Nanostructure design for high performance thermoelectric materials based on anomalous Nernst effect using metal/semiconductor multilayer
About: This article is published in Applied Physics Express.The article was published on 2021-07-01. It has received 6 citations till now. The article focuses on the topics: Nernst effect & Thermoelectric materials.
Citations
More filters
TL;DR: In this paper, the authors discuss recent advances behind new ways to generate large transverse thermoelectric voltages, such as the spin Seebeck and Nernst effects, as well as Weyl physics.
Abstract: Conversion of thermal to electrical energy has been a subject of intense study for well over two centuries. Despite steady progress throughout the past several decades, solid-state thermoelectric (TE) energy conversion devices remain adequate only for niche applications. One appealing option for circumventing the limits of conventional TE physics is to utilize phenomena where flows of heat and charge are perpendicular, the so-called “transverse” geometry. In this Tutorial, we discuss recent advances behind new ways to generate large transverse thermoelectric voltages, such as the spin Seebeck and Nernst effects, as well as Weyl physics. We provide suggestions for how these mechanisms might be enhanced and implemented into high-efficiency, next generation transverse TE devices. We also discuss best practices for accurate measurement and reporting of transverse thermoelectric material properties, including a case study of a round robin spin Seebeck coefficient measurement.
6 citations
TL;DR: In this paper , the anomalous Nernst coefficient (SANE) of epitaxial Fe4N films on MgO(001), MgAl2O4(MAO), and SrTiO3(STO) substrates grown by molecular beam epitaxy was investigated.
Abstract: Anomalous Nernst effect of epitaxial Fe4N films on MgO(001), MgAl2O4(MAO)(001), and SrTiO3(STO)(001) substrates grown by molecular beam epitaxy was investigated. Moderately large anomalous Nernst coefficients ( SANE) of 1.4 and 1.7 μV/K were obtained in the Fe4N films on the MgO(001) and MAO(001) substrates, respectively, and large anomalous Hall angles (∼0.06) and transverse thermoelectric conductivities [∼1.3 A/(m K)] were derived from the experimental results. On the other hand, a large effective SANE of 2.8 μV/K was obtained in the Fe4N film on the STO(001) substrate. The origin of the enhanced effective SANE is the negatively large Seebeck coefficient ( SSE) in an oxygen deficient STO layer near the surface of the STO substrate. This indicates that it is possible to enhance the effective SANE of ferromagnetic materials by utilizing adjacent materials with large | SSE| such as the oxygen deficient STO layer.
3 citations
TL;DR: In this paper , the anomalous Nernst effect (ANE) in CsCl-type Fe 100− X Rh X (X = 45, 48, 50, 52, 54, 60) with a thickness of 50 nm was studied.
Abstract: Abstract We studied the anomalous Nernst effect (ANE) in CsCl-type Fe 100− X Rh X ( X = 45, 48, 50, 52, 54, 60) with a thickness of 50 nm deposited on a thermally oxidized Si substrate. Samples with X < 48 certainly have a ferromagnetic phase, exhibiting the ANE. The composition dependence of the anomalous Nernst coefficient S y x agreed with the transverse thermoelectric conductivity α y x . ∣ S y x ∣ and ∣ α y x ∣ were maximized at X = 48, which has a ferromagnetic state close to the phase transition state. The maximization of ∣ α y x ∣ at X = 48 can be explained using band structure-based calculations, where ∣ α y x ∣ rapidly increases near the phase transition.
3 citations
TL;DR: In this paper , a review of the physical concepts governing the materials to device performance as well as key challenges for enhancing the thermoelectric (TE) performance is presented, where the role of crystal structure in the form of chemical bonding, crystal symmetry, order disorder and phase transition on charge carrier transport in the material has been explored.
