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Topic Name: DOE Researchers Discover Surface Orbital "Roughness" in Manganites
Category: Chemical
Research persons: John Hill
Location: Brookhaven National Laboratory, DOE, United States
Details
Researchers at the U.S. Department of Energy's Brookhaven
National Laboratory have shown that in a class of materials called
manganites, the electronic behavior at the surface is considerably different
from that found in the bulk. Their findings, which were published online in the
November 18, 2007, issue of Nature Materials, could have implications for the
next generation of electronic devices, which will involve increasingly smaller
components.
As devices shrink, the proportion of surface area grows in comparison to the
material's volume. Therefore, it's important to understand the characteristics
of a material's surface in order to predict how those materials behave and how
electrons will travel across an interface, said Brookhaven physicist John Hill.
Hill and his fellow researchers were particularly interested in how the outer
electrons of atoms in a so-called manganite material are arranged. Manganites -
consisting of a rare-earth element such as lanthanum combined with manganese and
oxygen - show a huge change in electrical resistance when a magnetic field is
applied. Taking advantage of this "colossal magnetoresistance effect"
could be the key to developing advanced magnetic memory devices, magnetic field
sensors, or transistors.
The research team, which also includes scientists from KEK
(Japan), CNRS (France), Ames
Laboratory, and Argonne National Laboratory,
used x-ray scattering at Brookhaven's National Synchrotron Light Source and
Argonne's Advanced Photon Source to study the orbital order - the arrangement of
electrons in the outermost shell - of the material at the surface and in its
bulk.
"When you cool down the bulk material to a particular temperature, all
the orbitals arrange themselves in a very particular pattern," Hill said.
"The question is, does the same thing happen at the surface? And if not,
how is it different?"
The authors found that at the surface, the orbital order is more disordered
than in the bulk material. And, even though the manganite's crystal surface is
atomically smooth, the orbital surface is rough. These characteristics could
affect the way electrons are transferred across a material's surface and provide
fundamental information for future research and development. Next, the
researchers plan to look for this surface orbital "roughness" in other
materials and test its effect on magnetism.
Funding for this research was provided by the Office of Basic Energy Sciences
within in the U.S. Department of Energy's Office of Science.
Note for Manganite
Manganite is a mineral. Its composition is manganese oxide-hydroxide, MnO(OH), crystallizing in the orthorhombic system and isomorphous with diaspore and goethite. Crystals are prismatic and deeply striated parallel to their length; they are often grouped together in bundles. The color is dark steel-grey to iron-black, and the luster brilliant and submetallic. The streak is dark reddish-brown. The hardness is 4, and the specific gravity is 4.3. There is a perfect cleavage parallel to the brachypinacoid, and less-perfect cleavage parallel to the prism faces. Twinned crystals are not infrequent.
The mineral contains 89.7% manganese sesquioxide; it dissolves in hydrochloric acid with evolution of chlorine. The best crystallized specimens are those from Ilfeld in the Harz, where the mineral occurs with calcite and barite in veins traversing porphyry. Crystals have also been found at Ilmenau in Thuringia, Neukirch near Schlett stadt in Alsace (newkirkite), Granam near Towie in Aberdeenshire, and in Upton Pyne near Exeter, UK and Negaunee in Michigan, United States. As an ore of manganese it is much less abundant than pyrolusite or psilomelane.
Note for X-ray scattering techniques
X-ray scattering techniques are a family of non-destructive analytical techniques which reveal information about the crystallographic structure, chemical composition, and physical properties of materials and thin films. These techniques are based on observing the scattered intensity of an x-ray beam hitting a sample as a function of incident and scattered angle, polarization, and wavelength or energy.
About the Office of Science
The Office of Science is the single largest supporter of basic research in the physical sciences in the United States, providing more than 40 percent of total funding for this vital area of national importance. It oversees – and is the principal federal funding agency of – the Nation’s research programs in high-energy physics, nuclear physics, and fusion energy sciences.
The Office of Science manages fundamental research programs in basic energy sciences, biological and environmental sciences, and computational science. In addition, the Office of Science is the Federal Government’s largest single funder of materials and chemical sciences, and it supports unique and vital parts of U.S. research in climate change, geophysics, genomics, life sciences, and science education.
The Office of Science manages this research portfolio through six interdisciplinary program offices: Advanced Scientific Computing Research, Basic Energy Sciences, Biological and Environmental Research, Fusion Energy Sciences, High Energy Physics and Nuclear Physics. In addition, the Office of Science sponsors a range of science education initiatives through its Workforce Development for Teachers and Scientists program.
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