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Sample records for seebeck effect

  1. Antiferromagnetic Spin Seebeck Effect.

    PubMed

    Wu, Stephen M; Zhang, Wei; Kc, Amit; Borisov, Pavel; Pearson, John E; Jiang, J Samuel; Lederman, David; Hoffmann, Axel; Bhattacharya, Anand

    2016-03-01

    We report on the observation of the spin Seebeck effect in antiferromagnetic MnF_{2}. A device scale on-chip heater is deposited on a bilayer of MnF_{2} (110) (30  nm)/Pt (4 nm) grown by molecular beam epitaxy on a MgF_{2} (110) substrate. Using Pt as a spin detector layer, it is possible to measure the thermally generated spin current from MnF_{2} through the inverse spin Hall effect. The low temperature (2-80 K) and high magnetic field (up to 140 kOe) regime is explored. A clear spin-flop transition corresponding to the sudden rotation of antiferromagnetic spins out of the easy axis is observed in the spin Seebeck signal when large magnetic fields (>9  T) are applied parallel to the easy axis of the MnF_{2} thin film. When the magnetic field is applied perpendicular to the easy axis, the spin-flop transition is absent, as expected. PMID:26991198

  2. Seebeck effect in molecular junctions.

    PubMed

    Zimbovskaya, Natalya A

    2016-05-11

    Advances in the fabrication and characterization of nanoscale systems presently allow for a better understanding of their thermoelectric properties. As is known, the building blocks of thermoelectricity are the Peltier and Seebeck effects. In the present work we review results of theoretical studies of the Seebeck effect in single-molecule junctions and similar systems. The behavior of thermovoltage and thermopower in these systems is controlled by several factors including the geometry of molecular bridges, the characteristics of contacts between the bridge and the electrodes, the strength of the Coulomb interactions between electrons on the bridge, and of electron-phonon interactions. We describe the impact of these factors on the thermopower. Also, we discuss a nonlinear Seebeck effect in molecular junctions. PMID:27073108

  3. Seebeck effect in molecular junctions

    NASA Astrophysics Data System (ADS)

    Zimbovskaya, Natalya A.

    2016-05-01

    Advances in the fabrication and characterization of nanoscale systems presently allow for a better understanding of their thermoelectric properties. As is known, the building blocks of thermoelectricity are the Peltier and Seebeck effects. In the present work we review results of theoretical studies of the Seebeck effect in single-molecule junctions and similar systems. The behavior of thermovoltage and thermopower in these systems is controlled by several factors including the geometry of molecular bridges, the characteristics of contacts between the bridge and the electrodes, the strength of the Coulomb interactions between electrons on the bridge, and of electron–phonon interactions. We describe the impact of these factors on the thermopower. Also, we discuss a nonlinear Seebeck effect in molecular junctions.

  4. Current heating induced spin Seebeck effect

    SciTech Connect

    Schreier, Michael Roschewsky, Niklas; Dobler, Erich; Meyer, Sibylle; Huebl, Hans; Goennenwein, Sebastian T. B.; Gross, Rudolf

    2013-12-09

    A measurement technique for the spin Seebeck effect is presented, wherein the normal metal layer used for its detection is exploited simultaneously as a resistive heater and thermometer. We show how the various contributions to the measured total signal can be disentangled, allowing to extract the voltage signal solely caused by the spin Seebeck effect. To this end, we performed measurements as a function of the external magnetic field strength and its orientation. We find that the effect scales linearly with the induced rise in temperature, as expected for the spin Seebeck effect.

  5. Paramagnetic and Antiferromagnetic Spin Seebeck Effect

    NASA Astrophysics Data System (ADS)

    Wu, Stephen

    We report on the observation of the longitudinal spin Seebeck effect in both antiferromagnetic and paramagnetic insulators. By using a microscale on-chip local heater, it is possible to generate a large thermal gradient confined to the chip surface without a large increase in the total sample temperature. This technique allows us to easily access low temperatures (200 mK) and high magnetic fields (14 T) through conventional dilution refrigeration and superconducting magnet setups. By exploring this regime, we detect the spin Seebeck effect through the spin-flop transition in antiferromagnetic MnF2 when a large magnetic field (>9 T) is applied along the easy axis direction. Using the same technique, we are also able to resolve a spin Seebeck effect from the paramagnetic phase of geometrically frustrated antiferromagnet Gd3Ga5O12 (gadolinium gallium garnet) and antiferromagnetic DyScO3 (DSO). Since these measurements occur above the ordering temperatures of these two materials, short-range magnetic order is implicated as the cause of the spin Seebeck effect in these systems. The discovery of the spin Seebeck effect in these two materials classes suggest that both antiferromagnetic spin waves and spin excitations from short range magnetic order may be used to generate spin current from insulators and that the spin wave spectra of individual materials are highly important to the specifics of the longitudinal spin Seebeck effect. Since insulating antiferromagnets and paramagnets are far more common than the typical insulating ferrimagnetic materials used in spin Seebeck experiments, this discovery opens up a large new class of materials for use in spin caloritronic devices. All authors acknowledge support of the U.S. Department of Energy (DOE), Office of Science, Basic Energy Sciences (BES), Materials Sciences and Engineering Division. The use of facilities at the Center for Nanoscale Materials, was supported by the U.S. DOE, BES under Contract No. DE-AC02-06CH11357.

  6. Spin pumping and spin Seebeck effect

    NASA Astrophysics Data System (ADS)

    Saitoh, Eiji

    2012-02-01

    Utilization of a spin current, a flow of electrons' spins in a solid, is the key technology in spintronics that will allow the achievement of efficient magnetic memories and computing devices. In this technology, generation and detection of spin currents are necessary. Here, we review inverse spin-Hall effect and spin-current-generation phenomena recently discovered both in metals and insulators: inverse spin-Hall effect, spin pumping, and spin Seebeck effect. (1)Spin pumping and spin torque in a Mott insulator system We found that spin pumping and spin torque effects appear also at an interface between Pt and an insulator YIG.. This means that we can connect a spin current carried by conduction electrons and a spin-wave spin current flowing in insulators. We demonstrate electric signal transmission by using these effects and interconversion of the spin currents [1]. (2) Spin Seebeck effect We have observed, by using the inverse spin-Hall effect [2], spin voltage generation from a heat current in a NiFe, named the spin-Seebeck effect [3]. Surprisingly, spin-Seebeck effect was found to appear even in insulators [4], a situation completely different from conventional charge Seebeck effect. The result implies an important role of elementary excitation in solids beside charge in the spin Seebeck effect. In the talk, we review the recent progress of the research on this effect. This research is collaboration with K. Ando, K. Uchida, Y. Kajiwara, S. Maekawa, G. E. W. Bauer, S. Takahashi, and J. Ieda. [4pt] [1] Y. Kajiwara and E. Saitoh et al. Nature 464 (2010) 262. [0pt] [2] E. Saitoh et al., Appl. Phys. Lett. 88 (2006) 182509. [0pt] [3] K. Uchida and E. Saitoh et al., Nature 455 (2008)778. [0pt] [4] K. Uchida and E. Saitoh et al.,Nature materials 9 (2010) 894 - 897.

  7. Exciton Seebeck effect in molecular systems

    SciTech Connect

    Yan, Yun-An; Cai, Shaohong

    2014-08-07

    We investigate the exciton dynamics under temperature difference with the hierarchical equations of motion. Through a nonperturbative simulation of the transient absorption of a heterogeneous trimer model, we show that the temperature difference causes exciton population redistribution and affects the exciton transfer time. It is found that one can reproduce not only the exciton population redistribution but also the change of the exciton transfer time induced by the temperature difference with a proper tuning of the site energies of the aggregate. In this sense, there exists a site energy shift equivalence for any temperature difference in a broad range. This phenomenon is similar to the Seebeck effect as well as spin Seebeck effect and can be named as exciton Seebeck effect.

