A miniature magnet rivals behemoths in strength for the first time

A magnet small enough to fit in the palm of your hand can match the strength of some of the world’s most powerful magnets for the first time.

Strong magnets play many roles across science and technology, with uses in everything from MRI imaging and particle accelerators to nuclear fusion efforts. The most powerful among them are made from superconductors, materials that conduct electricity with near-perfect efficiency.

But superconducting magnets that produce strong magnetic fields are often bulky: smaller ones are typically the same size as the Star Wars robot R2D2, while the largest are comparable to a two-storey building, says Alexander Barnes at ETH Zurich in Switzerland.

He and his colleagues have now built a superconducting magnet that is competitive with those large magnets in strength, but measures only 3.1 millimetres in diameter. They made it by coiling a thin tape of a ceramic material called REBCO, which superconducts when cooled to extremely low temperatures. These coils produce magnetic fields when electric currents are passed through them.

The team bought the REBCO tape from a commercial company, then set out to find the best magnet design, which involved making and testing over 150 of them, says Barnes. “Our strategy was to develop and embrace a ‘fail often and fail fast’ approach.”

They ultimately settled on a design that involves either two or four pancake-shaped coils of REBCO that could produce magnetic fields with strengths of 38 Tesla and 42 Tesla, respectively. For comparison, a fridge magnet typically has a magnetic field strength under 0.01 Tesla. The two magnets that currently produce the world’s strongest steady magnetic fields reach around 45 Tesla, weigh many tonnes and require up to 30 megawatts of power. Barnes and his team’s magnet is smaller than your hand and requires less than 1 watt of power.

Barnes says their ultimate goal is to use this magnet for nuclear magnetic resonance (NMR), an experimental technique that uses magnetic fields to reveal the structure of molecules such as drugs and catalysts for industrial processes. In his view, this powerful technique is stymied by how big and expensive magnets are, but the researchers hope to make it accessible for more chemists. The team has already begun testing the magnet in an NMR setup, says Barnes.

“Producing magnetic fields above 40 Tesla traditionally requires very large and expensive facilities, so achieving similar field strengths in such a compact device using superconducting tapes is significant,” says Mark Ainslie at King’s College London. “It suggests that extremely high-field magnets could become more accessible to a wider range of laboratories in the near future.”

But questions remain before the magnet can achieve widespread use – for instance, how uniform the magnetic field can be made and how the electromagnetic behaviour of these coils can be managed and controlled, he says.