New class of swelling magnets – sciencedaily

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A new class of magnets, which increase their volume when placed in a magnetic field and generate negligible amounts of unnecessary heat during energy harvesting, has been discovered by researchers at Temple University and the University. from 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 21 issue of the journal, Nature (DOI: 10.1038 / nature14459).

This transformative breakthrough has the potential not only to displace existing technologies, but also to create whole 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 directs the Materials Genomics and Quantum Device Labs at Temple’s College of Engineering.

In the 1840s, physicist James Prescott Joule discovered that iron-based magnetic materials changed shape but not volume when placed in a magnetic field. This phenomenon is called “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’, which show a large volume change in magnetic fields,” Chopra said. “In addition, these non-Joulian magnets also possess the remarkable ability to harvest or convert energy with minimal heat loss.”

“The response of these magnets is fundamentally different from that probably envisioned by Joule,” Wuttig said. “He must have thought that the magnets react uniformly.”

Chopra and Wuttig found that when they heat-treated certain iron-based alloys by heating them in an oven to around 760 degrees Celsius for 30 minutes, then rapidly cooling them to room temperature, the materials exhibited non-Joulian behavior.

The researchers found that the heat-treated materials contained microscopic cell-like structures never seen before, whose response to a magnetic field is at the heart of non-Joulian magnetostriction. “Knowing about this unique structure will allow researchers to develop new materials with equally attractive properties,” Wuttig added.

The researchers noted that conventional magnets can only be used as actuators to exert forces in one direction because they are limited by Joule magnetostriction. Actuation, even in both 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 made, they said.

Because these new magnets also have energy efficiency characteristics, they can be used to create a new generation of sensors and actuators with extremely low thermal signatures, the researchers said. These magnets could also find applications in efficient energy recovery devices; compact microactuators for aerospace, automotive, biomedical, space and robotics applications; and ultra-low thermal signature actuators for sonar and defense applications.

Since these new magnets are made from alloys free of rare earth elements, they could replace existing rare earth-based magnetostriction alloys, which are expensive and have inferior mechanical properties, the researchers said.

“The work of Chopra and Wuttig is a good example of how advances in basic research can be a game-changer,” said Tomasz Durakiewicz, director of the condensed matter physics program at the National Science Foundation. “Their search for generally accepted principles on magnetism led to a new understanding of an old paradigm. This research has the potential to catapult sustainable and energy efficient materials into a very wide range of applications. “

The research was supported by the Condensed Matter Physics and Metals programs of the Division of Materials Research of the National Science Foundation.


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