The atomically sharp domain walls that were discovered by an international team led by researchers from the Institute of Physics of the Czech Academy of Sciences, might considerably improve the research of ulta-fast memory devices made from antiferromagnetic materials. Such devices can be more compact, and the data saved in them are better protected against any negative effects of external magnetic fields. The results have been published in Science Advances.
Devices based on magnetic materials have become an important part of our everyday lives. Magnets are essential for the generation and distribution of electricity, for data storage in cloud centres, and advances in magneto-electronic devices are also becoming increasingly important for high-speed memories in computers and smartphones.
To have the possibility to look inside the high-quality single crystals of an antiferromagnetic material composed of copper, manganese and arsenic (CuMnAs), researchers from the Institute of Physics teamed up with collaborators from CEITEC in Brno, University of Nottingham, University of Upsalla and Oak Ridge National Laboratory.
We had a rare opportunity to use the most state-of-the-art electron microscopes that use an electron beam to display the internal structure of materials on the atomic scale. In this case, apart from the structure, we observed the magnetic ordering of individual atoms.
Schematics of the atomically sharp domain walls at an antiphase boundary defect and in an unperturbed area of the CuMnAs single crystal, respectively. Symbols A (blue) and B (yellow) label the upper and lower Mn sublattices from the unit cell in (A). Thin dashed lines highlight preserved As atom matrix. Black arrows represent Lorentz force direction at individual sublattices, which focuses the deflected beam into the areas with light blue overlay.
When analysing the images, the researchers noticed that the periodic arrangement of atomic magnetic fields in the observed antiferromagnetic material altered abruptly. While in typical magnetic materials, where the change is gradual and extends over several hundreds or thousands of atoms, in this case the change was abrupt – from one atom to the neighbouring one, i.e. an atomically sharp magnetic domain wall.
In relation to the atomic domain walls, this discovery is ground-breaking for basic research as the existence of the walls brings a new perspective on our understanding of the effects in magnetic materials. At the same time the discovery sheds new light on microscopic mechanisms behind the functioning of ultrafast memory devices fabricated using some of the antiferromagnetic materials. The materials were first introduced by the research team from the Institute of Physics of the Czech Academy of Sciences in 2016 in Science and in 2021 in Nature Electronics.
Practicality of antiferromagnets demonstrated by spintronics
Antiferromagnets belong to the family of magnetic materials. The difference from ferromagnets is that the magnetic fields of the magnetic atoms in antiferromagnetic crystals compensate one another, i.e., point in opposite directions. Therefore, antiferromagnets neither stick to our fridge, nor do they have any of the interesting properties related to macroscopic fields generated by ferromagnets.
In 1970, when Louis Néel received his Nobel Prize in Physics for the discovery of antiferromagnets, he described them as interesting, but useless. Despite intense research efforts, that were motivated by Néel’s discovery, the potential for practical applications of antiferromagnets has indeed remained virtually unexplored, until the recent development of experimental antiferromagnetic spintronic devices.
While electronics relies on manipulation of electronic charge, spintronics also involves the manipulation of an additional intriguing property of electrons, their quantum spin. The internal magnetic structure of crystals is primarily due to the ordered state of electron spins, and special spin arrangements in antiferromagnets offer device concepts and functionalities unparalleled in ferromagnets.
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