  8. Time resolved spin Seebeck effect experiments

    SciTech Connect

    Roschewsky, Niklas Schreier, Michael; Schade, Felix; Ganzhorn, Kathrin; Meyer, Sibylle; Geprägs, Stephan; Kamra, Akashdeep; Huebl, Hans; Goennenwein, Sebastian T. B.; Gross, Rudolf

    2014-05-19

    In this Letter, we present the results of transient thermopower experiments, performed at room temperature on yttrium iron garnet/platinum bilayers. Upon application of a time-varying thermal gradient, we observe a characteristic low-pass frequency response of the ensuing thermopower voltage with cutoff frequencies of up to 37 MHz. We interpret our results in terms of the spin Seebeck effect, and argue that small wavevector magnons are of minor importance for the spin Seebeck effect in our thin film hybrid structures.

  9. Spin Seebeck effect in a weak ferromagnet

    NASA Astrophysics Data System (ADS)

    Arboleda, Juan David; Arnache Olmos, Oscar; Aguirre, Myriam Haydee; Ramos, Rafael; Anadon, Alberto; Ibarra, Manuel Ricardo

    2016-06-01

    We report the observation of room temperature spin Seebeck effect (SSE) in a weak ferromagnetic normal spinel Zinc Ferrite (ZFO). Despite the weak ferromagnetic behavior, the measurements of the SSE in ZFO show a thermoelectric voltage response comparable with the reported values for other ferromagnetic materials. Our results suggest that SSE might possibly originate from the surface magnetization of the ZFO.

  10. Simple Demonstration of the Seebeck Effect

    ERIC Educational Resources Information Center

    Molki, Arman

    2010-01-01

    In this article we propose a simple and low-cost experimental set-up through which science educators can demonstrate the Seebeck effect using a thermocouple and an instrumentation amplifier. The experiment can be set up and conducted during a 1-hour laboratory session. (Contains 3 tables and 3 figures.)

  11. Seebeck effect at the atomic scale.

    PubMed

    Lee, Eui-Sup; Cho, Sanghee; Lyeo, Ho-Ki; Kim, Yong-Hyun

    2014-04-01

    The atomic variations of electronic wave functions at the surface and electron scattering near a defect have been detected unprecedentedly by tracing thermoelectric voltages given a temperature bias [Cho et al., Nat. Mater. 12, 913 (2013)]. Because thermoelectricity, or the Seebeck effect, is associated with heat-induced electron diffusion, how the thermoelectric signal is related to the atomic-scale wave functions and what the role of the temperature is at such a length scale remain very unclear. Here we show that coherent electron and heat transport through a pointlike contact produces an atomic Seebeck effect, which is described by the mesoscopic Seebeck coefficient multiplied by an effective temperature drop at the interface. The mesoscopic Seebeck coefficient is approximately proportional to the logarithmic energy derivative of local density of states at the Fermi energy. We deduced that the effective temperature drop at the tip-sample junction could vary at a subangstrom scale depending on atom-to-atom interaction at the interface. A computer-based simulation method of thermoelectric images is proposed, and a point defect in graphene was identified by comparing experiment and the simulation of thermoelectric imaging. PMID:24745445

  12. Magnons, Spin Current and Spin Seebeck Effect

    NASA Astrophysics Data System (ADS)

    Maekawa, Sadamichi

    2012-02-01

    When metals and semiconductors are placed in a temperature gradient, the electric voltage is generated. This mechanism to convert heat into electricity, the so-called Seebeck effect, has attracted much attention recently as the mechanism for utilizing wasted heat energy. [1]. Ferromagnetic insulators are good conductors of spin current, i.e., the flow of electron spins [2]. When they are placed in a temperature gradient, generated are magnons, spin current and the spin voltage [3], i.e., spin accumulation. Once the spin voltage is converted into the electric voltage by inverse spin Hall effect in attached metal films such as Pt, the electric voltage is obtained from heat energy [4-5]. This is called the spin Seebeck effect. Here, we present the linear-response theory of spin Seebeck effect based on the fluctuation-dissipation theorem [6-8] and discuss a variety of the devices. [4pt] [1] S. Maekawa et al, Physics of Transition Metal Oxides (Springer, 2004). [0pt] [2] S. Maekawa: Nature Materials 8, 777 (2009). [0pt] [3] Concept in Spin Electronics, eds. S. Maekawa (Oxford University Press, 2006). [0pt] [4] K. Uchida et al., Nature 455, 778 (2008). [0pt] [5] K. Uchida et al., Nature Materials 9, 894 (2010) [0pt] [6] H. Adachi et al., APL 97, 252506 (2010) and Phys. Rev. B 83, 094410 (2011). [0pt] [7] J. Ohe et al., Phys. Rev. B (2011) [0pt] [8] K. Uchida et al., Appl. Phys. Lett. 97, 104419 (2010).

  13. Spin Seebeck effect at microwave frequencies

    NASA Astrophysics Data System (ADS)

    Schreier, Michael; Kramer, Franz; Huebl, Hans; Geprägs, Stephan; Gross, Rudolf; Goennenwein, Sebastian T. B.; Noack, Timo; Langner, Thomas; Serga, Alexander A.; Hillebrands, Burkard; Vasyuchka, Vitaliy I.

    2016-06-01

    We experimentally study the transient voltage response of yttrium iron garnet/platinum bilayer samples subject to periodic heating up to gigahertz frequencies. We observe an intrinsic cutoff frequency of the induced thermopower voltage, which characteristically depends on the thickness of the yttrium iron garnet film. The cutoff frequency reaches values of up to 350 MHz in a 50-nm-thick yttrium iron garnet film, but drops to below 1 MHz for several-micrometer-thick films. These data corroborate the notion that the magnon spectrum responsible for the spin current emission in the spin Seebeck effect can be shaped by tuning the thickness of the ferromagnetic layer.

  14. Surface sensitivity of the spin Seebeck effect

    SciTech Connect

    Aqeel, A.; Vera-Marun, I. J.; Wees, B. J. van; Palstra, T. T. M.

    2014-10-21

    We have investigated the influence of the interface quality on the spin Seebeck effect (SSE) of the bilayer system yttrium iron garnet (YIG)–platinum (Pt). The magnitude and shape of the SSE is strongly influenced by mechanical treatment of the YIG single crystal surface. We observe that the saturation magnetic field (H{sub sat}{sup SSE}) for the SSE signal increases from 55.3 mT to 72.8 mT with mechanical treatment. The change in the magnitude of H{sub sat}{sup SSE} can be attributed to the presence of a perpendicular magnetic anisotropy due to the treatment induced surface strain or shape anisotropy in the Pt/YIG system. Our results show that the SSE is a powerful tool to investigate magnetic anisotropy at the interface.

