August 6, 2015

Non-magnetic metals turned into magnets

Maurice Savage/Alamy
Copper: not a magnetic metal, unless it is combined in thin films with organic molecules.

Thin films of copper and manganese made to behave like iron, cobalt or nickel.

(August 6, 2015)  Two common metals that are not magnetic — copper and manganese — can be transformed into magnets: a surprising effect that involves combining thin films of the metals with carbon-based organic molecules.

The magnetism is weak and fades away after a few days, but the discovery could lead to new kinds of hybrid metal–organic magnets that might be useful in applications such as medical imaging, says Oscar Cespedes of the University of Leeds, UK, who led the work1 reported on 5 August in Nature.

Permanent magnets, such as iron bars, gain their pulling power from the spins of the electrons inside them. This quantum-mechanical property means that each electron generates its own magnetic field. Most electrons couple their spins so as to cancel each other out, producing no overall effect, but some ‘unpaired’ electrons will align with an external magnetic field, and will stay that way when that field is removed. The cumulative effect of these tiny aligned magnetic fields makes the metals iron, cobalt and nickel magnetic at room temperature.

Cespedes and his colleagues made copper and manganese behave this way, too. They laid down films of the metals on layers of buckyballs, which are cage-like molecules made up of 60 carbon atoms, chosen because they are particularly good at stripping electrons from the metal films. This made the films partially magnetic, across a layer a few nanometres thick next to the buckyballs. When an external field was applied and then removed, some 10% of the induced magnetic field remained, producing a weak magnet.

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