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Physicists trace the "hopping" of single electrons in magnetic materials
Spintronic Materials Show Their First Move
Los Angeles, CA | March 22, 2005
How much energy does it take for an electron to
hop from atom to atom, and how do the magnetic properties of the
material influence the rate or ease of hopping? Answers to those
questions could help explain why some materials, like those used in a
computer hard drive, become conductors only in a magnetic field while
they are very strong insulators otherwise. They might also help
scientists learn how to use the electron's "spin" (a property
analogous to the spinning of a child's toy top), as well as its
charge, to carry information in a new field known as spintronics.
Stéphane Grenier, a postdoctoral fellow studying electronic
excitations, or "electron hopping," at the U.S. Department of
Energy's Brookhaven National Laboratory, will describe the techniques
he uses and the properties of these materials at the March 2005
meeting of the American Physical Society in Los Angeles, California.
His talk will take place on Monday, March 21, at 2:30 p.m. in room
151 of the Los Angeles Convention Center.
"We are looking at something very local, electrons hopping between a
pair of atoms, to help us understand important macroscopic effects,"
Grenier says. "This information could help predict which materials
might have the properties needed for particular applications -- say,
increasing the storage capacity of computer hard drives -- and direct
the fabrication of new materials in which these properties are
To determine the energy needed by an electron to hop from one atom to
another atom, Grenier used a technique called inelastic x-ray
scattering at the Advanced Photon Source at Argonne National
Laboratory. He shines x-ray light onto the sample and measures the
tiny difference in
energy between the incoming and outgoing photons. This difference is
the amount of energy needed to move the electrons.
He used this technique to study materials with different magnetic
"lattices" -- ferromagnetic and antiferromagnetic. In ferromagnetic
materials, the atoms' magnetic moments (that is, their spins) are all
aligned in the same direction. In antiferromagnetic materials, the
magnetic moments of the adjacent atoms point in opposite directions.
"When the magnetic moments are aligned, the electron hopping is
increased between particular atoms. That is, more electrons make the
jump to their neighbors, and it takes less energy to move them,"
Grenier says. "While this has been known for a while, we have shown
the direction in which the electrons move and exactly what price they
'pay,' in terms of energy, to move, and the influence the magnetic
lattice of the material has on this hopping."
The electrons want to align their own magnetic moments, or spins,
with that of the atoms in the lattice, he explains. "They will do so
only if all the atoms' magnetic moments are aligned -- that is when
the 'fare' for hopping has its lowest price," he said.
Electrons moving with their spins aligned in the same direction make
a current of spins, which could be used, somewhat like currents of
electrical charge are now used, to pass or transform information in
future electronic components made of tailored magnetic lattices -- a
future generation of circuits based on the science of "spintronics,"
which is also carried out at Brookhaven Lab.
Grenier's studies, along with theoretical analysis of the materials,
may also help scientists understand why some materials possess
properties such as superconductivity and "colossal
magnetoresistance," the ability of some strong insulators to become
good conductors when induced by a magnetic field.
Studies on atomic magnetism have applications for understanding novel
materials -- including spintronic materials and superconductors --
that will revolutionize the electronic and energy industries. Such
studies using x-rays can only be performed in the U.S. at x-ray
synchrotron radiation facilities built and managed by the U.S.
Department of Energy's Office of Science.
This research was funded by the Office of Basic Energy Sciences
within the U.S. Department of Energy's Office of Science.
One of the ten national laboratories overseen and funded primarily by
the Office of Science of the U.S. Department of Energy (DOE),
Brookhaven National Laboratory conducts research in the physical,
biomedical, and environmental sciences, as well as in energy
technologies and national security. Brookhaven Lab also builds and
operates major scientific facilities available to university,
industry and government researchers. Brookhaven is operated and
managed for DOE's Office of Science by Brookhaven Science Associates,
a limited-liability company founded by Stony Brook University, the
largest academic user of Laboratory facilities, and Battelle, a
nonprofit, applied science and technology organization. Visit
Brookhaven Lab's electronic newsroom for links, news archives,
graphics, and more: www.bnl.gov/newsroom
Karen McNulty Walsh
Mona S. Rowe
Copyright © BNL
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