  15. Large Seebeck effect by charge-mobility engineering

    PubMed Central

    Sun, Peijie; Wei, Beipei; Zhang, Jiahao; Tomczak, Jan M.; Strydom, A.M.; Søndergaard, M.; Iversen, Bo B.; Steglich, Frank

    2015-01-01

    The Seebeck effect describes the generation of an electric potential in a conducting solid exposed to a temperature gradient. In most cases, it is dominated by an energy-dependent electronic density of states at the Fermi level, in line with the prevalent efforts towards superior thermoelectrics through the engineering of electronic structure. Here we demonstrate an alternative source for the Seebeck effect based on charge-carrier relaxation: a charge mobility that changes rapidly with temperature can result in a sizeable addition to the Seebeck coefficient. This new Seebeck source is demonstrated explicitly for Ni-doped CoSb3, where a marked mobility change occurs due to the crossover between two different charge-relaxation regimes. Our findings unveil the origin of pronounced features in the Seebeck coefficient of many other elusive materials characterized by a significant mobility mismatch. When utilized appropriately, this effect can also provide a novel route to the design of improved thermoelectric materials. PMID:26108283

  16. Nernst and Seebeck effects in a graphene nanoribbon

    NASA Astrophysics Data System (ADS)

    Xing, Yanxia; Sun, Qing-Feng; Wang, Jian

    2009-12-01

    The thermoelectric power, including the Nernst and Seebeck effects, in graphene nanoribbon is studied. By using the nonequilibrium Green’s function combining with the tight-binding Hamiltonian, the Nernst and Seebeck coefficients are obtained. Due to the electron-hole symmetry, the Nernst coefficient is an even function of the Fermi energy while the Seebeck coefficient is an odd function regardless of the magnetic field. In the presence of a strong magnetic field, the Nernst and Seebeck coefficients are almost independent of the chirality and width of the nanoribbon, and they show peaks when the Fermi energy crosses the Landau levels. The height of nth (excluding n=0 ) peak is [ln2/|n|] for the Nernst effect and is [ln2/n] for the Seebeck effect. For the zeroth peak, it is abnormal with height [2ln2] for the Nernst effect and the peak disappears for the Seebeck effect. When the magnetic field is turned off, however, the Nernst effect is absent and only Seebeck effect exists. In this case, the Seebeck coefficient strongly depends on the chirality of the nanoribbon. The peaks are equidistant for the nanoribbons with zigzag edge but are irregularly distributed for the armchair edge. In particular, for the insulating armchair ribbon, the Seebeck coefficient can be very large near the Dirac point. When the magnetic field varies from zero to large values, the differences among the Seebeck coefficients for different chiral ribbons gradually vanish and the nonzero value of Nernst coefficient appears first near the Dirac point then gradually extends to the whole energy region.

  17. An analytical solution for quantum size effects on Seebeck coefficient

    NASA Astrophysics Data System (ADS)

    Karabetoglu, S.; Sisman, A.; Ozturk, Z. F.

    2016-03-01

    There are numerous experimental and numerical studies about quantum size effects on Seebeck coefficient. In contrast, in this study, we obtain analytical expressions for Seebeck coefficient under quantum size effects. Seebeck coefficient of a Fermi gas confined in a rectangular domain is considered. Analytical expressions, which represent the size dependency of Seebeck coefficient explicitly, are derived in terms of confinement parameters. A fundamental form of Seebeck coefficient based on infinite summations is used under relaxation time approximation. To obtain analytical results, summations are calculated using the first two terms of Poisson summation formula. It is shown that they are in good agreement with the exact results based on direct calculation of summations as long as confinement parameters are less than unity. The analytical results are also in good agreement with experimental and numerical ones in literature. Maximum relative errors of analytical expressions are less than 3% and 4% for 2D and 1D cases, respectively. Dimensional transitions of Seebeck coefficient are also examined. Furthermore, a detailed physical explanation for the oscillations in Seebeck coefficient is proposed by considering the relative standard deviation of total variance of particle number in Fermi shell.

  18. Longitudinal spin Seebeck effect contribution in transverse spin Seebeck effect experiments in Pt/YIG and Pt/NFO.

    PubMed

    Meier, Daniel; Reinhardt, Daniel; van Straaten, Michael; Klewe, Christoph; Althammer, Matthias; Schreier, Michael; Goennenwein, Sebastian T B; Gupta, Arunava; Schmid, Maximilian; Back, Christian H; Schmalhorst, Jan-Michael; Kuschel, Timo; Reiss, Günter

    2015-01-01

    The spin Seebeck effect, the generation of a spin current by a temperature gradient, has attracted great attention, but the interplay over a millimetre range along a thin ferromagnetic film as well as unintended side effects which hinder an unambiguous detection have evoked controversial discussions. Here, we investigate the inverse spin Hall voltage of a 10 nm thin Pt strip deposited on the magnetic insulators Y3Fe5O12 and NiFe2O4 with a temperature gradient in the film plane. We show characteristics typical of the spin Seebeck effect, although we do not observe the most striking features of the transverse spin Seebeck effect. Instead, we attribute the observed voltages to the longitudinal spin Seebeck effect generated by a contact tip induced parasitic out-of-plane temperature gradient, which depends on material, diameter and temperature of the tip. PMID:26394541

  19. Longitudinal spin Seebeck effect contribution in transverse spin Seebeck effect experiments in Pt/YIG and Pt/NFO

    PubMed Central

    Meier, Daniel; Reinhardt, Daniel; van Straaten, Michael; Klewe, Christoph; Althammer, Matthias; Schreier, Michael; Goennenwein, Sebastian T. B.; Gupta, Arunava; Schmid, Maximilian; Back, Christian H.; Schmalhorst, Jan-Michael; Kuschel, Timo; Reiss, Günter

    2015-01-01

    The spin Seebeck effect, the generation of a spin current by a temperature gradient, has attracted great attention, but the interplay over a millimetre range along a thin ferromagnetic film as well as unintended side effects which hinder an unambiguous detection have evoked controversial discussions. Here, we investigate the inverse spin Hall voltage of a 10 nm thin Pt strip deposited on the magnetic insulators Y3Fe5O12 and NiFe2O4 with a temperature gradient in the film plane. We show characteristics typical of the spin Seebeck effect, although we do not observe the most striking features of the transverse spin Seebeck effect. Instead, we attribute the observed voltages to the longitudinal spin Seebeck effect generated by a contact tip induced parasitic out-of-plane temperature gradient, which depends on material, diameter and temperature of the tip. PMID:26394541

  20. Gigantic enhancement of spin Seebeck effect by phonon drag

    NASA Astrophysics Data System (ADS)

    Adachi, Hiroto; Uchida, Ken-Ichi; Saitoh, Eiji; Ohe, Jun-Ichiro; Takahashi, Saburo; Maekawa, Sadamichi

    2011-03-01

    We investigate both theoretically and experimentally a gigantic enhancement of the spin Seebeck effect [K. Uchida et al., Nature 455, 778 (2008); C. M. Jaworski et al., Nature Mater. 9, 898 (2010); K. Uchida et al., Nature Mater. 9, 894 (2010)] in a prototypical magnet La Y2 Fe 5 O12 at low temperatures. Our theoretical analysis sheds light on the important role of phonons; the spin Seebeck effect is enormously enhanced by nonequilibrium phonons that drag the low-lying spin excitations. We further argue that this scenario gives a clue to understand the observation of the spin Seebeck effect that is unaccompanied by a global spin current, and predict that the substrate condition affects the observed signal.

  1. Longitudinal spin Seebeck effect: from fundamentals to applications.

    PubMed

    Uchida, K; Ishida, M; Kikkawa, T; Kirihara, A; Murakami, T; Saitoh, E

    2014-08-27

    The spin Seebeck effect refers to the generation of spin voltage as a result of a temperature gradient in ferromagnetic or ferrimagnetic materials. When a conductor is attached to a magnet under a temperature gradient, the thermally generated spin voltage in the magnet injects a spin current into the conductor, which in turn produces electric voltage owing to the spin-orbit interaction. The spin Seebeck effect is of increasing importance in spintronics, since it enables direct generation of a spin current from heat and appears in a variety of magnets ranging from metals and semiconductors to insulators. Recent studies on the spin Seebeck effect have been conducted mainly in paramagnetic metal/ferrimagnetic insulator junction systems in the longitudinal configuration in which a spin current flowing parallel to the temperature gradient is measured. This 'longitudinal spin Seebeck effect' (LSSE) has been observed in various sample systems and exclusively established by separating the spin-current contribution from extrinsic artefacts, such as conventional thermoelectric and magnetic proximity effects. The LSSE in insulators also provides a novel and versatile pathway to thermoelectric generation in combination of the inverse spin-Hall effects. In this paper, we review basic experiments on the LSSE and discuss its potential thermoelectric applications with several demonstrations. PMID:25105889

  2. Magnetic field control of the spin Seebeck effect

    NASA Astrophysics Data System (ADS)

    Ritzmann, Ulrike; Hinzke, Denise; Kehlberger, Andreas; Guo, Er-Jia; Kläui, Mathias; Nowak, Ulrich

    2015-11-01

    The origin of the suppression of the longitudinal spin Seebeck effect by applied magnetic fields is studied. We perform numerical simulations of the stochastic Landau-Lifshitz-Gilbert equation of motion for an atomistic spin model and calculate the magnon accumulation in linear temperature gradients for different strengths of applied magnetic fields and different length scales of the temperature gradient. We observe a decrease of the magnon accumulation with increasing magnetic field and we reveal that the origin of this effect is a field dependent change of the frequency distribution of the propagating magnons. With increasing field the magnonic spin currents are reduced due to a suppression of parts of the frequency spectrum. By comparison with measurements of the magnetic field dependent longitudinal spin Seebeck effect in YIG thin films with various thicknesses, we find qualitative agreement between our model and the experimental data, demonstrating the importance of this effect for experimental systems.

