Hot technology for cooling

Utilising magnetic molecules, the on-chip microrefrigeration systems could be expected to cool below the temperature of liquid helium, i.e., around 4 Kelvin or -269 degrees Celsius. Cooling of such materials via the magnetocaloric effect is achieved with a small change in applied magnetic field in the order of a few tesla.

Most studies of magnetic molecule-based coolers have been done on bulk materials. Extending the work to molecules deposited on a substrate is quite challenging both due to the low temperatures required and the weak magnetic signal of such small amounts of magnetic material. EU-funded researchers significantly advanced the state of the art for both bulk and substrate-deposited forms in the project MAPROMODE.

Two years of research into the physical characterisation at very low temperatures of certain molecule-based refrigerants in bulk form led to 10 publications in highly esteemed peer-reviewed journals.

In parallel, the team successfully deposited a molecular refrigerant on a silicon substrate. Researchers then characterised the grafted molecular refrigerants using advanced magnetic force microscopy (MFM). MFM is similar to atomic force microscopy (AFM) except it senses the magnetic surface properties through a magnetic force generated between the tip and surface.

Exploiting MFM at near-liquid helium temperature, scientists showed that the molecules maintain their magnetic properties and thus their cooling ability after deposition. The seminal work was published in a paper featured on the journal front cover and heralded in a university press release and the regional and national media. It is the first step toward realisation of cooling microchips on silicon operating at very low temperatures such as required by state of the art X-ray and infrared sensors.

The team continues to investigate ways to reduce the size of the refrigerators to the smallest scales to accommodate high-tech niche markets. The ground-breaking molecule-based microrefrigerator technology developed within MAPROMODE is set to be a hot commodity.