Research: Magnetic Cooling using a frustrated desert Mineral

Among the countless known minerals, some exhibit truly remarkable magnetic properties. One such example is the emerald-green mineral atacamite (Cu₂Cl(OH)₃), which was recently identified as a model system for so-called frustrated quantum magnets. Despite strong interactions between the magnetic copper ions, atacamite only exhibits magnetic order below 9 K due to the special geometry of the copper lattice—a phenomenon known as magnetic frustration.

In high-field experiments conducted at the Dresden High Magnetic Field Laboratory, researchers discovered a quantum critical point (QCP) at around 22 T. Using a combination of magnetization, specific heat, and nuclear magnetic resonance measurements, supported by numerical simulations, the team showed that this QCP marks the collapse of long-range magnetic order and a transition from three-dimensional to effectively one-dimensional magnetic behavior.

Because the temperature of the material changes significantly with variations in magnetic field near the QCP, these findings may also have relevance for future cooling technologies based on the magnetocaloric effect.

L. Heinze, T. Kotte, R. Rausch, A. Demuer, S. Luther, R. Feyerherm, E. L. Q. N. Ammerlaan, U. Zeitler, D. I. Gorbunov, M. Uhlarz, K. C. Rule, A. U. B. Wolter, H. Kühne, J. Wosnitza, C. Karrasch, S. Süllow,
Atacamite Cu₂⁢Cl⁢(OH)₃ in High Magnetic Fields: Quantum Criticality and Dimensional Reduction of a Sawtooth-Chain Compound,
Phys. Rev. Lett. 134, 216701 (2025) (arXiv)