In a research breakthrough, scientists from the École Polytechnique Fédérale de Lausanne (Swiss Federal Institute of Technology in Lausanne) in Switzerland claim to have provided the first evidence ever that it is possible to generate a magnetic field by using heat instead of electricity, a phenomenon known as the Magnetic Seebeck effect or “thermomagnetism.”
First observed in the mid-1800s by Thomas Johann Seebeck, the Seebeck effect describes the conversion of temperature differences into electricity. On average, electrons on the hotter side of an electric conductor have more kinetic energy and subsequently move at higher speeds than the electrons on the colder side, the research team explained. This difference causes them to diffuse from the hotter to the colder side, generating an electric field proportional to the temperature gradient along the conductor. The Seebeck effect is primarily used to power space probes and thermoelectric generators, and could be implemented for heat-harvesting in power plants, wrist-watches and microelectronics.
It is believed that in theory, it is also possible to generate a magnetic field using temperature differences across an electrical insulator. Led by Jean-Philippe Ansermet, researchers at EPFL were able to experimentally verify the existence of the Magnetic Seebeck effect using an electrical insulator in place of a conductor. While electrons are able to diffuse freely in an electric conductor when exposed to a temperature gradient, an insulator prevents electrons from flowing.
Instead, researchers found, the temperature difference affected the orientation of electrons’ spin, which can generate a magnetic field under certain conditions perpendicular to the direction of the temperature gradient. The intensity of the thermomagnetic field was also determined to be directly proportional to the temperature gradient along the insulator.
Upon examining the propagation of magnetization waves along an insulating material called YIG (yttrium iron garnet), study co-author Antonio Vetrò found that the direction the magnetic waves propagated along the insulator affected the degree of magnetization loss – a phenomenon called magnetic damping. Vetrò found that when the direction of the waves matched the orientation of the temperature gradient along the YIG, then the magnetization damping was reduced; when they propagated to the opposite direction, magnetic damping increased.
While still at an early stage, the research team believes their discovery could open new options for addressing magnetization damping and have an important impact on solid-state devices, magnetic-tunnel transistors and spintronic devices, which rely on the spin of electrons rather than their charge and movement to transmit a signal.