  3. Evaluation of thermal gradients in longitudinal spin Seebeck effect measurements

    NASA Astrophysics Data System (ADS)

    Sola, A.; Kuepferling, M.; Basso, V.; Pasquale, M.; Kikkawa, T.; Uchida, K.; Saitoh, E.

    2015-05-01

    In the framework of the longitudinal spin Seebeck effect (LSSE), we developed an experimental setup for the characterization of LSSE devices. This class of device consists in a layered structure formed by a substrate, a ferrimagnetic insulator (YIG) where the spin current is thermally generated, and a paramagnetic metal (Pt) for the detection of the spin current via the inverse spin-Hall effect. In this kind of experiments, the evaluation of a thermal gradient through the thin YIG layer is a crucial point. In this work, we perform an indirect determination of the thermal gradient through the measurement of the heat flux. We developed an experimental setup using Peltier cells that allow us to measure the heat flux through a given sample. In order to test the technique, a standard LSSE device produced at Tohoku University was measured. We find a spin Seebeck SSSE coefficient of 2.8 × 10 - 7 V K-1.

  4. Seebeck effect in a battery-type thermocell

    NASA Astrophysics Data System (ADS)

    Kobayashi, Wataru; Kinoshita, Akemi; Moritomo, Yutaka

    2015-08-01

    We demonstrated that battery-type thermocells, which consist of two paste-type electrodes with the same active material and electrolyte, show the Seebeck effect. The magnitudes of electrochemical Seebeck coefficient (S) of the thermocells with several layered oxides were evaluated: -12.7 μV/K for Na0.99CoO2, -29.7 μV/K for Na0.52MnO2, -22.4 μV/K for Na0.51Mn0.5Fe0.5O2, and -6.8 μV/K for LiCoO2. In the thermocell with Na0.99CoO2, time-dependence of the electromotive force (ΔV) at a constant temperature difference (ΔT) was well reproduced by a mean-field approach of the chemical potential ( ϕ)—Na+ concentration (x) relationship, indicating that the Na+ intercalation/deintercalation plays an intrinsic role in the electrochemical Seebeck effect.

  5. Enhanced Thermoelectric Performance and Anomalous Seebeck Effects in Topological Insulators

    NASA Astrophysics Data System (ADS)

    Xu, Yong; Gan, Zhongxue; Zhang, Shou-Cheng

    2014-06-01

    Improving the thermoelectric figure of merit zT is one of the greatest challenges in material science. The recent discovery of topological insulators (TIs) offers new promise in this prospect. In this work, we demonstrate theoretically that zT is strongly size dependent in TIs, and the size parameter can be tuned to enhance zT to be significantly greater than 1. Furthermore, we show that the lifetime of the edge states in TIs is strongly energy dependent, leading to large and anomalous Seebeck effects with an opposite sign to the Hall effect. These striking properties make TIs a promising material for thermoelectric science and technology.

  6. Skyrmionic spin Seebeck effect via dissipative thermomagnonic torques

    NASA Astrophysics Data System (ADS)

    Kovalev, Alexey A.

    2014-06-01

    We derive thermomagnonic torque and its "β-type" dissipative correction from the stochastic Landau-Lifshitz-Gilbert equation. The β-type dissipative correction describes viscous coupling between magnetic dynamics and magnonic current and it stems from spin mistracking of the magnetic order. We show that thermomagnonic torque is important for describing temperature gradient induced motion of skyrmions in helical magnets while dissipative correction plays an essential role in generating transverse Magnus force. We propose to detect such skyrmionic motion by employing the transverse spin Seebeck effect geometry.

  7. Spin Seebeck effect in YIG-based systems

    NASA Astrophysics Data System (ADS)

    Siegel, Gene; Prestgard, Megan; Teng, Shiang; Tiwari, Ashutosh

    2015-03-01

    Recently, the use of magnetic insulators (yttrium iron garnet, YIG) in conjunction with platinum has sparked interest in spintronics research. This is due to the existence of the spin Seebeck effect which could potentially be a source of pure spin current for spintronic devices. Furthermore, these coatings could potentially show the versatility of spintronics by acting as a spin-based thermoelectric generator, thereby providing a new method of transforming heat into power. However, there remain questions regarding the origins and legitimacy of the spin Seebeck effect. Moreover, recent publications claim that the observed effects are a manifestation of magnetic proximity effects in platinum and not a true SSE signal. Because of these concerns, we are providing supporting evidence that the voltages observed in the YIG/Pt films are truly SSE voltages. We are reaffirming claims that magnon transport theory provides an accurate basis for explaining SSE behavior. Finally, we illustrate the advantages of pulsed laser deposition, as these YIG films possess a large SSE voltage compared to those films grown using liquid phase deposition techniques.

  8. Evaluation of thermal gradients in longitudinal spin Seebeck effect measurements

    SciTech Connect

    Sola, A. Kuepferling, M.; Basso, V.; Pasquale, M.; Kikkawa, T.; Uchida, K.; Saitoh, E.

    2015-05-07

    In the framework of the longitudinal spin Seebeck effect (LSSE), we developed an experimental setup for the characterization of LSSE devices. This class of device consists in a layered structure formed by a substrate, a ferrimagnetic insulator (YIG) where the spin current is thermally generated, and a paramagnetic metal (Pt) for the detection of the spin current via the inverse spin-Hall effect. In this kind of experiments, the evaluation of a thermal gradient through the thin YIG layer is a crucial point. In this work, we perform an indirect determination of the thermal gradient through the measurement of the heat flux. We developed an experimental setup using Peltier cells that allow us to measure the heat flux through a given sample. In order to test the technique, a standard LSSE device produced at Tohoku University was measured. We find a spin Seebeck S{sub SSE} coefficient of 2.8×10{sup −7} V K{sup −1}.

  9. Thermal Conductance and Seebeck Effect in Mesoscopic Systems

    NASA Astrophysics Data System (ADS)

    Aly, Arafa H.; El-Gawaad, N. S. Abd

    2015-11-01

    In this work, thermoelectric transport through a saddle-point potential is discussed with an emphasis on the effects of the chemical potential and temperature. In particular, the thermal conductance and the Seebeck coefficient are calculated for two-dimensional systems of a constriction defined by a saddle-point potential. The solution as a function of temperature and chemical potential has been investigated. The Peltier coefficient and thermal transport in a quantum point contact (QPC), under the influence of external fields and different temperatures, are presented. Also, the oscillations of the Peltier coefficient in external fields are obtained. Numerical calculations of the Peltier coefficient are performed at different applied voltages, amplitudes, and temperatures. Moreover, a method is proposed for measuring the sub-band energies and spin-splitting energies in a bottle-neck of the constriction. For weak non-linearities, the charge and entropy currents across a QPC are expanded as a series in powers of the applied bias voltage and the temperature difference. Expansions of the Seebeck voltage in terms of the temperature difference and the Peltier heat in terms of the current are obtained.

  10. Microscopic origin of subthermal magnons and the spin Seebeck effect

    NASA Astrophysics Data System (ADS)

    Diniz, I.; Costa, A. T.

