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International Center for Materials Nanoarchitectonics (WPI-MANA)

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[[Research Highlights Vol.51] Enhanced Thermoelectric Conversion in Magnetic Materials through Spin Fluctuations](https://mdr.nims.go.jp/datasets/09a64462-0758-4dbb-bd16-e4313577f95c)

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2022/03/31 16:26 Enhanced Thermoelectric Conversion in Magnetic Materials through Spin Fluctuations| MANAhttps://www.nims.go.jp/mana/research/highlights/vol51.html 1/3Previous  Index  NextResearch Highlights[Vol. 51]Enhanced Thermoelectric Conversion in Magnetic Materials through SpinFluctuations17 Jul, 2019Figure:(A) Thermopower as a function of temperature of Fe2.2V0.8Al0.6Si0.4. The material ordersferromagnetically at TC = 285 K. Above TC, thermopower shows a remarkable enhancement up to50% from the normal-metal one.(B) Schematic illustration of a strong ferromagnetic metal, where local spin density is uniform andthe net magnetization is stable. Then, thermal energy does not affect to electronic properties.(C) In case of weak ferromagne near the magnetic instability, thermal energy is well absorbed tometals to induce spin fluctuation (thermal fluctuation of local spin density), and is effectivelytransferred to electronic energy. As a result, thermopower is enhanced by spin fluctuation in weakferromagnets.Rather than letting ‘waste’ heat dissipate, it is possible to use it and convert it into electricalenergy. Such thermoelectric conversion is an important technology, especially in today’s context ofalternative energy sources. Yet, achieving high recovery efficiency is difficult. Now, Tsujii Naohito atthe International Center for Materials Nanoarchitectonics, National Institute for Materials Science,Tsukuba, Japan, and colleagues have discovered that certain compounds belonging to the so-calledclass of weak itinerant ferromagnets display enhanced thermoelectric power under certainhttps://www.nims.go.jp/mana/research/highlights/vol50.htmlhttps://www.nims.go.jp/mana/research/highlights/index.htmlhttps://www.nims.go.jp/mana/research/highlights/vol52.html2022/03/31 16:26 Enhanced Thermoelectric Conversion in Magnetic Materials through Spin Fluctuations| MANAhttps://www.nims.go.jp/mana/research/highlights/vol51.html 2/3conditions. The finding, which is explained by a physical effect known as spin fluctuations, is likelyan important step towards the development of practical thermoelectric generation systems.The researchers investigated two iron-containing compounds (Fe2V0.9Cr0.1Al0.9Si0.1 andFe2.2V0.8Al0.6Si0.4). These materials are weak ferromagnets. To quantify the thermoelectric powerof the two compounds, Naohito and colleagues measured their Seebeck coefficients over a widetemperature range. (The Seebeck coefficient is defined as the ratio between the voltage generatedby a temperature difference in a material and the temperature difference itself.)The Seebeck coefficients displayed an unexpected enhancement over a broad temperature rangewith a peak around the materials’ Curie temperature (above which they are no longer permanentmagnets) and extending to above room temperature. The latter is important for potential practicalapplication of the compounds’ enhanced thermoelectric power.The scientists noticed that upon applying a magnetic field, the enhancement is suppressed, whichis a signature of so-called spin fluctuations. This phenomenon is understood as follows. In weakferromagnets, spin polarization is easily damped by absorbing heat energy. Then, spin fluctuation(thermal fluctuation in local spin density) is induced in exchange. This helps itinerant electrons gainextra energy, which causes the enhancement in thermopower. Upon applying magnetic field, onthe other hand, the net magnetization becomes stabilized, but the spin fluctuation is suppressed.Thus the enhancement in thermopower vanished in magnetic field.The researchers estimated that for compounds like the ones they investigated, a Seebeckcoefficient enhancement of about 50% is feasible, which would result in a very high thermoelectricconversion power factor.The scientists conclude that their findings “demonstrate that spin fluctuations in weak itinerantferromagnets have an excellent potential to boost thermoelectric PF [power factors] up topractically useful levels around the room temperature range” and that the result “ is quite uniqueand will add a new aspect of correlating magnetism to the power generation technologies.”Reference“Observation of enhanced thermopower due to spin fluctuation in weak itinerant ferromagnet”Naohito Tsujii, Akinori Nishide, Jun Hayakawa, Takao MoriJournal : Sci. Adv. 5, eaat5935 (2019).DOI : 10.1126/sciadv.aat5935AffiliationsInternational Center for Materials Nanoarchitectonics (WPI-MANA), National Institute for MaterialsScience (NIMS), Namiki 1-1, Tsukuba, Ibaraki 305-0044, JapanContact informationInternational Center for Materials Nanoarchitectonics(WPI-MANA)https://samurai.nims.go.jp/profiles/tsujii_naohito?locale=enhttps://samurai.nims.go.jp/profiles/mori_takao?locale=enhttps://advances.sciencemag.org/content/5/2/eaat59352022/03/31 16:26 Enhanced Thermoelectric Conversion in Magnetic Materials through Spin Fluctuations| MANAhttps://www.nims.go.jp/mana/research/highlights/vol51.html 3/3National Institute for Materials Science1-1 Namiki, Tsukuba, Ibaraki 305-0044 JapanPhone: +81-29-860-4710E-mail: mana-pr[AT]ml.nims.go.jp