Understanding Spin Transport in Thermoelectric Equipment

Thermoelectric materials will allow the efficient conversion of industrial heat waste into electricity. But to create effective thermoelectric materials, their basic physics must be well understood. Loan: Macrovector on Freepik

Scientists shed light on how the magnetic properties of 2D layers can increase the effects of rotation accumulation on thermoelectric heterostructures.

Rotating thermoelectric materials are an active research area due to their potential applications in thermal energy harvesters. However, the physics underlying the effects of layers between these materials on rotational transport phenomena is unclear. In a recent study, scientists from Chung-Ang University, Korea, shed light on the subject using a newly developed platform to measure the effect of Seebeck rotation. Their findings pave the way for large-scale thermoelectric materials with enhanced properties.

Thermoelectric materials, which can generate an electrical voltage in the presence of a change in temperature, are currently an intensive research area; Thermoelectric energy harvesting technology is among our best shots in greatly reducing fossil fuel use and helping to prevent an worldwide energy crisis. However, there are different types of thermoelectric mechanisms, some of which are less understandable, despite recent efforts. A recent study by scientists in Korea aims to fill such a knowledge gap. Read on to find out how!

One of these mechanisms mentioned earlier is the Seebeck rotational effect (SSE), which was discovered in 2008 by a research team led by Professor Eiji Saitoh from the University of Tokyo, Japan. SSE is a phenomenon in which a temperature change between a non-magnetic material and a ferromagnetic creates a flow of rotations. For thermoelectric energy harvesting purposes, the reverse SSE is particularly important. In certain heterostructures, such as the iron-platinum garnet (YIG / Pt), the rotational flow generated by a temperature change is converted into a current with an electric charge, providing a way to generate electricity from the SSE. the reverse.

Since this rotational charge conversion is relatively inefficient in the most popular materials, researchers have attempted to introduce an atomically thin layer of molybdenum disulfide (MoS).2) between layers YIG an Pt. Although this approach has resulted in an improved conversion, the underlying mechanisms behind the role of MS 2D2 layer in rotary transport remains elusive.

To address this knowledge gap, Professor Sang-Kwon Lee of the Department of Physics at Chung-Ang University, Korea, recently led an in-depth study on this topic, which was published in Letter Nano. Various colleagues from Chung-Ang University participated, as well as Professor Saitoh, in an effort to understand the effect of MS 2D2 in the thermoelectric power of YIG / Pt.

For this purpose, scientists prepared two YIG / MoS2Pt samples with different morphologies in MH2 layer, as well as a reference example without MoH2 all They prepared a measuring platform on which a temperature gradient can be applied, a magnetic field applied and the voltage difference caused by the subsequent rotation current monitored. Interestingly, they found that the inverse SSE, and in turn the thermoelectric performance of the entire heterostructure, can be improved or reduced depending on the size and type of MS2 used In particular, using an empty MS2 multilayer between the YIG and Pt layers gave a 60% increase in thermoelectric power compared to YIG / Pt alone.

Through careful theoretical and experimental analysis, the scientists determined that this apparent increase was caused by the promotion of two independent quantum phenomena that, together, constitute the total inverse SSE. These are called the Hall rotation inverse effect, and the Rashba-Edelstein inverse effect, both of which produce a rotational accumulation which then turns into a load current. Furthermore, they investigated how holes and defects in the MoH2 the layer changed the magnetic properties of the heterostructure, leading to a favorable increase of the thermoelectric effect. Enthusiastic about the results, Lee notes: “Our study is the first to prove that the magnetic properties of the interface layer cause fluctuations in rotation at the interface and ultimately increase the accumulation of rotation, leading to a higher voltage and power plant from SSE opposite.”

The results of this work represent an essential part of the enigma of thermoelectric materials technology and may soon have real-world implications, as Lee explains: “Our findings reveal significant opportunities for thermoelectric power harvesters in large intermediate-layer areas. in the YIG / Pt system They also provide essential information for understanding the physics of the combined Rashba – Edelstein and SSE effect in rotational transport. “He adds that their SSE measurement platform can be a great help in investigating types of other quantum transport phenomena, such as the Hall and Nernst effects directed by the valley.

Let’s hope thermoelectric technology advances rapidly in order to make our dreams of a more family-friendly society a reality!

Reference: “Enhanced Spin Seebeck Thermopower in MS / Pt / Holey2/ Y3Fe512 Hybrid Structure ”by Won-Yong Lee, No-Won Park, Gil-Sung Kim, Min-Sung Kang, Jae Won Choi, Kwang-Yong Choi, Ho Won Jang, Eiji Saitoh and Sang-Kwon Lee, December 4, 2020, Letter Nano.
DOI: 10.1021 / acs.nanolett.0c03499

About Chung-Ang University

Chung-Ang University is a comprehensive private research university located in Seoul, South Korea. It started as a kindergarten in 1918 and achieved university status in 1953. It is fully accredited by the Korean Ministry of Education. Chung-Ang University conducts research activities under the motto “Justice and Truth”. His new vision for completing 100 years is the “Global Creative Leader”. Chung-Ang University offers undergraduate, postgraduate and doctoral programs, which include a law school, management program and medical school; there are 16 undergraduate and postgraduate schools each. Chung-Ang University culture and art programs are considered the best in Korea.

About Professor Sang-Kwon Lee

Dr. Sang-Kwon Lee received his PhD in Electronic Engineering from the Royal Institute of Technology, Sweden, in 2002. He was first appointed Assistant Professor in the Department of Semiconductor Science and Technology at Chonbuk National University, Korea, in 2002 and later joined the Department of Physics at Chung-Ang University in 2013 as Professor. He is currently in charge of teaching Modern Physics and Mathematical Physics at Chung-Ang University. His research interests revolve mainly around solid state physics, such as the development and modeling of nanoscale thermoelectric materials and equipment. He works in nanobiotechnology – such as nanobiological semiconductor sensors and the characterization of cancer cells through devices such as nanowires – microfluidics and microelectromechanical systems. Currently, he is also interested in working on valley-related effects, such as the Nernst valley effect, the Hall-valley effect, and various new Seebeck effects for energy harvesting applications in his quantum transport research laboratory at the University. Chung-Ang. He has over 140 publications in his name.

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