    2016-05-01

    Recent experimental evidence points to low-energy magnons as the primary contributors to the spin Seebeck effect. This spectral dependence is puzzling since it is not observed on other thermocurrents in the same material. Here, we argue that the physical origin of this behavior is the magnon–magnon scattering mediated by phonons, in a process which conserves the number of magnons. To assess the importance and features of this kind of scattering, we derive the effective magnon–phonon interaction from a microscopic model, including band energy, a screened electron–electron interaction and the electron–phonon interaction. Unlike higher order magnon-only scattering, we find that the coupling with phonons induce a scattering which is very small for low-energy (or subthermal) magnons but increases sharply above a certain energy—rendering magnons above this energy poor spin-current transporters.

  11. Origin of the spin Seebeck effect in compensated ferrimagnets

    PubMed Central

    Geprägs, Stephan; Kehlberger, Andreas; Coletta, Francesco Della; Qiu, Zhiyong; Guo, Er-Jia; Schulz, Tomek; Mix, Christian; Meyer, Sibylle; Kamra, Akashdeep; Althammer, Matthias; Huebl, Hans; Jakob, Gerhard; Ohnuma, Yuichi; Adachi, Hiroto; Barker, Joseph; Maekawa, Sadamichi; Bauer, Gerrit E. W.; Saitoh, Eiji; Gross, Rudolf; Goennenwein, Sebastian T. B.; Kläui, Mathias

    2016-01-01

    Magnons are the elementary excitations of a magnetically ordered system. In ferromagnets, only a single band of low-energy magnons needs to be considered, but in ferrimagnets the situation is more complex owing to different magnetic sublattices involved. In this case, low lying optical modes exist that can affect the dynamical response. Here we show that the spin Seebeck effect (SSE) is sensitive to the complexities of the magnon spectrum. The SSE is caused by thermally excited spin dynamics that are converted to a voltage by the inverse spin Hall effect at the interface to a heavy metal contact. By investigating the temperature dependence of the SSE in the ferrimagnet gadolinium iron garnet, with a magnetic compensation point near room temperature, we demonstrate that higher-energy exchange magnons play a key role in the SSE. PMID:26842873

  12. Nonequilibrium thermodynamics of the spin Seebeck and spin Peltier effects

    NASA Astrophysics Data System (ADS)

    Basso, Vittorio; Ferraro, Elena; Magni, Alessandro; Sola, Alessandro; Kuepferling, Michaela; Pasquale, Massimo

    2016-05-01

    We study the problem of magnetization and heat currents and their associated thermodynamic forces in a magnetic system by focusing on the magnetization transport in ferromagnetic insulators like YIG. The resulting theory is applied to the longitudinal spin Seebeck and spin Peltier effects. By focusing on the specific geometry with one Y3Fe5O12 (YIG) layer and one Pt layer, we obtain the optimal conditions for generating large magnetization currents into Pt or large temperature effects in YIG. The theoretical predictions are compared with experiments from the literature permitting to derive the values of the thermomagnetic coefficients of YIG: the magnetization diffusion length lM˜0.4 μ m and the absolute thermomagnetic power coefficient ɛM˜10-2TK-1 .

  13. Origin of the spin Seebeck effect in compensated ferrimagnets.

    PubMed

    Geprägs, Stephan; Kehlberger, Andreas; Della Coletta, Francesco; Qiu, Zhiyong; Guo, Er-Jia; Schulz, Tomek; Mix, Christian; Meyer, Sibylle; Kamra, Akashdeep; Althammer, Matthias; Huebl, Hans; Jakob, Gerhard; Ohnuma, Yuichi; Adachi, Hiroto; Barker, Joseph; Maekawa, Sadamichi; Bauer, Gerrit E W; Saitoh, Eiji; Gross, Rudolf; Goennenwein, Sebastian T B; Kläui, Mathias

    2016-01-01

    Magnons are the elementary excitations of a magnetically ordered system. In ferromagnets, only a single band of low-energy magnons needs to be considered, but in ferrimagnets the situation is more complex owing to different magnetic sublattices involved. In this case, low lying optical modes exist that can affect the dynamical response. Here we show that the spin Seebeck effect (SSE) is sensitive to the complexities of the magnon spectrum. The SSE is caused by thermally excited spin dynamics that are converted to a voltage by the inverse spin Hall effect at the interface to a heavy metal contact. By investigating the temperature dependence of the SSE in the ferrimagnet gadolinium iron garnet, with a magnetic compensation point near room temperature, we demonstrate that higher-energy exchange magnons play a key role in the SSE. PMID:26842873

  14. Origin of the spin Seebeck effect in compensated ferrimagnets

    NASA Astrophysics Data System (ADS)

    Geprägs, Stephan; Kehlberger, Andreas; Coletta, Francesco Della; Qiu, Zhiyong; Guo, Er-Jia; Schulz, Tomek; Mix, Christian; Meyer, Sibylle; Kamra, Akashdeep; Althammer, Matthias; Huebl, Hans; Jakob, Gerhard; Ohnuma, Yuichi; Adachi, Hiroto; Barker, Joseph; Maekawa, Sadamichi; Bauer, Gerrit E. W.; Saitoh, Eiji; Gross, Rudolf; Goennenwein, Sebastian T. B.; Kläui, Mathias

    2016-02-01

    Magnons are the elementary excitations of a magnetically ordered system. In ferromagnets, only a single band of low-energy magnons needs to be considered, but in ferrimagnets the situation is more complex owing to different magnetic sublattices involved. In this case, low lying optical modes exist that can affect the dynamical response. Here we show that the spin Seebeck effect (SSE) is sensitive to the complexities of the magnon spectrum. The SSE is caused by thermally excited spin dynamics that are converted to a voltage by the inverse spin Hall effect at the interface to a heavy metal contact. By investigating the temperature dependence of the SSE in the ferrimagnet gadolinium iron garnet, with a magnetic compensation point near room temperature, we demonstrate that higher-energy exchange magnons play a key role in the SSE.

  15. Spectral characteristics of time resolved magnonic spin Seebeck effect

    NASA Astrophysics Data System (ADS)

    Etesami, S. R.; Chotorlishvili, L.; Berakdar, J.

    2015-09-01

    Spin Seebeck effect (SSE) holds promise for new spintronic devices with low-energy consumption. The underlying physics, essential for a further progress, is yet to be fully clarified. This study of the time resolved longitudinal SSE in the magnetic insulator yttrium iron garnet concludes that a substantial contribution to the spin current stems from small wave-vector subthermal exchange magnons. Our finding is in line with the recent experiment by S. R. Boona and J. P. Heremans [Phys. Rev. B 90, 064421 (2014)]. Technically, the spin-current dynamics is treated based on the Landau-Lifshitz-Gilbert equation also including magnons back-action on thermal bath, while the formation of the time dependent thermal gradient is described self-consistently via the heat equation coupled to the magnetization dynamics.

  16. Spectral characteristics of time resolved magnonic spin Seebeck effect

    SciTech Connect

    Etesami, S. R.; Chotorlishvili, L.; Berakdar, J.

    2015-09-28

    Spin Seebeck effect (SSE) holds promise for new spintronic devices with low-energy consumption. The underlying physics, essential for a further progress, is yet to be fully clarified. This study of the time resolved longitudinal SSE in the magnetic insulator yttrium iron garnet concludes that a substantial contribution to the spin current stems from small wave-vector subthermal exchange magnons. Our finding is in line with the recent experiment by S. R. Boona and J. P. Heremans [Phys. Rev. B 90, 064421 (2014)]. Technically, the spin-current dynamics is treated based on the Landau-Lifshitz-Gilbert equation also including magnons back-action on thermal bath, while the formation of the time dependent thermal gradient is described self-consistently via the heat equation coupled to the magnetization dynamics.

