Scientists from the University of Connecticut, in collaboration with other researchers, have recently solved the mystery behind a distinct property in a unique magnetic metal. Ultimately this discovery could pave the way for the development of several new technologies such as more practical magnetic refrigeration and improved cooling systems for Magnetic Response Imaging (MRI) systems.
The research was in collaboration with Brookhaven National Laboratory and it was led by UConn Assistant Professor of Physics Jason Hancock and Brookhaven researcher Dr. Ignace Jarrige.
The investigation dealt primarily with the Kondo effect, which describes how magnetic impurities lead to scattering of electrons in different metals in response to changes in temperature. The material which was studied was ytterbium-indium-copper-four (YbInCu4), which has unique properties related to how its magnetism radically changes in response to a certain temperature.
“The screening in the Kondo effect happens below a certain ‘Kondo’ temperature, which is given for each material by its electronic properties,” Hancock said. “What is unusual about the material we studied (YbInCu4) is that the condo temperature value changes abruptly at 42K, from a very large value to a very small one.”
Using a groundbreaking synchrotron based analysis technique, researchers were able to prove that the cause of the switching behavior observed in YbInCu4 is caused by gaps in its energy spectrum.
“The new technique is called resonant inelastic X-ray scattering and was an idea brought by myself, our collaborator Akio Kotani, a theorist in Japan, and a scientist at Brookhaven named Ignace Jarrige,” Hancock said. “The existence of such a gap is unusual and was left out of Nobel-winning Ken Wilson’s considerations of the Kondo effect.”
Despite not being intentioned as applied research, the insight gained through the understanding of this unique property could ultimately lead to the development of several future technologies. Particularly, it could eventually lead to improvements in magnetic refrigeration techniques.
“As an alternative to magnetic refrigeration based on ferromagnets, one can also consider other types of phase transitions which strongly effect the magnetism. The magnetic response and temperature dependence of the strange Kondo-switching behavior of YbInCu4 does exactly this,” Hancock said.
The magnetic change associated with the Kondo effects occurs at a very low temperature (42K or -231 C) for YbInCu4, which makes this particular material impractical for commonplace refrigeration techniques. However, the insight into the cause of the observed switching behavior may allow researchers to discover materials where the switching occurs much closer to room temperature.
“If one were identified which had a transition near room temperature, you could imagine a magnetic refrigeration based AC unit which operates with high efficiency and zero noise. Such a miraculous invention could be aptly named an ‘air Kondo-itioner,’” Hancock said.