Stabilising magnetic materials
Magnetic materials can be made using block copolymers to create nanostructures at low temperatures, say scientists at the University of Massachusetts, USA.
The method could lead to the development of new memory media, such as giant magneto-resistive devices and futuristic spintronic devices. ‘Those devices will continue to shrink in size which mean they need more bits per area,’ explains polymer scientist Greg Tew.
‘All magnetic materials require some level of order, often at the atomic level. This is the first time that small, nonmagnetic particles have been ordered into room temperature magnetic materials.’
The team developed a technique to make ordered magnetic materials based on cobalt nanostructures by encoding a block copolymer with chemical information to self-organise into nanoscopic domains. After synthesising the non-magnetic block copolymer and processing it into a thin film, they found heating once to temperatures of 390°F, converted it into a magnetic film with ordered arrays of small (15 nm) magnetic domains.
According to Tew, another novel aspect is the assembly of the particles. Small cobalt particles are normally too small to be magnetic at room temperature, but the confined geometry of the block copolymers makes them interact and become magnetic at room temperature. ‘Within one block of the copolymer we built in a chemical unit that contained the metal ions with liable ligands,’ says Tew.
‘Upon heating, these ligands evaporate, allowing the metal ions to grow into metal particles. Since the particles are confined to one domain of the block copolymer. It is possible to use the block copolymer ordering to order the magnetic particles over large domains.’
The block’s ability to selforganise into nanoscopic structures one millionth of a millimetre thin, could lead to more industrial applications, says Tew, because the smaller the structures are, the higher their density.
Tew also claims that his method of creating roomtemperature ferromagnetic materials is more efficient and stable than existing methods, though he adds that there is no particular traditional method for this process, as ‘previous approaches (such as film casting or UV light), either fail to confine the particles, do not generate magnetic materials, or require multiple processing steps’. This route he claims would offer a more energy efficient route.