Researchers at Temple University and the University of Maryland has discovered 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.

The researchers, Harsh Deep Chopra, professor and chair of mechanical engineering at Temple, and Manfred Wuttig, professor of materials science and engineering at Maryland, have published their findings, “Non-Joulian Magnetostriction,” in the journal Nature.

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.

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.

Never before seen highly periodic magnetic ‘cells’ or ‘domains’ in iron-gallium alloys responsible for non-Joulian magnetism.  Image Credit:Harsh Deep Chopra at Temple University.  Click image for the largest view.

Never before seen highly periodic magnetic ‘cells’ or ‘domains’ in iron-gallium alloys responsible for non-Joulian magnetism. Image Credit:Harsh Deep Chopra at Temple University. Click image for the largest view.

Chopra, who also runs the Materials Genomics and Quantum Devices Laboratories at Temple’s College of Engineering, said, “Our findings fundamentally change the way we think about a certain type of magnetism that has been in place since 1841. We have discovered a new class of magnets, which we call ‘Non-Joulian Magnets,’ that show a large volume change in magnetic fields. Moreover, these non-Joulian magnets also possess the remarkable ability to harvest or convert energy with minimal heat loss.”

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

Chopra and Wuttig made the discovery when they thermally treated certain iron-based alloys by heating them in a furnace at approximately 760º C for 30 minutes, then rapidly cooled them to room temperature, the materials then 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 explained.

The researchers noted that conventional magnets can only be used as actuators for exerting forces in one direction since they are limited by Joule magnetostriction. Actuation, even in two directions, requires bulky stacks of magnets, which increase size and reduce efficiency. Since non-Joulian magnets spontaneously expand in all directions, compact omnidirectional actuators can now be easily realized.

Because these new magnets also have energy efficient characteristics, they can be used to create a new generation of sensors and actuators with vanishingly small heat signatures. The magnets could also find applications in efficient energy harvesting devices; compact micro-actuators for aerospace, automobile, biomedical, space and robotics applications; and ultra-low thermal signature actuators for sonars and defense applications.

Also of great interest is the new magnets are composed of alloys that are free of rare-earth elements, they could replace existing rare-earth based magnetostriction alloys, which are expensive and feature inferior mechanical properties.

Tomasz Durakiewicz, National Science Foundation condensed matter physics program director said of the work, “Chopra and Wuttig’s work is a good example of how basic research advances can be true game changers. Their probing of generally accepted tenets about magnetism has led to a new understanding of an old paradigm. This research has the potential to catapult sustainable, energy-efficient materials in a very wide range of applications.”

This research is quite interesting in that the new results have great potential. But the potential is yet to even be realized because the research is so very basic.

Yet the 175 year old assumption has been turned upside down, or is it inside out or doubled up? Whatever the description there will be some confirmations, fails and naysayers. But this discovery is important, with implications that today can only be imagined.


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