Magnets boost pulling power

Researchers at Trinity College Dublin are in the forefront of research into a new generation of permanent magnets which include rare earth elements.

These "rare earth magnets" are far more powerful than the ferric permanent magnets familiar to generations of children who experimented with horse-shoe shaped versions. Even the best ferric permanent magnets can't compete with those made with a combination of the rare earth neodymium, iron and boron.

New developments and the potential markets for these magnets are discussed in a report by Prof Michael Coey and Prof Denis Weaire of Trinity in the current issue of the leading US journal, the Industrial Physicist, published by the American Institute of Physics. These magnets can be formed into any shape without losing their magnetic strength. Groups of permanent magnets can also be assembled so that complex magnetic fields can be achieved.

These new materials have been under study at Trinity for over 10 years, explained Prof Weaire. "Research continues to optimise the choice of chemical compound and its processing." The team effort involves 15 including postgraduate and post-doctoral students and contributions from visiting experts from abroad.

Strong international links in permanent magnet research were formed some years ago when Prof Coey was the European co-ordinator for the Community's "Concerted Action on Magnetism", a research initiative which involved 57 member-state labs.

ONE new development from the Trinity group is a rare earth compound which allows a much higher Curie Point, the temperature at which heat causes a loss of magnetism. The neodymium-based compounds tend to have a Curie Point of about 312 Celsius but a compound based on samarium with iron and nitrogen has shown greater heat resistance with a Curie Point of 477 Celsius, Prof Weaire said.

This would allow their use in applications where a magnetic field is required in a high- temperature environment. The new more powerful permanent magnets are a substitute for electromagnets and have the advantage of not needing the wiring, electricity or the cooling systems needed by very strong electromagnets.

They are also in widespread use in smaller applications. They are used in hard disk drive read heads and the current annual disk drive production of 300 million units is expected to grow to one billion by 2002.