Science & Technology

Atomic Scale Imaging of Magnetic Structures

Magnetic order of iron tellurides, imaged with a low-temperature scanning tunneling microscope. The enlarged part reveals the atomic construction. Credit score: Peter Wahl, College of St Andrews & MPI for Strong State Analysis

Scientists from the Max Planck Institute for Strong State Analysis use atomic scale imaging of magnetic buildings to check new features of high-temperature superconductivity.

Superconductors increase many hopes, particularly supplies which lose their electrical resistance at fairly excessive temperatures – be it for high-performance medical imaging applied sciences, the power transportation or for maglev trains. Excessive-temperature superconductors which deserve the title may discover many purposes. Nonetheless, their fascination bears no relationship to the continued thriller of their precise nature; this has to this point hindered the seek for zero-resistance conductors for reasonable temperatures. Scientists from the Max Planck Institute for Strong State Analysis in Stuttgart and Augsburg are making their contribution to a extra detailed understanding of how iron-based superconductors work and the position performed by magnetism. They’re the primary to have imaged the magnetic construction of a so-called strongly correlated electron system, right here of iron telluride, on an atomic scale. Previous to this, details about the magnetic construction was supplied solely by neutron diffraction, however the picture it produced was imprecise. Iron telluride is the non-superconducting father or mother compound of the iron chalcogenide superconductors. The researchers now hope to have the ability to apply the strategy to supplies which exhibit each superconducting and magnetic properties as a way to discover out extra concerning the relationship between magnetism and superconductivity.

Substances reminiscent of copper oxide ceramics or iron arsenic compounds are deemed to be high-temperature superconductors: they don’t have to be cooled as a lot as different supplies as a way to render them superconducting. Why is that this? To this point there are hypotheses, however no confirmed description of the exact processes. “A key query which many analysis teams are actually posing is the one concerning the relationship between magnetic and superconducting properties of these supplies,” says Peter Wahl from the Max Planck Institute for Strong State Analysis and College of St Andrews. “Can each results happen at one and the identical location? Or are they mutually unique?” Physicists assume it’s attainable that the magnetic properties of the supplies may even be the trigger of their superconductivity.

With the intention to study this, researchers have lengthy been on the lookout for a process that permits characterization of the magnetic buildings in these strongly correlated digital supplies on the atomic scale. The strategy of neutron diffraction has to this point been the device of selection for investigating the magnetic order, but it surely supplies solely spatially averaged insights into the magnetic construction.

The Stuttgart-based Max Planck researchers have now made use of a so-called spin-polarized scanning tunneling microscope, which may picture the orientation of the magnetic moments of particular person atoms. The strategy is just not new, however has to this point principally been utilized to metallic surfaces and nanostructures. What was not clear till now was whether or not the strategy might be used to make clear the magnetic construction of a strongly correlated system reminiscent of iron telluride. It’s because the highest layer of this materials consists of tellurium, a component which itself is just not magnetic.

The scientists have now proven that the spin-polarized scanning tunneling microscope will also be utilized to strongly correlated electron supplies regardless of their advanced chemistry. The iron lattice under almost certainly exerts too nice an affect. Slender longitudinal stripes, which outcome from the anti-ferromagnetic order within the iron telluride, might be acknowledged within the picture taken by the scanning tunneling microscope. Inside the stripes, all magnetic moments have the identical orientation; on the adjoining stripes, it’s in the other way.

An experimental problem was to magnetize the tip of the microscope for the spin-polarized investigations. To review nanostructures on surfaces, researchers primarily achieved this by heating the tip of the microscope and vapor depositing magnetic materials on it. To keep away from the necessity for this technologically demanding process, the scientists used a trick: they picked up particular person iron atoms on the floor of the iron telluride underneath investigation with the tip of the microscope, till it turned magnetic. On this means, they might picture the magnetic stripe order in iron telluride with atomic decision in actual area.

The researchers made an attention-grabbing statement on the temperature which is critical for the anti-ferromagnetic construction to kind. Within the experiment, this was roughly minus 227 levels Celsius, round 20 levels decrease than the temperature that’s usually vital. The rationale for that is that the researchers noticed solely the floor of the iron telluride of their experiment. In comparison with the iron telluride layers within the bulk of the fabric, the interactions with an atomic layer above it are lacking right here. Consequently, the magnetic moments can’t mutually stabilize their order as effectively – the magnetic construction kinds solely at a decrease temperature.

The Analysis Group lead by Peter Wahl additionally decided that the magnetic order turns into extra advanced when the proportion of iron atoms is increased: the longitudinal stripes partially dissolve, and are overlaid by transverse stripes. Plainly the excess atoms and their magnetic moments mess up the magnetic. “There’s nonetheless an ideal potential for analysis right here,” says Peter Wahl. “I consider that an actual growth goes to develop very quickly, teams will likely be finishing up comparable experiments on different supplies on the boundary between superconductivity and magnetism.” Understanding the properties of these supplies could be step one in direction of superconducting expertise which is extra power environment friendly, and finally could even be appropriate for routine software.

Publication: Mostafa Enayat, et al., “Actual-space imaging of the atomic-scale magnetic construction of Fe1+yTe,” 2014, Science; DOI: 10.1126/science.1251682

Picture: Peter Wahl, College of St Andrews & MPI for Strong State Analysis
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