With the help of a new technology, Russian scientists have for the first time obtained a material for the manufacture of more stable permanent magnets capable of replacing expensive analogues with rare earth elements. The development is promising for use in electronics, audio and household appliances, as well as automotive and industrial applications.
Permanent magnets are widely used in electronics, medical equipment, sensors, generators, motor control systems, various automation mechanisms, for packaging and holding metal parts. Depending on the purpose, magnets are most often made of a neodymium-iron-boron alloy or hexagonal ferrites of barium or strontium. Neodymium magnets are the most powerful, but ferrite magnets are much cheaper, more affordable and more resistant to chemical influences and corrosion. An urgent task now is to improve the characteristics of ferrite magnets in order to replace neodymium magnets.
Researchers from NUST MISIS and the N.S. Kurnakov Institute of General and Inorganic Chemistry of the Russian Academy of Sciences have proposed their own alternative to expensive rare-earth magnets. First, they obtained a powder from barium hexaferrite nanoplates of a disc—shaped shape, which has a high coercive force - the magnitude of the external magnetic field strength necessary for the remagnetization of the substance.
"On average, the coercive force of commercially available and widely used grades of barium ferrites is up to 4 kE, less often — 5 kE. The powder we obtained has a coercive force of 5.6 kOe, which makes it superior to most known analogues," said Andrey Timofeev, PhD, Associate Professor of the Department of Materials Technology of Electronics at NUST MISIS.
To obtain a magnet, the powder must be sintered and subjected to high—temperature treatment
The researchers added bismuth oxide or boron oxide in varying amounts to the ferrite particles, and then the resulting mixture was molded and sintered at 900°C. Despite a slight increase in particle size, durable ceramic samples were obtained that retained their coercive force at a high level of 5.3 kOe.
"Scientists have been trying to improve the magnetic characteristics of hexaferrites using various methods for a long time. The uniqueness of our development lies in the combination of several technologies. The first is the production of hexaferrite nanoplates of a certain shape, which requires special synthesis conditions. The second is low—temperature sintering, which produces ceramics while maintaining the magnetic parameters of the initial powder. This material can later be used to create more efficient ferrite magnets," said Andrey Mironovich, PhD, Associate Professor at the Department of Materials Technology of Electronics at NUST MISIS.
The details of the study are published in the scientific journal Russian Journal of Inorganic Chemistry. The work was carried out within the framework of the strategic project of NUST MISIS "Materials of the Future" under the program "Priority 2030" (project K6-2022-043).
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