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Posted: May 18, 2009

Magnetic refrigeration key to next generation of energy-saving household appliances

(Nanowerk News) Energy-guzzling refrigerators and air-conditioning units may become a thing of the past, thanks to 'magnetic' research conducted by scientists at the UK's Imperial College London in collaboration with Iowa State University in the US. Magnetic refrigeration technology may signal a new era in environmentally friendly fridges and air-conditioning systems, slashing the staggering amounts of energy that they currently consume by up to 30%. The new findings were published in the journal Advanced Materials (Metamagnetism Seeded by Nanostructural Features of Single-Crystalline Gd5Si2Ge2).
The concept of magnetic refrigeration is straightforward. Heat is created when a magnetic field is applied to magnetic materials, such as metallic alloys. Water is then used to cool the material down, allowing it to return to its original temperature. The temperature of the material falls further when the magnetic field is removed altogether. It is the potential of this cooling property that researchers are targeting and which they believe could be used in a range of products.
In fact, researchers have proved that the technology works, but in order to take it out of the lab and into homes they still need to find the right material. This material needs to be highly efficient at cooling under normal room temperatures and to operate well under everyday conditions. In addition, its efficiency should not be compromised when the cooling cycle is repeated over and over again.
The magnetic cooling field is not new. The authors of the study indicate that it was first conceived in the 1920s, and it has only been in the last decade that the field has experienced a resurgence in interest due to the discovery of giant magnetocaloric effects (i.e. the heating up of magnetic materials when placed in a magnetic field, and their cooling down when removed from a magnetic field) in a group of materials known as metamagnets. These are 'compounds that undergo a first-order transition to a magnetically ordered state, often accompanied by a coincident transformation of the crystal structure,' the study reads.
Research undertaken by the Imperial College London team has shown that the microstructure of different alloys (i.e. the pattern of crystals inside the alloys) has a direct impact on the performance of a magnetic fridge. This finding could now help the team create the best material required for the system to succeed.
Unlike the main body of research being conducted across the globe on magnetic refrigeration, the focus for the Imperial team is less about analysing and testing large samples of materials, and more about 'understanding the microstructure of these materials and how they respond to magnetic fields on a microscopic level,' says Imperial College London's Professor Lesley Cohen.
'We found that the structure of crystals in different metals directly affects how dramatically they heat up and cool down when a magnetic field is applied and removed,' she explains.
'This is an exciting discovery because it means we may one day be able to tailor-make a material from the "bottom up", starting with the microstructure, so it ticks all the boxes required to run a magnetic fridge. This is vitally important because finding a low-energy alternative to the fridges and air-conditioning systems in our homes and workplaces is vital for cutting our carbon emissions and tackling climate change.'
Source: Cordis
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