Los Alamos National Laboratory
Gary Kliewer, (505) 665-2085/ [email protected]
EMBARGOED until Mar 19, 1997 at 1:30 p.m. Central Time
MICROSCOPIC 3-D IMAGING IN MATERIALS INTRODUCED KANSAS CITY, MO., Mar 19, 1997 -- A team of Los Alamos National Laboratory and Caltech scientists have made important breakthroughs in applying a powerful new technique that marries two existing technologies to probe materials at a microscopic level.
If researchers achieve their ultimate goals for this new technique it could have important applications in magnetic information storage technology.
Their device combines the techniques of magnetic resonance imaging, which has found powerful applications in the medical field, and atomic force microscopy, which can measure the surface structure of materials with microscopic sensitivity. Researchers call the new approach "magnetic resonance force microscopy."
Though research into this technology at Los Alamos and elsewhere is still in the early stages, the technology has already matched the sensitivity of current state-of-the-art magnetic resonance imaging technology and promises to achieve even better results.
"The ultimate goal is to be able to create three-dimensional images of materials in slices as small as one atom wide," said Los Alamos postdoctoral researcher Zhenyong Zhang.
Zhang described Los Alamos' efforts into magnetic resonance force microscopy at a press conference today at the American Physical Society meeting in Kansas City, Mo. (Zhang also will present a paper on his research Thursday at APS Session O3.)
Magnetic resonance technology provides scientists with information about the electronic structure and magnetic spin dynamics of a sample, but it offers limited sensitivity, which in turn limits the resolution that can be achieved with the technique. The atomic force microscope measures forces with such high sensitivity that it can determine surface structure with atomic-scale resolution.
By combining MRI with AFM to create a magnetic resonance force microscope, researchers can study the interior of a sample -- a crucial advantage over techniques sensitive to the surface only. If researchers reach their ultimate goal of single-spin sensitivity, then atomic-scale resolution with this technique will be within reach.
The technique is particularly well adapted for studying the interfaces in multi-layered, thin-film materials, which are increasingly important in electronic applications, such as disk readers in computers.
In collaboration with colleagues at Caltech, the Los Alamos researchers have made important breakthroughs in applying this powerful technology to the study of such materials.
Researchers expect that studies with magnetic resonance force microscopy will improve the understanding of how the performance of electronic devices can be affected by such key properties as the precision with which the interfaces are formed, the electronic coupling between materials in adjacent layers and interactions between magnetic properties of adjacent layers.
Magnetic resonance imaging, familiar for its medical applications, uses the selective absorption of very high-frequency radio waves, or resonance, by certain atomic nuclei to create three-dimensional images.
In contrast, magnetic force microscopy (a variant of atomic force microscopy) is a mechanical technique that uses a cantilever smaller than a human hair to reveal magnetic properties of a material's surface. The cantilever is bent slightly by the faint magnetic force, arising from the electronic spin of atoms in a sample. The researchers exploit the fact that a radio frequency -- similar to those generated for medical MRI -- excites spins at targeted points inside the material under investigation.
"When we add a radio-frequency excitation, the cantilever becomes specifically sensitive to subsurface regions," said Zhang. "We can then scan around inside the sample."
The device holds promise for application in many fields, but Zhang and Los Alamos staff member Chris Hammel, working with Caltech Professor Michael Roukes and his student Melissa Midzor, have focused on analysis of multi-layered thin films used in the magnetic disks in computers. Layers of magnetic material sandwiched with layers of non-magnetic layers such as copper or gold are used as variable resistors. The thickness and roughness of the interface between layers affects the performance of such devices. Magnetic resonance force microscopy, researchers expect, will be able to reveal the irregularities between the layers and the related local magnetism and electrical properties -- without having to cut or destroy the samples.
"Our goal is to achieve the sensitivity required to study the interface between layered magnetic materials with atomic-scale resolution," said Zhang. Understanding these interfaces is crucial for achieving increases in information storage density on magnetic disks.
Zhang will report on studies of yttrium-iron-garnet and cobalt thin film ferromagnets.
Los Alamos National Laboratory is operated by the University of California for the U.S. Department of Energy.
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