Gadolinium smart cord contains particles of gadolinium embedded in a polythene extrusion, which also contains a thermochromic dye as a useful visual marker of the transition point. If the (normally red) cord is floated on cold water it will jump up and adhere to a small neodymium magnet. If floated on hot water the cord loses its colour and is no longer susceptible to magnetic attraction - i.e. when the cord is red the embedded gadolinium is ferromagnetic and when colourless paramagnetic.
Gadolinium is an important member of the ‘rare earth’ (lanthanides) group of elements. It has an exceptionally low Curie point – the threshold at which a material changes from ferromagnetic (attracted to a magnet) to paramagnetic (not attracted). The Curie point for gadolinium is approximately 20°C, which makes it ideal as a contrast agent (gadopentetate dimeglumine) for MRI scans – showing where the blood is. Gadolinium is also used to regulate neutron activity in nuclear reactors and may be alloyed with other rare earths for applications such as magnetic recording heads.
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