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Impossible Efficiency: Magnets and Heat Recovery

A study published in the journal ‘Science Advances’ has demonstrated a new way of converting heat into electricity. This technology could improve the efficiency of some industrial processes and save on greenhouse gas emissions. The study, which was carried out by researchers at Ohio State University, showed that objects called ‘paramagnets’ can be used to harvest electricity from heat, a process which was previously thought to be impossible. 

Electricity and magnetism are very closely linked. If you place a compass beside a live electrical wire, you will see the needle shift. This is because the movement of electrons generates a magnetic field. Similarly, if you pass a magnet along a wire, you will generate a current. This is because the spin waves generated by the magnets, also called magnons, drag the electrons through the wire. This effect can be used to generate electricity from heat in a process known as ‘magnon drag thermopower’. 

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When you heat a magnet to a certain temperature, the material loses its long-range magnetic properties and becomes what is known as a ‘paramagnet’. Until this research surfaced, it was thought that the spin waves of paramagnets (also known as paramagnons) did not ‘correlate’ for long enough to be used for thermopower. What the researchers found was that paramagnons require only 1 femtosecond (one quadrillionth of a second) of correlation to generate a current. 

What this means in practice is that paramagnons can be used to generate electricity from heat in a wide range of situations. One such application could be found in ‘smart clothes’, in which the energy required to power the clothes could be harvested from the user’s body heat. A more commonplace example is that the heat coming out of car exhausts could be used to recharge the car’s battery. This would improve fuel efficiency, saving money for drivers and lessening the impact of cars on the environment.

 

Adam Boland – Science Editor

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