A new study, led by the U.S. Department of Energy’s Argonne National Laboratory, has found that only half the atoms in iron-based superconductors are magnetic. This serves as conclusive proof of the wave-like properties of metallic magnetism in these materials.
The discovery gives us a better understanding of magnetism in some iron compounds and iron arsenide. It also shows how they might help to induce superconductivity, i.e., the resistance-free flow of electrical current through a solid-state material, which occurs at temperatures up to 138 degrees Kelvin, or -135 degrees Celsius.
“In order to be able to design novel superconducting materials, one must understand what causes superconductivity. Understanding the origin of magnetism is a first vital step toward obtaining an understanding of what makes these materials superconducting. Given the similarity to other materials, such as the copper-based superconductors, our goal was to improve our understanding of high-temperature superconductivity,” explained Argonne senior physicist Raymond Osborn, one of the project’s lead researchers.
“In terms of applications, such an understanding would allow for the development of magnetic energy-storage systems, fast-charging batteries for electric cars and a highly efficient electrical grid,” said Argonne senior physicist Stephan Rosenkranz, the project’s other lead researcher.
Superconductors reduce typical power loss in any electrical grid. The use of high-temperature superconducting materials in the electrical grid would significantly reduce this power loss and therefore boost efficiency of the power supply.
The researchers were able to show that the magnetism in these materials was produced by mobile electrons that are not bound to any particular iron atom, producing waves of magnetization throughout the sample. They also discovered that, in some iron arsenides, two waves cancelled each other out, producing zero magnetization in some atoms. This quantum interference, which has never been observed before, was revealed by Mössbauer spectroscopy, a highly magnetism-sensitive tool.
Researchers also used high-resolution X-ray diffraction at the Advanced Photon Source and neutron diffraction at Oak Ridge National Laboratory’s Spallation Neutron Source to determine the chemical and magnetic structures and hence map the electronic phase diagram of the samples used.
“By combining neutron diffraction and Mössbauer spectroscopy, we were able to establish unambiguously that this novel magnetic ground state has a non-uniform magnetization that can only be produced by itinerant electrons. These same electrons are responsible for the superconductivity,” Rosenkranz explained.
The research is available in the January 25 edition of Nature Physics.
As their next step Rosenkranz and Osborn plan to characterize the magnetic excitations or fluctuations of iron-based superconductors, to determine how they relate to each other and find out why they cause superconductivity.
Author: Aquiles Páez (@Aquiles_CFQ)
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