Magnetism in a spin

Funny old thing magnetism, just when you think you understand what it is and what it can do something new comes along. A Trinity College Dublin physicist has used it to levitate non-magnetic materials and to stop two liquids in a single container from mixing.

Professor of experimental physics in Trinity’s School of Physics, Michael Coey is used to being surprised by magnetism and magnetic materials, having studied them for much of his professional research career.

Advanced magnetic materials have allowed us to pack 100 billion bits of computer information on a single square inch of computer storage space. They also look likely to produce the next generation of computers, systems that won’t have to be reloaded with software every time you switch them on.

Coey is a leading international expert in magnetism and new magnetic materials. He is ranked 309th in a list of the 1,100 most-cited physicists in the world, the only person working in Ireland to appear on this list. He is a foreign associate of the National Academy of Sciences in the US, and a Fellow of the Royal Society. He won the Royal Irish Academy’s inaugural Gold Medal in the Physical and Mathematical Sciences last year, but Coey is also a leading light in the development of a multi-purpose public science gallery in the new building that will house Trinity’s new CRANN nanoscience research laboratories.

In recent years, Coey and his Science Foundation Ireland funded research group have focused their efforts on “nanoscale magnetics and spin electronics”, he explains. “The broad question is what goes funny or what is different if we reduce our magnets to the 10 nanometre range.” A magnet that size is almost impossible to imagine. A human hair is 8,000 times thicker, says Coey.

And yet all modern computer magnetic memory is based on nanoscale magnetics, he says. It relies on magnetism and the building up of layers of thin films, some conductors, some insulators and some magnetic. “It is quite astonishing that people are able to make these films one nanometre (one billionth of a metre) thick on a piece of wafer as big as an old record.”

Spin electronics involves using the smallest natural magnets available—electrons. “The idea of spin electronics is that up to now we only made use of the electron’s negative charge, while ignoring the fact that the electron is in itself a little magnet,” Coey explains. “The big idea with spin electronics is to use the idea that the electron is a little magnet and see what we can do with it.”

The approach is based on a phenomenon first seen in a French lab in 1988 but which, within a decade, had brought about the first generation of nanomagnets and spin electronics.

Coey’s group studies new types of nanofilms using unusual combinations to create novel magnetic effects. “The concept is really very simple. The heart of the device is a sandwich with some magnetic layers and some space,” he explains. “But it has to be built on such a tiny scale.” The team’s particular strength is its long experience with novel magnetic materials, something which informs what new combinations to try.

He believes that this technology will become at least as important to computing as semiconductors. The real breakthrough will come when second-generation nanomagnetic materials actually replace existing semiconductors to allow the production of magnetic transistors. “What would be wonderful is if we had a magnetic semiconductor that could make spin transistors,” he says.

His group has already developed unusual new magnetic materials using combinations that should not really be magnetic at all. “We are very interested in a new group of materials which, to everybody’s surprise, were ordinary oxides that when doped with ferromagnetic material become magnetic at high temperatures. We don’t understand why the magnetic interactions are so strong.”

Meanwhile, the group continues to study novel things about magnetic fields, for example that you can make non-magnetic materials “levitate” in a magnetic field when immersed in paramagnetic liquids. Coey has also discovered that fields can prevent two liquids in a single container from mixing through convection. He can also use magnetic fields to induce mixing in two liquids, a technique valuable in a research area known as micro fluidics.

He is also looking at the use of magnetic materials linked to biomolecules, which could be used in completely new medical imaging technologies.

26 January 2006
Professor Michael Coey

TCD School of Physics: http://www.tcd.ie/Physics
CRANN (Centre for Research on Adaptive Nanostructures and Nanodevices): http://www.tcd.ie/Physics/Crann/