  17. Amplification of spin waves by the spin Seebeck effect

    NASA Astrophysics Data System (ADS)

    Padrón-Hernández, E.; Azevedo, A.; Rezende, S. M.

    2012-04-01

    We observe amplification of spin-wave packets propagating along a film of single-crystal yttrium iron garnet (YIG) subject to a transverse temperature gradient. The spin waves are excited and detected with standard techniques used to study volume or surface magnetostatic waves in the 1-2 GHz frequency range. Amplification gains larger than 20 are observed in a YIG film heated by a current of 20 mA in a Pt layer in a simple YIG/Pt bilayer. The amplification is attributed to the action of a spin-transfer thermal torque acting on the magnetization that opposes the relaxation and which is created by spin currents generated through the spin Seebeck effect. The experimental data are interpreted with a spin-wave model.

  18. Theory of the spin Seebeck effect in antiferromagnets

    NASA Astrophysics Data System (ADS)

    Rezende, S. M.; Rodríguez-Suárez, R. L.; Azevedo, A.

    2016-01-01

    The spin Seebeck effect (SSE) consists in the generation of a spin current by a temperature gradient applied in a magnetic film. The SSE is usually detected by an electric voltage generated in a metallic layer in contact with the magnetic film resulting from the conversion of the spin current into charge current by means of the inverse spin Hall effect. The SSE has been widely studied in bilayers made of the insulating ferrimagnet yttrium iron garnet (YIG) and metals with large spin-orbit coupling such as platinum. Recently the SSE has been observed in bilayers made of the antiferromagnet Mn F2 and Pt, revealing dependences of the SSE voltage on temperature and field very different from the ones observed in YIG/Pt. Here we present a theory for the SSE in structures with an antiferromagnetic insulator (AFI) in contact with a normal metal (NM) that relies on the bulk magnon spin current created by the temperature gradient across the thickness of the AFI/NM bilayer. The theory explains quite well the measured dependences of the SSE voltage on the sample temperature and on the applied magnetic field in Mn F2/Pt .

  19. Magneto-Seebeck effect in spin-valve with in-plane thermal gradient

    SciTech Connect

    Jain, S. Bose, A. Palkar, V. R. Tulapurkar, A. A.; Lam, D. D. Suzuki, Y.; Sharma, H. Tomy, C. V.

    2014-12-15

    We present measurements of magneto-Seebeck effect on a spin valve with in-plane thermal gradient. We measured open circuit voltage and short circuit current by applying a temperature gradient across a spin valve stack, where one of the ferromagnetic layers is pinned. We found a clear hysteresis in these two quantities as a function of magnetic field. From these measurements, the magneto-Seebeck effect was found to be same as magneto-resistance effect.

  20. Spin-dependent Seebeck effects in a graphene nanoribbon coupled to two square lattice ferromagnetic leads

    SciTech Connect

    Zhou, Benhu Zeng, Yangsu; Zhou, Benliang; Zhou, Guanghui; Ouyang, Tao

    2015-03-14

    We theoretically investigate spin-dependent Seebeck effects for a system consisting of a narrow graphene nanoribbon (GNR) contacted to square lattice ferromagnetic (FM) electrodes with noncollinear magnetic moments. Both zigzag-edge graphene nanoribbons (ZGNRs) and armchair-edge graphene nanoribbons (AGNRs) were considered. Compared with our previous work with two-dimensional honeycomb-lattice FM leads, a more realistic model of two-dimensional square-lattice FM electrodes is adopted here. Using the nonequilibrium Green's function method combining with the tight-binding Hamiltonian, it is demonstrated that both the charge Seebeck coefficient S{sub C} and the spin-dependent Seebeck coefficient S{sub S} strongly depend on the geometrical contact between the GNR and the leads. In our previous work, S{sub C} for a semiconducting 15-AGNR system near the Dirac point is two orders of magnitude larger than that of a metallic 17-AGNR system. However, S{sub C} is the same order of magnitude for both metallic 17-AGNR and semiconducting 15-AGNR systems in the present paper because of the lack of a transmission energy gap for the 15-AGNR system. Furthermore, the spin-dependent Seebeck coefficient S{sub S} for the systems with 20-ZGNR, 17-AGNR, and 15-AGNR is of the same order of magnitude and its maximum absolute value can reach 8 μV/K. The spin-dependent Seebeck effects are not very pronounced because the transmission coefficient weakly depends on spin orientation. Moreover, the spin-dependent Seebeck coefficient is further suppressed with increasing angle between the relative alignments of magnetization directions of the two leads. Additionally, the spin-dependent Seebeck coefficient can be strongly suppressed for larger disorder strength. The results obtained here may provide valuable theoretical guidance in the experimental design of heat spintronic devices.

  1. Spin-dependent Seebeck effect in Aharonov-Bohm rings with Rashba and Dresselhaus spin-orbit interactions

    NASA Astrophysics Data System (ADS)

    Liu, Bin; Li, Yunyun; Zhou, Jun; Nakayama, Tsuneyoshi; Li, Baowen

    2016-06-01

    We theoretically investigate the spin-dependent Seebeck effect in an Aharonov-Bohm mesoscopic ring in the presence of both Rashba and Dresselhaus spin-orbit interactions under magnetic flux perpendicular to the ring. We apply the Green's function method to calculate the spin Seebeck coefficient employing the tight-binding Hamiltonian. It is found that the spin Seebeck coefficient is proportional to the slope of the energy-dependent transmission coefficients. We study the strong dependence of spin Seebeck coefficient on the Fermi energy, magnetic flux, strength of spin-orbit coupling, and temperature. Maximum spin Seebeck coefficients can be obtained when the strengths of Rashba and Dresselhaus spin-orbit couplings are slightly different. The spin Seebeck coefficient can be reduced by increasing temperature and disorder.

  2. Spin Seebeck effect through antiferromagnetic NiO

    NASA Astrophysics Data System (ADS)

    Prakash, Arati; Brangham, Jack; Yang, Fengyuan; Heremans, Joseph P.

    2016-07-01

    We report temperature-dependent spin Seebeck measurements on Pt/YIG bilayers and Pt/NiO/YIG trilayers, where YIG (yttrium iron garnet, Y3F e5O12 ) is an insulating ferrimagnet and NiO is an antiferromagnet at low temperatures. The thickness of the NiO layer is varied from 0 to 10 nm. In the Pt/YIG bilayers, the temperature gradient applied to the YIG stimulates dynamic spin injection into the Pt, which generates an inverse spin Hall voltage in the Pt. The presence of a NiO layer dampens the spin injection exponentially with a decay length of 2 ± 0.6 nm at 180 K. The decay length increases with temperature and shows a maximum of 5.5 ± 0.8 nm at 360 K. The temperature dependence of the amplitude of the spin Seebeck signal without NiO shows a broad maximum of 6.5 ± 0.5 μV/K at 20 K. In the presence of NiO, the maximum shifts sharply to higher temperatures, likely correlated to the increase in decay length. This implies that NiO is most transparent to magnon propagation near the paramagnet-antiferromagnet transition. We do not see the enhancement in spin current driven into Pt reported in other papers when 1-2 nm NiO layers are sandwiched between Pt and YIG.

  3. Enhancement of Seebeck Coefficient in Bi Nanowires by Electric Field Effect

    NASA Astrophysics Data System (ADS)

    Komine, Takashi; Aono, Tomosuke; Nabatame, Yuta; Murata, Masayuki; Hasegawa, Yasuhiro

    2016-03-01

    In this study, we investigated the electric field effect on the transport properties of a Bi nanowire. These effects were modeled by a surface potential. The electron states of Bi nanowires were numerically analyzed by effective mass equations at the T-point and L-point taking into account surface potential due to an external electric field. The Seebeck coefficients of Bi nanowires were calculated by using the Boltzmann equation with a constant relaxation time. It was found that the Seebeck coefficients increased when the sign of the surface potential parameter was negative. In particular, when the surface potential parameter was -1 eV and the skin depth was 10 nm in a 20-nm-diameter nanowire, the maximum absolute value of the Seebeck coefficient was larger than 1 mV/K, which was greatly improved compared to that without an external electric field.

