Rare earth compounds could be used in environmentally-friendly magnetic refrigerators, according to a leading US scientist. 

Gordon Miller at Iowa State University and the US Department of Energy's Ames Laboratory claims that materials made from rare earth elements, such as gadolinium, together with the Group 14 tetrelide elements silicon and germanium, could be used to make solid-state magnetic refrigerators with higher cooling efficiencies than conventional refrigerators. 

The cooling effect of these materials is due to the magnetocaloric effect (MCE). This is the tendency of some materials to produce heat when they are placed in a magnetic field, and to cool down when they are removed from this field. The discovery that compounds related to Gd₅Si₂Ge₂ have extraordinarily strong magnetocaloric responses has raised hopes that they might replace conventional refrigeration technology in the near future, said Miller. 

Conventional refrigerators use coolants which have in the past included toxic gases and greenhouse gases that can leak out of the device. Magnetic refrigeration doesn't use any harmful gases, so is claimed to be more environmentally-friendly. 

Miller cautions that any study into the behaviour of rare earth tetrelides requires the careful synthesis of samples that are free from impurities. 'Commercially available rare earth elements contain impurity levels that are sufficiently high to impede the magnitude of the MCE,' said Miller.

Ekkes Brück, a physicist at the University of Amsterdam, the Netherlands, agrees with Miller. 'I think that the main obstacle for application of rare earth tetrelide materials is the extreme sensitivity of the magnetocaloric effect on impurities and the restriction to sub room-temperature,' said Brück. 

Caroline Moore