“Frustrated” spins in the magnetic field
Table of Contents
At this point Heinze and her team start. Studies suggest that such magnetically “frustrated” materials could be candidates for new coolant. “Frustrated quantum magnets form highly degenerate basic states that can be manipulated by pressure or external magnetic fields,” explain the physicists. Specifically, this means that such materials are used to make strong magnetic fields, this can lead to measurable temperature changes in the crystal – it reacts magnetocalorously.
Heinze and her colleagues have now examined in the experiment whether this is the case with Atacamit and how strong this effect is – with surprising results. If the desert mineral was exposed to a strongest pulsed magnetic field of 22 Tesla, it showed an unexpectedly strong cooling: its temperature dropped by almost half. This is exceptionally even for a magnetocaloric material, as the team explains.
Less instead of more magnetic order
But what is behind it? Additional analyzes provided a first note: “Using the magnetic spin resonance spectroscopy, we were able to clearly show that an invested magnetic field confuses the magnetic order in Atacamit,” explains co-author Tommy Kotte from the Dresden high field magnet laboratory. “This is unusual, since magnetic fields usually counteract frustration in many magnetic frustrated materials and even promote orderly magnetic conditions.”
The physicists found out why Atacamit behaves differently, in which they reconstructed the structure of the mineral and the reaction of its spins to magnetic influences. This revealed: The magnetic field arranges the copper ion spins on the tips of the saw tooth chains and reduces frustration as expected. “But because these spins also convey the three -dimensional coupling between the chains, their alignment on the external field breaks this coupling,” explain Heinze and her colleagues.
Temperature fall as an entropy compensation
This means that because the individual copper ion chains in the Atacamit are no longer connected to the neighboring chains via their spins, no magnetic order can no longer exist with large ranges. This changes the magnetic entropy in the mineral – and thus also its energetic balance, as the physicists explain. In order to compensate for this change in the entropy, the material must adapt its temperature accordingly.
This reaction explains the strikingly strong magnetocaloric effect of the Atacamit: it always occurs when a magnetic field influences the magnetic entropy of the system. And it is precisely this mechanism that the researchers have now proven directly in the Atacamit. “The physical mechanism we examined is fundamentally new and the observed magnetocaloric effect is surprisingly strong,” says Kotte.
Potential for new cooling methods
According to the research team, these findings could help develop new strategies for efficient cooling. Because magnetocalorous coolants do not need a compressor or the expansion of a refrigerant – a magnetic field is enough for you to lower your temperature. The desert mineral atacamit is rather not a question for such an application on a large scale – it is simply too rare and the breakdown is too complex.
But the decryption of the mechanism behind the cooling reaction of the desert mineral can now help to find other materials with a similar structure and reaction. “Our findings underline the potential of frustrated quantum magnets for coolant applications,” explain the physicists. (Physical Review Letters, 2025; DOI: 10.1103/Physrevlett.134.216701)
Source: Helmholtz Center Dresden-Rossendorf
2. July 2025 – Nadja Podbregar