  4. Nernst and Seebeck effects in HgTe/CdTe topological insulator

    NASA Astrophysics Data System (ADS)

    Zhang, Yuan; Song, Juntao; Li, Yu-Xian

    2015-03-01

    The Seebeck and Nernst effects in HgTe/CdTe quantum wells are studied using the tight-binding Hamiltonian and the nonequilibrium Green's function method. The Seebeck coefficient, Sc, and the Nernst coefficient, Nc, oscillate as a function of EF, where EF is the Fermi energy. The Seebeck coefficient shows peaks when the Fermi energy crosses the discrete transverse channels, and the height of the nth peak of the Sc is [ln2 /(1/2 +|n |)] for EF > 0. For the case EF < 0, the values of the peaks are negative, but the absolute values of the first five peaks are the same as those for EF > 0. The 6th peak of Sc reaches the value [ln2 /1.35 ] due to a higher density of states. When a magnetic field is applied, the Nernst coefficient appears. However, the values of the peaks for Nc are all positive. For a weak magnetic field, the temperature suppresses the oscillation of the Seebeck and Nernst coefficients but increases their magnitude. For a large magnetic field, because of the highly degenerate Landau levels, the peaks of the Seebeck coefficient at position EF=-12 , 10 , 28 meV , and Nernst coefficient at EF=-7 , 10 meV are robust against the temperature.

  5. Photo-Seebeck effect in tetragonal PbO single crystals

    SciTech Connect

    Mondal, P. S.; Okazaki, R.; Taniguchi, H.; Terasaki, I.

    2013-11-07

    We report the observation of photo-Seebeck effect in tetragonal PbO crystals. The photo-induced carriers contribute to the transport phenomena, and consequently the electrical conductivity increases and the Seebeck coefficient decreases with increasing photon flux density. A parallel-circuit model is used to evaluate the actual contributions of photo-excited carriers from the measured transport data. The photo-induced carrier concentration estimated from the Seebeck coefficient increases almost linearly with increasing photon flux density, indicating a successful photo-doping effect on the thermoelectric property. The mobility decreases by illumination but the reduction rate strongly depends on the illuminated photon energy. Possible mechanisms of such photon-energy-dependent mobility are discussed.

  6. Separation of spin Seebeck effect and anomalous Nernst effect in Co/Cu/YIG

    SciTech Connect

    Tian, Dai; Li, Yufan; Qu, D.; Chien, C. L.; Jin, Xiaofeng

    2015-05-25

    The spin Seebeck effect (SSE) and Anomalous Nernst effect (ANE) have been observed in Co/Cu/YIG (yttrium iron garnet) multi-layer structure, where the ferromagnetic insulator YIG acts as the pure spin injector and the ferromagnetic metal Co layer acts as the spin current detector. With the insertion of 5 nm Cu layer, the two ferromagnetic layers are decoupled, thus allowing unambiguous separation of the SSE and ANE contributions under the same experimental conditions in the same sample.

  7. Giant Seebeck effect in Ge-doped SnSe

    PubMed Central

    Gharsallah, M.; Serrano-Sánchez, F.; Nemes, N. M.; Mompeán, F. J.; Martínez, J. L.; Fernández-Díaz, M. T.; Elhalouani, F.; Alonso, J. A.

    2016-01-01

    Thermoelectric materials may contribute in the near future as new alternative sources of sustainable energy. Unprecedented thermoelectric properties in p-type SnSe single crystals have been recently reported, accompanied by extremely low thermal conductivity in polycrystalline samples. In order to enhance thermoelectric efficiency through proper tuning of this material we report a full structural characterization and evaluation of the thermoelectric properties of novel Ge-doped SnSe prepared by a straightforward arc-melting method, which yields nanostructured polycrystalline samples. Ge does not dope the system in the sense of donating carriers, yet the electrical properties show a semiconductor behavior with resistivity values higher than that of the parent compound, as a consequence of nanostructuration, whereas the Seebeck coefficient is higher and thermal conductivity lower, favorable to a better ZT figure of merit. PMID:27251233

  8. Giant Seebeck effect in Ge-doped SnSe.

    PubMed

    Gharsallah, M; Serrano-Sánchez, F; Nemes, N M; Mompeán, F J; Martínez, J L; Fernández-Díaz, M T; Elhalouani, F; Alonso, J A

    2016-01-01

    Thermoelectric materials may contribute in the near future as new alternative sources of sustainable energy. Unprecedented thermoelectric properties in p-type SnSe single crystals have been recently reported, accompanied by extremely low thermal conductivity in polycrystalline samples. In order to enhance thermoelectric efficiency through proper tuning of this material we report a full structural characterization and evaluation of the thermoelectric properties of novel Ge-doped SnSe prepared by a straightforward arc-melting method, which yields nanostructured polycrystalline samples. Ge does not dope the system in the sense of donating carriers, yet the electrical properties show a semiconductor behavior with resistivity values higher than that of the parent compound, as a consequence of nanostructuration, whereas the Seebeck coefficient is higher and thermal conductivity lower, favorable to a better ZT figure of merit. PMID:27251233

  9. Giant Seebeck effect in Ge-doped SnSe

    NASA Astrophysics Data System (ADS)

    Gharsallah, M.; Serrano-Sánchez, F.; Nemes, N. M.; Mompeán, F. J.; Martínez, J. L.; Fernández-Díaz, M. T.; Elhalouani, F.; Alonso, J. A.

    2016-06-01

    Thermoelectric materials may contribute in the near future as new alternative sources of sustainable energy. Unprecedented thermoelectric properties in p-type SnSe single crystals have been recently reported, accompanied by extremely low thermal conductivity in polycrystalline samples. In order to enhance thermoelectric efficiency through proper tuning of this material we report a full structural characterization and evaluation of the thermoelectric properties of novel Ge-doped SnSe prepared by a straightforward arc-melting method, which yields nanostructured polycrystalline samples. Ge does not dope the system in the sense of donating carriers, yet the electrical properties show a semiconductor behavior with resistivity values higher than that of the parent compound, as a consequence of nanostructuration, whereas the Seebeck coefficient is higher and thermal conductivity lower, favorable to a better ZT figure of merit.

  10. Absence of anomalous Nernst effect in spin Seebeck effect of Pt/YIG

    NASA Astrophysics Data System (ADS)

    Miao, B. F.; Huang, S. Y.; Qu, D.; Chien, C. L.

    2016-01-01

    The Pt/YIG structure has been widely used to study spin Seebeck effect (SSE), inverse spin Hall effect, and other pure spin current phenomena. However, the magnetic proximity effect in Pt when in contact with YIG, and the potential anomalous Nernst effect (ANE) may compromise the spin current phenomena in Pt/YIG. By inserting a Cu layer of various thicknesses between Pt and YIG, we have separated the signals from the SSE and that of the ANE. It is demonstrated that the thermal voltage in Pt/YIG mainly comes from spin current due to the longitudinal SSE with negligible contribution from the ANE.

  11. Nernst and Seebeck effects in HgTe/CdTe topological insulator

    SciTech Connect

    Zhang, Yuan; Song, Juntao; Li, Yu-Xian

    2015-03-28

    The Seebeck and Nernst effects in HgTe/CdTe quantum wells are studied using the tight-binding Hamiltonian and the nonequilibrium Green's function method. The Seebeck coefficient, S{sub c}, and the Nernst coefficient, N{sub c}, oscillate as a function of E{sub F}, where E{sub F} is the Fermi energy. The Seebeck coefficient shows peaks when the Fermi energy crosses the discrete transverse channels, and the height of the nth peak of the S{sub c} is [ln2/(1/2 +|n|)] for E{sub F} > 0. For the case E{sub F} < 0, the values of the peaks are negative, but the absolute values of the first five peaks are the same as those for E{sub F} > 0. The 6th peak of S{sub c} reaches the value [ln2/1.35] due to a higher density of states. When a magnetic field is applied, the Nernst coefficient appears. However, the values of the peaks for N{sub c} are all positive. For a weak magnetic field, the temperature suppresses the oscillation of the Seebeck and Nernst coefficients but increases their magnitude. For a large magnetic field, because of the highly degenerate Landau levels, the peaks of the Seebeck coefficient at position E{sub F}=−12, 10, 28meV, and Nernst coefficient at E{sub F}=−7, 10meV are robust against the temperature.