Abstract: The continuous depletion of fossil fuels and the increasing demand for eco-friendly and sustainable energy sources have prompted researchers to look for alternative energy sources. The loss of thermal energy in heat engines (100 °C–350 °C), coal-based thermal plants (150 °C–700 °C), heated water pumping in the geothermal process (150 °C–700 °C), and burning of petrol in the automobiles (150 °C–250 °C) in form of untapped waste-heat can be directly and/or reversibly converted into usable electricity by means of charge carriers (electrons or holes) as moving fluids using thermoelectric (TE) technology, which works based on typical Seebeck effect. The enhancement in TE conversion efficiency has been a key challenge because of the coupled relation between thermal and electrical transport of charge carriers in a given material. In this review, we have deliberated the physical concepts governing the materials to device performance as well as key challenges for enhancing the TE performance. Moreover, the role of crystal structure in the form of chemical bonding, crystal symmetry, order–disorder and phase transition on charge carrier transport in the material has been explored. Further, this review has also emphasized some insights on various approaches employed recently to improve the TE performance, such as, (i) carrier engineering via band engineering, low dimensional effects, and energy filtering effects and (ii) phonon engineering via doping/alloying, nano-structuring, embedding secondary phases in the matrix and microstructural engineering. We have also briefed the importance of magnetic elements on thermoelectric properties of the selected materials and spin Seebeck effect. Furthermore, the design and fabrication of TE modules and their major challenges are also discussed. As, thermoelectric figure of merit, zT does not have any theoretical limitation, an ideal high performance thermoelectric device should consist of low-cost, eco-friendly, efficient, n- or p-type materials that operate at wide-temperature range and similar coefficients of thermal expansion, suitable contact materials, less electrical/thermal losses and constant source of thermal energy. Overall, this review provides the recent physical concepts adopted and fabrication procedures of TE materials and device so as to improve the fundamental understanding and to develop a promising TE device.
References
More filters
TL;DR: In this paper, a detailed review of the role of the Berry phase effect in various solid state applications is presented. And a requantization method that converts a semiclassical theory to an effective quantum theory is demonstrated.
Abstract: Ever since its discovery, the Berry phase has permeated through all branches of physics. Over the last three decades, it was gradually realized that the Berry phase of the electronic wave function can have a profound effect on material properties and is responsible for a spectrum of phenomena, such as ferroelectricity, orbital magnetism, various (quantum/anomalous/spin) Hall effects, and quantum charge pumping. This progress is summarized in a pedagogical manner in this review. We start with a brief summary of necessary background, followed by a detailed discussion of the Berry phase effect in a variety of solid state applications. A common thread of the review is the semiclassical formulation of electron dynamics, which is a versatile tool in the study of electron dynamics in the presence of electromagnetic fields and more general perturbations. Finally, we demonstrate a re-quantization method that converts a semiclassical theory to an effective quantum theory. It is clear that the Berry phase should be added as a basic ingredient to our understanding of basic material properties.
3,344 citations
TL;DR: In this article, the anomalous Nernst effect was observed in chiral antiferromagnet Mn3Sn with a very small magnetization, and the transverse Seebeck coefficient at zero magnetic field reached ∼ 0.35?μV?K−1 at room temperature and ∼0.6?μ V?K −1 at 200?K, which is comparable to the maximum value known for a ferromagnetic metal.
Abstract: The anomalous Nernst effect is usually associated with ferromagnets — enabling a temperature gradient to generate a transverse electric field — but the Berry curvature associated with Weyl points can drive this phenomenon in chiral antiferromagnets. A temperature gradient in a ferromagnetic conductor can generate a transverse voltage drop perpendicular to both the magnetization and heat current. This anomalous Nernst effect has been considered to be proportional to the magnetization1,2,3,4,5,6,7, and thus observed only in ferromagnets. Theoretically, however, the anomalous Nernst effect provides a measure of the Berry curvature at the Fermi energy8,9, and so may be seen in magnets with no net magnetization. Here, we report the observation of a large anomalous Nernst effect in the chiral antiferromagnet Mn3Sn (ref. 10). Despite a very small magnetization ∼0.002?μB per Mn, the transverse Seebeck coefficient at zero magnetic field is ∼0.35?μV?K−1 at room temperature and reaches ∼0.6?μV?K−1 at 200?K, which is comparable to the maximum value known for a ferromagnetic metal. Our first-principles calculations reveal that this arises from a significantly enhanced Berry curvature associated with Weyl points near the Fermi energy11. As this effect is geometrically convenient for thermoelectric power generation—it enables a lateral configuration of modules to cover a heat source6—these observations suggest that a new class of thermoelectric materials could be developed that exploit topological magnets to fabricate efficient, densely integrated thermopiles.
