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Monday, 30 September 2013

Molecular coolers get Adv. Mater. front cover story

ICN2 and INA researchers make the front cover of the June 4th issue of Advanced Materials, which features an experimental study of the magnetic stray field.

The front cover story of the June 4th issue of Advanced Materials features an experimental study of the magnetic stray field originated by molecular coolers deposited on a silicon substrate, by means of quantitative Magnetic Force Microscopy (qMFM) at liquid-helium temperatures. The artwork (see Figure) represents droplets of the molecular complex gadolinium acetate tetrahydrate on silicon.

An important activity in low-temperature physics deals with the development of new technologies, based on micron-sized devices (microchips) that could replace the complex and bulky refrigerators that are currently used. It is hoped that in a not-too-distant future such microchips can be used as cooling platforms in all kinds of experiments that require temperatures close to absolute zero, e.g., for gamma and X-ray detection in astronomy, materials science or safety instrumentation.

Magnetic refrigeration based on the use of molecule-based magnetic materials is among the technologies that compete in such a race. Each magnetic material shows a phenomenon known as the magnetocaloric effect (MCE), whereby the temperature varies in response to the application of an external magnetic field. Magnetic molecules can possess an extraordinarily high MCE in the temperature range close to absolute zero. Besides, the versatility of the molecules is such as to allow “anchoring” them to a surface, forming thin deposits or monolayers. This is a mandatory step for obtaining cooling microchips based on silicon (the ideal material for manufacturing the devices), capable of exploiting the features of such materials. However, to date, there was no experimental evidence that the molecules, once deposited on Si, would preserve their magnetic characteristics, and therefore, their ability to cool.

A team of researchers from the Institute of Materials Science of Aragón, Institute of Nanoscience of Aragón, Physical Measurement Service of the University of Zaragoza and the Institut Catala de Nanociencia i Nanotecnologia in Barcelona, has obtained this important challenge for the first time. The material chosen is gadolinium acetate tetrahydrate, i.e., a molecular material characterized by a simple dinuclear core. In a previous study [Angew. Chem. Int. Ed. 2011, 50, 6606], this same material was shown to have a MCE even larger than the magnetic nanoparticles and alloys heretofore employed as refrigerants at very-low temperatures. In the present work, this team has deposited gadolinium acetate tetrahydrate on silicon by Dip-Pen Nanolithography (DPN) and measured the surface magnetism at liquid-helium temperatures. The result leaves no doubt: the deposition process does not alter the excellent cooling power of the molecules.

For more information on the new photochromic film, please contact:

Prof Daniel Ruiz - Group Leader

Nanostructured Functional Materials Group, ICN2

Tel: 93 737 36 14

E-mail: dani.ruiz@cin2.es

Surface-confined molecular coolers for cryogenics, G. Lorusso, M. Jenkins, P. Gonzalez-Monje, A. Arauzo, J. Sesé, D. Ruiz-Molina, O. Roubeau, and M. Evangelisti