devices, higher data processing, and other benefits,” said Reveles.
Khanna
and his team are conducting preliminary studies on the assemblies of
the new superatoms and have made some promising observations that may
have applications in spintronics. Spintronics is a process using
electron spin to synthesize new devices for memory and data processing.
This research was supported by the U.S. Department of Energy.