456 citations
TL;DR: A finite-temperature formula for the orbital magnetization is derived, which enables to provide an explicit expression for the off-diagonal thermoelectric conductivity, to establish the Mott relation between the anomalous Nernst and Hall effects, and to reaffirm the Onsager relations between reciprocal thermoelectedric conductivities.
Abstract: We develop a theory of the Berry-phase effect in anomalous transport in ferromagnets driven by statistical forces such as the gradient of temperature or chemical potential. Here a charge Hall current arises from the Berry-phase correction to the orbital magnetization rather than from the anomalous velocity, which does not exist in the absence of a mechanical force. A finite-temperature formula for the orbital magnetization is derived, which enables us to provide an explicit expression for the off-diagonal thermoelectric conductivity, to establish the Mott relation between the anomalous Nernst and Hall effects, and to reaffirm the Onsager relations between reciprocal thermoelectric conductivities. A first-principles evaluation of our expression is carried out for the material ${\mathrm{CuCr}}_{2}{\mathrm{Se}}_{4\ensuremath{-}x}{\mathrm{Br}}_{x}$, obtaining quantitative agreement with a recent experiment.
399 citations
TL;DR: In this article, the existence of multiple Weyl points in the bulk and corresponding Fermi arcs on the surface was observed, predicting antiferromagnetic Weyl semimetals in Mn3Ge and Mn3Sn.
Abstract: Recent experiments revealed that Mn3Sn and Mn3Ge exhibit a strong anomalous Hall effect at room temperature, provoking us to explore their electronic structures for topological properties. By ab. initio band structure calculations, we have observed the existence of multiple Weyl points in the bulk and corresponding Fermi arcs on the surface, predicting antiferromagnetic Weyl semimetals in Mn3Ge and Mn3Sn. Here the chiral antiferromagnetism in the Kagome-type lattice structure is essential to determine the positions and numbers of Weyl points. Our work further reveals a new guiding principle to search for magnetic Weyl semimetals among materials that exhibit a strong anomalous Hall effect.
330 citations
TL;DR: In this article, the authors present a consistent method to separate thermoelectric and spin-orbit torque (SOT) measurements in ferromagnet/normal-metal bilayers, in which thermal gradient produced by Joule heating and SOT coexist and give rise to ac transverse signals with comparable symmetry and magnitude.
Abstract: We present harmonic transverse voltage measurements of current-induced thermoelectric and spin-orbit torque (SOT) effects in ferromagnet/normal-metal bilayers, in which thermal gradients produced by Joule heating and SOT coexist and give rise to ac transverse signals with comparable symmetry and magnitude. Based on the symmetry and field dependence of the transverse resistance, we develop a consistent method to separate thermoelectric and SOT measurements. By addressing first ferromagnet/light-metal bilayers with negligible spin-orbit coupling, we show that in-plane current injection induces a vertical thermal gradient whose sign and magnitude are determined by the resistivity difference and stacking order of the magnetic and nonmagnetic layers. We then study ferromagnet/heavy-metal bilayers with strong spin-orbit coupling, showing that second harmonic thermoelectric contributions to the transverse voltage may lead to a significant overestimation of the antidamping SOT. We find that thermoelectric effects are very strong in Ta(6 nm)/Co(2.5 nm) and negligible in Pt(6 nm)/Co(2.5 nm) bilayers. After including these effects in the analysis of the transverse voltage, we find that the antidamping SOTs in these bilayers, after normalization to the magnetization volume, are comparable to those found in thinner Co layers with perpendicular magnetization, whereas the fieldlike SOTs are about an order of magnitude smaller.
328 citations