ASU professor finds new twist to old theory

November 15, 2000

Tempe, AZ, Physics and Astronomy professor Ralph V. Chamberlin has found a new twist to an old theory of magnetism. By using a novel application of thermodynamics, Chamberlin successfully extended the range of the mean-field theory of ferromagnetism to accurately describe the behavior of ferromagnetic materials across a broader range of temperatures.

The mean-field theory of ferromagnetism, created in 1907 by Pierre Weiss, was an important milestone in the development of modern physics. It describes the properties of strongly magnetic materials, such as iron, but had an impact far beyond magnet research.

"Mean-field theory was the first viable model for ferromagnetism. Although its predictions near the transitional temperature have been found to be inaccurate, it remains popular as the most versatile approach for describing many different properties in a wide-range of materials," said Chamberlin.

For the past 30 years, an alternative theory has been used for the behavior near the transition. Chamberlin's groundbreaking research shows that the mean-field theory can be extended down to the transition so there is no need for a separate theory.

The mean-field approach can, in fact, describe the behavior of ferromagnets in this regime, as well as higher temperatures. "This becomes possible by including the effect of small, nanometer-sized clusters in the sample," he says.
The long history of the mean-field theory and the implications of Chamberlin's findings are discussed in an accompanying Nature News and Views article by Tom Giebultowicz of Oregon State University.

The research is published in the November 16, 2000 issue of Nature.

Arizona State University

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