Record-breaking, fast-spinning magnet could help uncover new physics

Magnets can be made to levitate by the Meissner effectScience History Images / Alamy A tiny magnet that levitates within a superconductor trap may be the fastest spinning object visible to the naked eye, and one of the fastest spinning objects ever made. In the future, it could be used in experiments searching for mysterious dark matter particles and aid the development of quantum technologies. Superconductors are materials that conduct electricity with perfect efficiency, and they also expel any magnetic field that tries to permeate them – a phenomenon known as the Meissner effect. Because of this, a magnet placed above a superconductor experiences repulsive magnetic forces and starts to levitate. Tao Wang at the Agency for Science Technology and Research in Singapore and his colleagues have now set one such levitating magnet spinning at an unprecedently fast rate. Read more A miniature magnet rivals behemoths in strength for the first time The researchers used a spherical magnet made from neodymium, iron and boron that was about 30 micrometres wide, similar to the width of a fine human hair. They placed it in a cylindrical container made from lead, then enclosed that container in a chamber devoid of air, or a vacuum chamber. Advertisement if( window?.adverts?.addToArray ) { window.adverts.addToArray( { "pos": "mid-article-slot" } ); } Next, they used liquid helium to cool the whole setup to approximately -269°C (-452°F), only a few degrees above the coldest possible temperature. Under these extreme circumstances, lead behaved as a superconductor and the lack of air meant that the magnet could levitate within it without bumping into any particles. The team set the magnet spinning with a magnetic coil, ultimately pushing this tiny rotor to 138 million revolutions per minute. Wang says the magnet’s spinning was also very stable: it would take 17 days for its spinning speed to decrease by 50 per cent, something that would typically happen more quickly due to interactions between the magnet and its environment. “In terms of how many turns it makes before slowing down significantly, this is in the same league as the Earth’s spinning,” he says. “This, so far, is the fastest magnetically levitated rotor.” The record for the fastest rotating human-made object is also held by a levitated sphere, but that one was nano-sized, so invisible to the naked eye, and levitated by laser beams. Read more Physics of light and magnetism rewritten after almost two centuries Because the rotor experiences essentially no friction, and it is magnetic and cold, its behaviour is very sensitive to its environment, which makes it a promising sensor. The team has already successfully tested it as a gauge of vacuum at very low temperatures. Wang says this could be useful for builders of quantum computers, which often must be kept extremely cold and isolated in order to work. Benjamin Stickler at Ulm University in Germany says the levitated spinning magnet could also be used to precisely sense and measure magnetic fields. It could also be a promising platform for tests of fundamental physics, such as looking for effects related to dark matter particles, or sensing gravitational waves at so far unexplored frequencies, says team member Andrea Vinante at the National Research Council in Italy. Additionally, at very low temperatures quantum effects become dominant, so it could even be used for explorations of quantum mechanics and its interplay with gravity at micrometre scales, he says. Journal Reference: Science Advances DOI: 10.1126/sciadv.aee6434