A research team from the National Institute for Materials Science (NIMS) and the University of Tokyo (UTokyo) has recently made a significant breakthrough in the field of magneto-thermoelectric conversion, which has the potential to revolutionize energy harvesting and cooling technologies. This breakthrough, published in the journal Nature Communications, proposes a new method for enhancing the transverse magneto-thermoelectric effect in magnetic materials, showing that performance can be significantly improved by creating artificial materials that consist of obliquely stacked multilayers of magnetic metals and semiconductors.
Magneto-thermoelectric conversion refers to the generation of an electric current in response to both a magnetic field and a temperature gradient. In particular, the transverse magneto-thermoelectric effect, known as the anomalous Nernst effect (ANE), is a phenomenon in which a charge current is induced in a direction that is perpendicular to both the temperature gradient and the magnetization of the material. This phenomenon has attracted significant attention in recent years for its potential applications in thermoelectric devices, which can convert waste heat into electricity or provide cooling.
The research team’s study focuses on enhancing the performance of ANE for practical thermoelectric applications. The ANE has long been considered a promising approach due to its potential for versatile, durable, and low-cost thermoelectric materials. However, despite ongoing research, a material has yet to be discovered that achieves the high performance needed for practical thermoelectric devices at room temperature. The current best-performing material for ANE is a cobalt-based topological magnet, Co2MnGa, discovered in 2018. However, even this material falls short of the performance required for real-world applications, with improvements needed by more than 100 times.
To address this challenge, the team developed a novel approach involving artificially engineered multilayers. By stacking layers of magnetic metals and semiconductors at an oblique angle, the researchers were able to create a material that exhibits both the off-diagonal Seebeck effect (ODSE) and ANE simultaneously. The ODSE is a thermoelectric phenomenon in which a temperature gradient produces a charge current that is orthogonal to both the temperature gradient and the electric field in the material. The key innovation of the research is that this transverse thermoelectric conversion can occur without the need for an external magnetic field or magnetization. This discovery represents a significant advancement, as it opens up the possibility of creating efficient thermoelectric devices that do not rely on external magnetic influences.
The team’s results demonstrated that this artificially tilted multilayer structure could increase the dimensionless figure of merit for ANE by more than an order of magnitude compared to using a single magnetic metal alone. This improvement is attributed to the synergistic effect of the combined ANE and ODSE, which work together to enhance the overall thermoelectric performance. This finding suggests that certain physical parameters and material structures, which had not been the focus of previous research on ANE, play a crucial role in improving the efficiency of transverse thermoelectric conversion.
The implications of this research are significant. It provides new insights into the design of materials for transverse thermoelectric conversion, particularly through the structural engineering of multilayer materials. The study also suggests that the properties of the materials themselves, including their physical structure, play a key role in improving performance. This new perspective opens up possibilities for designing more efficient materials for energy harvesting, particularly for applications that involve waste heat recovery, electronic cooling, and heat sensing technologies.
The research team now aims to further develop these artificial materials to achieve even higher thermoelectric performance, with the goal of making them viable for practical applications. By applying these findings, it may be possible to create highly efficient thermoelectric materials that can harness waste heat from industrial processes, automotive engines, or even household appliances, turning it into usable electricity. Furthermore, the materials could be used in cooling technologies, providing more energy-efficient solutions for electronics and other devices that generate heat.