{"id":77217,"date":"2025-06-27T08:58:41","date_gmt":"2025-06-27T06:58:41","guid":{"rendered":"https:\/\/magazin.tu-braunschweig.de\/?post_type=kb_presseinformation&p=77217"},"modified":"2025-06-27T08:59:36","modified_gmt":"2025-06-27T06:59:36","slug":"magnetic-cooling-with-a-mineral-from-the-desert","status":"publish","type":"kb_presseinformation","link":"https:\/\/magazin.tu-braunschweig.de\/en\/pi-post\/magnetic-cooling-with-a-mineral-from-the-desert\/","title":{"rendered":"Magnetic cooling \u2013 with a mineral from the desert"},"content":{"rendered":"

Among the countless minerals known to science, there are always materials with unusual magnetic properties. One example is atacamite, which exhibits magnetocaloric behaviour at low temperatures \u2013 meaning that its temperature changes dramatically when a magnetic field is applied. This rare property has now been investigated by an international team led by Technische Universit\u00e4t Braunschweig and the Helmholtz-Zentrum Dresden-Rossendorf (HZDR). The results could contribute to the future development of new materials for energy-efficient cooling.<\/p>\n

The emerald-green mineral atacamite, named after the Atacama Desert in Chile where it was first discovered, owes its characteristic colour to copper ions, which also determine the material’s magnetic properties. Each ion has an unpaired electron whose spin gives the ion a magnetic moment – comparable to a tiny compass needle. \u201cWhat makes atacamite special is the arrangement of the copper ions,\u201d explains Dr Leonie Heinze from the J\u00fclich Centre for Neutron Science (JCNS), who won the Heinrich B\u00fcssing Prize at TU Braunschweig<\/a>. \u201cThey form long chains of small, interconnected triangles called sawtooth chains<\/strong>.\u201d This geometric structure has consequences: although the spins of the copper ions want to align antiparallel to each other in principle, this is not geometrically possible within the triangular arrangement. \u201cIn this case, we speak of magnetic frustration<\/strong>.\u201d As a result of this frustration, the spins in atacamite only arrange themselves into a static, alternating structure at very low temperatures – below 9 Kelvin (\u2212264\u00b0C).<\/p>\n

When the researchers investigated atacamite in the extremely high magnetic fields of the High Field Magnet Laboratory (HLD) at the HZDR, they made a surprising discovery: the material exhibited significant cooling in the pulsed magnetic fields – not just a slight decrease, but a reduction to almost half of the initial temperature. The researchers were particularly fascinated by this exceptionally strong cooling effect, as the behaviour of magnetically frustrated materials in this context has hardly been studied to date. Magnetocaloric materials are, however, considered a promising alternative to conventional cooling technologies<\/strong>, for example for energy-efficient cooling or the liquefaction of gases. Instead of compressing and expanding a coolant – a process that occurs in every refrigerator – they can be used to change the temperature by applying a magnetic field in a targeted manner, which is environmentally friendly and potentially low-loss.<\/p>\n

Where does this unexpectedly strong magnetocaloric effect come from?<\/h3>\n

Further investigations at various laboratories of the European Magnetic Field Laboratory (EMFL) revealed even deeper insights. \u201cUsing nuclear magnetic resonance spectroscopy, we were able to clearly demonstrate that an applied magnetic field disrupts the magnetic order in atacamite,\u201d explains Dr Tommy Kotte, a scientist at the High Field Magnet Laboratory in Dresden. \u201cThis is unusual, as magnetic fields in many magnetically frustrated materials usually counteract frustration and even promote ordered magnetic states.\u201d<\/p>\n

The team found an explanation for the mineral’s unexpected behaviour in complex numerical simulations carried out by Dr Roman Rausch and Prof Christoph Karrasch from the Institute of Mathematical Physics at Technical University of Braunschweig. The magnetic structure: The magnetic field aligns the magnetic moments of the copper ions at the tips of the sawtooth chains along the field, thereby reducing frustration as expected. However, it is precisely these magnetic moments that also mediate a weak coupling to neighbouring chains. When this coupling disappears, no long-range magnetic order can exist. This also enables the team to explain the strikingly strong magnetocaloric cooling effect, which always occurs when a magnetic field influences the disorder, or more precisely the magnetic entropy, of the system. In order to compensate for this rapid change in entropy, the material must adjust its temperature accordingly, cooling down significantly. And it is precisely this mechanism that the researchers have now demonstrated directly in atacamite.<\/p>\n

\u201cOf course, we don’t expect atacamite to be mined on a large scale in the future to build new cooling systems,\u201d explains Dr Tommy Kotte. \u201cBut the physical mechanism we investigated is fundamentally new, and the magnetocaloric effect we observed is surprisingly strong<\/strong>.\u201d The team hopes that their work will inspire further research, in particular the targeted search for innovative magnetocaloric materials within the extensive class of magnetically frustrated systems.<\/p>\n","protected":false},"excerpt":{"rendered":"

Among the countless minerals known to science, there are always … <\/p>\n","protected":false},"author":43,"featured_media":77205,"comment_status":"closed","ping_status":"closed","template":"","format":"standard","class_list":["post-77217","kb_presseinformation","type-kb_presseinformation","status-publish","format-standard","has-post-thumbnail","hentry","kb_cat_presse-research","kb_tags-materials","kb_tags-physics"],"acf":[],"yoast_head":"\nMagnetic cooling \u2013 with a mineral from the desert - TU Braunschweig | Blogs<\/title>\n<meta name=\"description\" content=\"Among the countless minerals known to science, there are always materials with unusual magnetic properties. 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