Oak Ridge boffins twist exotic metal into eco-friendly, solid-state cooler

Chill out, no fridge required

The US Department of Energy's Oak Ridge National Laboratory (ORNL) has been investigating exotic materials in pursuit of solid-state cooling devices without needing refrigerants or moving parts.

The findings, published in the journal Science Advances, hold out the promise of enhancing materials to enable more environmentally friendly ways of cooling things, from food to vehicles to electronics, with a quiet, compact and lightweight system that allows precise temperature control.

One material in question, a nickel-cobalt-manganese-indium magnetic shape-memory alloy (try saying that three times quickly) can be deformed then returned to its original shape by forcing it through a phase transition, either by increasing temperature or by applying a magnetic field, according to ORNL.

When a magnetic field is used, the material undergoes a magnetic and structural phase transition, during which it absorbs and releases heat, a behavior known as the magnetocaloric effect.

This effect could be harnessed to provide refrigeration, the researchers claim, which is why the material is considered to be a prime candidate for use in solid-state cooling.

In their investigations, the researchers performed neutron scattering measurements of the magnetic field and temperature dependence of the phonons and magnons in the material, which has the formulation Ni45Co5Mn36.6In13.4.

Phonons and magnons are quasiparticles, with phonons representing an excited state in the quantization of the modes of vibrations, while magnons are described as thermally excited spin waves that reduce the internal magnetization of magnetic materials by creating spin misalignment.

According to ORNL, these quasiparticles "couple in a synchronized dance" in small regions across the disordered arrangement of atoms that make up the material, and patterns of behavior in these regions have important implications for the thermal properties of the material.

These localized hybrid magnon-phonon modes were found to modify the material's phase stability, which results in alterations in the material's properties and behavior that can be tuned and tailored.

Quoted on Phys.org, Michael Manley, leader of the ORNL study, said that their investigations found that the cooling capacity of the material is tripled by the heat contained within those local magnon-phonon hybrid modes, and these findings should lead to better materials for solid-state cooling applications.

This would likely involve controlling a magnetic shape-memory alloy such as this so that it can be used as a heat sponge for efficient cooling without the need for traditional refrigerants or mechanical components.

Last year, a company called Frore Systems introduced its own take on solid-state cooling. Its AirJet technology uses tiny membranes that vibrate at ultrasonic frequency to generate a flow of air that removes heat from a heat spreader inside the device.

Frore's AirJet Mini implementation was used in a mini PC from Zotac Technology, the ZBOX pico PI430AJ, which used it to cool its Intel Core i3 processor. ®

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