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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.