NUST MISIS specialists, together with colleagues from Lomonosov Moscow State University, synthesized a new alloy that can be used to create powerful permanent magnets without expensive rare earth metals, and determined its processing mode.
An alloy based on manganese and aluminum is considered to be one of the promising candidates as an alternative to powerful but expensive rare earth magnets needed in energy, electrical engineering and transportation systems. Its magnetic properties are related to the so-called t-phase. However, it is unstable: it easily collapses when the temperature or processing conditions change.
The authors found out how the behavior of such an alloy is affected by the addition of a small amount of vanadium and different cooling modes, from conventional quenching to ultrafast cooling of the melt on a rotating copper disk. Alloys with different manganese contents in the range of 51-55% were considered in the work.
"The composition and cooling mode allow for more precise control of the material structure. We found out that the addition of vanadium makes the magnetic t-phase less stable: it forms in a narrower range of compositions and collapses at a lower temperature. However, with ultrafast quenching, vanadium helps to obtain this phase without additional heat treatment," said Mikhail Gorshenkov, one of the authors of the study, associate professor of the Department of Physical Materials Science, leading researcher at the NUST MISIS Center for Infrastructural Interaction and Partnership MegaScience, Candidate of Technical Sciences.
Scientists have recorded the best result for an alloy based on manganese, aluminum and vanadium (Mn₅₃al₄₄v₃). After quenching and annealing, the proportion of the magnetic phase in the cast sample exceeded 90%. In thin metal films produced by ultrafast cooling, a high proportion of this phase was formed without additional heat treatment, which in the future will simplify the technology for obtaining the required ferromagnetic phase with a small grain size. The researchers also noted a slight increase in the magnetization of the ferromagnetic phase.
"Another interesting result is the detection of a hysteresis of the Curie temperature: the temperature of the ferromagnetic—paramagnetic phase transition when the sample was heated turned out to be more than 100 °C higher than when cooled. At the same time, no changes in the crystal structure of the material were observed. This effect is unusual for most ferromagnets and has not been observed previously on the alloys we are studying. We assume that the observed effect may be related to the occurrence of a magnetic phase transition by a mechanism of the first kind. We are currently studying this effect, as it may be useful for the production of various sensors," said another author of the work, an assistant at the NUST MISIS Department of Physical Materials Science. Anastasia Fortuna.
The research was carried out with the support of the Russian Science Foundation.
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