Light activates magnetic plastic

17 Jun 2002

US researchers have, for the first time, developed a light-tunable magnetic plastic.

Magnetic plastic

A team of US researchers from the universities of Ohio State and Utah has developed the first magnetic plastic whose magnetism is tuned by light. The plastic becomes 1.5 times more magnetic when blue light shines on it while green light partially reverses the effect (Phys. Rev. Lett 88 057202).

Other groups have investigated plastic or light-responsive magnets but until now, a successful merger of the two at high temperatures, equivalent to those of modern superconductors, has been elusive.

The team developed the magnet by combining an organic material called tetracyanoethanide (TCNE) with manganese ions. Lead researcher, Arthur Epstein, based at the Center for Materials Reasearch, Ohio, told Optics.org: "TCNE interacts well with metal ions, giving the opportunity to use organic chemistry to design desirable magnetic and processing properties."

To induce maximum magnetization, the researchers illuminated the material for 6 hours at 50 mW/cm² using an argon-ion laser operating in continuous wave on the blue 488 nm line. They claim that these effects can persist for up to 11 days.

The photoinduced magnetization can be reduced in two ways: by either heating the material to temperatures above 250 K, which rapidly erases the magnetization or illuminating the sample with the green 514 nm argon-ion line. This reduces the magnetization to 60 % of its maximum value.

Epstein and his co-workers believe that the blue and green light causes the molecules to change shape which in turn affects the magnetic properties. They also claim that during magnetization of the plastic, electrons are forced into a metastable state. Because of this electronic transition, the plastic remains magnetized even when the light is removed.

At present, the magnet functions up to a temperature of 75 K. Epstein explained however that the next research goals "are to raise the operating temperature closer to room temperature; increase the temperature for photoinduced magnetism; and gain greater control of the color of light that produces the changes".

Although commercial production is several years away, Epstein believes that possible applications for such a magnet include writing and erasing data from computer hard-drives, smart cards and remote control of magnetism.