By Josh Perry, Editor
[email protected]

Researchers from the National Institute for Materials Science (NIMS) and Tohoku University (Japan) have observed the anisotropic magneto-Peltier effect, a thermoelectric conversion phenomenon in which redirection of a charge current in magnetic material induces heating and cooling.

Experimental configuration for measuring the anisotropic magneto-Peltier effect and lock-in thermal images of a U-shaped ferromagnet. (NIMS)

According to an announcement from NIMS, the joint study developed a novel thermal control function using magnetic material without a junction structure.

“The NIMS-led research team used a thermal measurement technique called lock-in thermography to make systematic measurements of temperature changes in a magnetic material while a charge current was applied,” the announcement explained. “As a result, [researchers] observed changes in the Peltier coefficient in relation to the angle between the direction of the charge current and the direction of the magnetization in the magnetic material.”

This was the first time that this type of observation was possible and researchers hope that it will continue to advance the understanding of thermoelectric conversion.

The article added, “Application of the anisotropic magneto-Peltier effect may enable thermoelectric temperature control of a magnetic material by simply redirecting a charge current in the material and creating a non-uniform magnetization configuration within it, rather than forming a junction between two different electrical conductors.”

The research was recently published in Nature. The abstract stated:

“The Peltier effect, discovered in 1834, converts a charge current into a heat current in a conductor, and its performance is described by the Peltier coefficient, which is defined as the ratio of the generated heat current to the applied charge current. To exploit the Peltier effect for thermoelectric cooling or heating, junctions of two conductors with different Peltier coefficients have been believed to be indispensable.

“Here we challenge this conventional wisdom by demonstrating Peltier cooling and heating in a single material without junctions. This is realized through an anisotropic magneto-Peltier effect in which the Peltier coefficient depends on the angle between the directions of a charge current and magnetization in a ferromagnet. By using active thermography techniques, we observe the temperature change induced by this effect in a plain nickel slab.

“We find that the thermoelectric properties of the ferromagnet can be redesigned simply by changing the configurations of the charge current and magnetization, for instance, by shaping the ferromagnet so that the current must flow around a curve. Our experimental results demonstrate the suitability of nickel for the anisotropic magneto-Peltier effect and the importance of spin–orbit interaction in its mechanism.

“The anisotropic magneto-Peltier effect observed here is the missing thermoelectric phenomenon in ferromagnetic materials—the Onsager reciprocal of the anisotropic magneto-Seebeck effect previously observed in ferromagnets—and its simplicity might prove useful in developing thermal management technologies for electronic and spintronic devices.”