Identifying the magnetic structure of a material is a key to unlocking new features and better performance in electronic devices. However, the resolution of increasingly complex magnetic structures requires increasingly sophisticated approaches.
Researchers at the Center for Materials Crystallography at Aarhus University in Denmark are developing a new technique for solving highly sophisticated magnetic structures using neutrons at the Department’s Oak Ridge National Laboratory (ORNL) of energy (DOE). Their goal is to develop the technique – based on the mathematical analysis of large three-dimensional diffraction data – to establish a basic approach that can be adapted to a large class of magnetic materials with different structures.
âIn magnetic materials, many atoms have a magnetic moment, or spin, which acts like a very small magnet. In typical magnets, like refrigerator magnets, each of them is aligned in the same direction and they are combine to form a larger magnetic moment, which allows us to stick objects on our refrigerator. This is an example of an ordered magnetic structure, where a specific pattern is repeated over and over, “said Nikolaj Roth, researcher at Aarhus. âBut we’re more interested in disordered systems, or frustrated magnetism, where there is no long-range magnetic order. Where there is no fixed, repeating pattern of spins. This is where all kinds of interesting things happen. “
While “frustrated” or messy magnetism may seem haphazard or even chaotic, “it isn’t,” Roth explained. There are correlations between spins, if only for a short distance, called a short-range magnetic order. If the dynamic properties of frustrated magnetism can be harnessed, these materials could be used to develop new electronics with extremely advanced capabilities. This, of course, depends on the ability to identify short-range correlations in magnetic materials faster, more efficiently, and on a much larger scale.
âA few years ago, we developed a new data analysis technique that made it very easy to see these close-range correlations,â said Roth.
In early experiments, the team succeeded in calculating magnetic correlations in a sample of bixbyite, a manganese-iron oxide material found in Utah. In this follow-up experiment, they used bixbyite from South Africa which has a different manganese / iron ratio and therefore has a slightly different magnetic structure.
“We have the help of Mother Nature in that we don’t have to synthesize these materials, they are just in the soil,” said researcher Kristoffer Holm. âThe Utah sample is about 50:50 manganese iron, while the South Africa sample is closer to 70:30. These are very closely related samples, and we hope they will be able to tell us how the differences in composition will affect their close-range correlations.
Neutrons are well suited for studying magnetic behavior because the particles themselves act like tiny magnets. Neutrons can penetrate many materials deeper than other complementary methods; and because they have no charge, they interact with samples without compromising or damaging material to reveal critical information about energy and matter at the atomic scale.
By themselves, the compositions of pure iron and pure manganese have ordered structures at low temperatures, to which their spins are aligned in a specific repeating pattern. But when combined, they become disordered and form a “spin glass” state below 30 Kelvin (about minus 400 Â° Fahrenheit), where a complex pattern of spin alignments attaches itself.
The short range magnetic order has a weak signal and is difficult to detect with conventional neutron scattering instruments. However, ORNL’s spallation neutron source (SNS) CORELLI beamline provides a high flux, or large number of neutrons, with an array of detectors that can capture large volumes of data quickly and with high speeds. unprecedented detail. Using CORELLI, the team was able to quantify the magnetic structure of the South African bixbyite sample to make comparisons between it and the atomic structure of the material.
âCORELLI is the only instrument in the world that could do this experience as we need it to. It allows us to measure in all directions, even at high angles, and it does so very quickly, which is exactly what we need for the technique we are developing, âsaid researcher Emil Klahn. “Even if we could do it at another facility, it would take weeks to do what we were able to do in just a few days.”
The team says that with a fully developed technique, they will be able to study similar materials that exhibit bizarre and unusual behaviors or states of matter; candidate materials include quantum spin liquids, spin ice and unconventional superconductors. In turn, this information could lead to a wide range of radically advanced electronic applications.
Visualization of strong magnetic fields with neutrons
Quote: Obtaining Order in the “Frustrated” Landscape of Disordered Magnetism (November 7, 2019) retrieved September 26, 2021 from https://phys.org/news/2019-11-frustrated-landscape-disordered-magnetism.html
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