A new class of magnets that expand their volume when placed in a magnetic field and generate negligible amounts of wasteful heat during energy harvesting, has been discovered by researchers at Temple University and the University of Maryland. The researchers, Harsh Deep Chopra, professor and chair of mechanical engineering at Temple, and Manfred Wuttig, professor of materials science and engineering at Maryland, published their findings, "Non-Joulian Magnetostriction," in the May 21st issue of the journal, Nature (DOI:10.1038/nature14459).

This transformative breakthrough has the potential to not only displace existing technologies but create altogether new applications due to the unusual combination of magnetic properties.

"Our findings fundamentally change the way we think about a certain type of magnetism that has been in place since 1841," said Chopra, who also runs the Materials Genomics and Quantum Devices Laboratories at Temple's College of Engineering.

In the 1840s, physicist James Prescott Joule discovered that iron-based magnetic materials changed their shape but not their volume when placed in a magnetic field. This phenomenon is referred to as "Joule Magnetostriction," and since its discovery 175 years ago, all magnets have been characterized on this basis.

"We have discovered a new class of magnets, which we call 'Non-Joulian Magnets,' that show a large volume change in magnetic fields," said Chopra. "Moreover, these non-Joulian magnets also possess the remarkable ability to harvest or convert energy with minimal heat loss."

"The response of these magnets differs fundamentally from that likely envisioned by Joule," said Wuttig. "He must have thought that magnets respond in a uniform fashion."

Chopra and Wuttig discovered that when they thermally treated certain iron-based alloys by heating them in a furnace at approximately 760 degrees Celsius for 30 minutes, then rapidly cooled them to room temperature, the materials exhibited the non-Joulian behavior.

The researchers found the thermally treated materials contained never before seen microscopic cellular-like structures whose response to a magnetic field is at the heart of non-Joulian magnetostriction. "Knowing about this unique structure will enable researchers to develop new materials with similarly attractive properties," Wuttig added.