Cobalt Generates A Magnetic Polymer

By incorporating a monomer with a cobalt ligand into a block copolymer, researchers have produced a magnetic material that could vastly increase the density of information storage. Gregory N. Tew, professor of polymer science and engineering at the University of Massachusetts, Amherst, reported the material on Aug. 17 at the ACS national meeting in Washington, D.C.

By contrast, Tew said, a homopolymer formed solely from the cobalt-containing monomer is not magnetic.

"As far as I know, this is the first report of a processible, ferromagnetic polymer which is prepared at room temperature and is magnetic at room temperature," commented University of Bristol chemistry professor Ian Manners, who has studied metal-containing polymers for almost 20 years.

The block copolymer is formed from two types of oxanorbornene monomers. One has an alkyl side chain; the other has an acetylene side chain complexed with dicobalt hexacarbonyl. The researchers used ring-opening metathesis to form the copolymer and then evaporated the carbonyl ligands to generate cobalt particles within the material.

The two types of blocks in the resulting polymer are immiscible and try to separate, but they can't move far because the blocks are covalently tethered together. These interactions form nanosized cylinders containing the cobalt. Tew believes that confinement of the cobalt within these cylinders gives the copolymer its magnetic properties. Conversely, the homopolymer is not magnetic because it forms an amorphous material that lacks the copolymer's nanostructure.

In a transmission electron micrograph of the polymer, the cobalt cylinders look like black dots, which would serve as the basis for data storage. A bit of data could be recorded in each dot by aligning its spin up or down with respect to a magnetic field—assuming a suitably tiny data-recording head could be designed. In that case, Tew told C&EN, "you would be talking about terabytes of data storage per square inch instead of the gigabytes" that can be stored in currently available media.

One advantage of the technique is that it isn't limited to one set of starting materials. "We think that what we're doing could be applied to other monomers, as long as you get the nanostructure right," said Tew, who carried out the research with graduate students Yongping Zha and Rag Maddikeri.