  12. Extracting the effective mass of electrons in transparent conductive oxide thin films using Seebeck coefficient

    SciTech Connect

    Wang, Yaqin; Zhu, Junhao; Tang, Wu

    2014-05-26

    A method is proposed that combines Seebeck coefficient and carrier concentration to determine the electron effective mass of transparent conductive oxide (TCO) thin films. Experiments were conducted to test the validity of this approach on the transparent conductive Ga-doped ZnO thin films deposited by magnetron sputtering. An evident agreement of the calculated electron effective mass of the films is observed between the proposed approach and the previous studies. Besides, the optical carrier concentration and mobility derived from the calculated electron effective mass and spectroscopic ellipsometry using a complex dielectric function are consistent with those from direct Hall-effect measurement. The agreements suggest that Seebeck coefficient can serve as an alternative tool for extracting the effective mass of electrons in TCO films.

  13. On/off switching of bit readout in bias-enhanced tunnel magneto-Seebeck effect.

    PubMed

    Boehnke, Alexander; Milnikel, Marius; von der Ehe, Marvin; Franz, Christian; Zbarsky, Vladyslav; Czerner, Michael; Rott, Karsten; Thomas, Andy; Heiliger, Christian; Reiss, Günter; Münzenberg, Markus

    2015-01-01

    Thermoelectric effects in magnetic tunnel junctions are promising to serve as the basis for logic devices or memories in a "green" information technology. However, up to now the readout contrast achieved with Seebeck effects was magnitudes smaller compared to the well-established tunnel magnetoresistance effect. Here, we resolve this problem by demonstrating that the tunnel magneto-Seebeck effect (TMS) in CoFeB/MgO/CoFeB tunnel junctions can be switched on to a logic "1" state and off to "0" by simply changing the magnetic state of the CoFeB electrodes. This new functionality is achieved by combining a thermal gradient and an electric field. Our results show that the signal crosses zero and can be adjusted by tuning a bias voltage that is applied between the electrodes of the junction; hence, the name of the effect is bias-enhanced tunnel magneto-Seebeck effect (bTMS). Via the spin- and energy-dependent transmission of electrons in the junction, the bTMS effect can be configured using the bias voltage with much higher control than the tunnel magnetoresistance and even completely suppressed for only one magnetic configuration. Moreover, our measurements are a step towards the experimental realization of high TMS ratios without additional bias voltage, which are predicted for specific Co-Fe compositions. PMID:25755010

  14. On/off switching of bit readout in bias-enhanced tunnel magneto-Seebeck effect

    PubMed Central

    Boehnke, Alexander; Milnikel, Marius; von der Ehe, Marvin; Franz, Christian; Zbarsky, Vladyslav; Czerner, Michael; Rott, Karsten; Thomas, Andy; Heiliger, Christian; Reiss, Günter; Münzenberg, Markus

    2015-01-01

    Thermoelectric effects in magnetic tunnel junctions are promising to serve as the basis for logic devices or memories in a ”green” information technology. However, up to now the readout contrast achieved with Seebeck effects was magnitudes smaller compared to the well-established tunnel magnetoresistance effect. Here, we resolve this problem by demonstrating that the tunnel magneto-Seebeck effect (TMS) in CoFeB/MgO/CoFeB tunnel junctions can be switched on to a logic “1” state and off to “0” by simply changing the magnetic state of the CoFeB electrodes. This new functionality is achieved by combining a thermal gradient and an electric field. Our results show that the signal crosses zero and can be adjusted by tuning a bias voltage that is applied between the electrodes of the junction; hence, the name of the effect is bias-enhanced tunnel magneto-Seebeck effect (bTMS). Via the spin- and energy-dependent transmission of electrons in the junction, the bTMS effect can be configured using the bias voltage with much higher control than the tunnel magnetoresistance and even completely suppressed for only one magnetic configuration. Moreover, our measurements are a step towards the experimental realization of high TMS ratios without additional bias voltage, which are predicted for specific Co-Fe compositions. PMID:25755010

  15. On/off switching of bit readout in bias-enhanced tunnel magneto-Seebeck effect

    NASA Astrophysics Data System (ADS)

    Boehnke, Alexander; Milnikel, Marius; von der Ehe, Marvin; Franz, Christian; Zbarsky, Vladyslav; Czerner, Michael; Rott, Karsten; Thomas, Andy; Heiliger, Christian; Reiss, Günter; Münzenberg, Markus

    2015-03-01

    Thermoelectric effects in magnetic tunnel junctions are promising to serve as the basis for logic devices or memories in a ''green'' information technology. However, up to now the readout contrast achieved with Seebeck effects was magnitudes smaller compared to the well-established tunnel magnetoresistance effect. Here, we resolve this problem by demonstrating that the tunnel magneto-Seebeck effect (TMS) in CoFeB/MgO/CoFeB tunnel junctions can be switched on to a logic ``1'' state and off to ``0'' by simply changing the magnetic state of the CoFeB electrodes. This new functionality is achieved by combining a thermal gradient and an electric field. Our results show that the signal crosses zero and can be adjusted by tuning a bias voltage that is applied between the electrodes of the junction; hence, the name of the effect is bias-enhanced tunnel magneto-Seebeck effect (bTMS). Via the spin- and energy-dependent transmission of electrons in the junction, the bTMS effect can be configured using the bias voltage with much higher control than the tunnel magnetoresistance and even completely suppressed for only one magnetic configuration. Moreover, our measurements are a step towards the experimental realization of high TMS ratios without additional bias voltage, which are predicted for specific Co-Fe compositions.

  16. Comparison of the magneto-Peltier and magneto-Seebeck effects in magnetic tunnel junctions

    NASA Astrophysics Data System (ADS)

    Shan, J.; Dejene, F. K.; Leutenantsmeyer, J. C.; Flipse, J.; Münzenberg, M.; van Wees, B. J.

    2015-07-01

    Understanding heat generation and transport processes in a magnetic tunnel junction (MTJ) is a significant step towards improving its application in current memory devices. Recent work has experimentally demonstrated the magneto-Seebeck effect in MTJs, where the Seebeck coefficient of the junction varies as the magnetic configuration changes from a parallel (P) to an antiparallel (AP) configuration. Here we report a study on its reciprocal effect, the magneto-Peltier effect, where the heat flow carried by the tunneling electrons is altered by changing the magnetic configuration of the MTJ. The magneto-Peltier signal that reflects the change in the temperature difference across the junction between the P and AP configurations scales linearly with the applied current in the small bias but is greatly enhanced in the large-bias regime, due to higher-order Joule heating mechanisms. By carefully extracting the linear response which reflects the magneto-Peltier effect, and comparing it with the magneto-Seebeck measurements performed on the same device, we observe results consistent with Onsager reciprocity. We estimate a magneto-Peltier coefficient of 13.4 mV in the linear regime using a three-dimensional thermoelectric model. Our result opens up the possibility of programmable thermoelectric devices based on the Peltier effect in MTJs.

  17. Charge Transport in Thin Organic Semiconducting Films: Seebeck and Field Effect Studies

    NASA Astrophysics Data System (ADS)

    Böhm, W.; Fritz, T.; Leo, K.

    1997-03-01

    We have investigated the charge transport properties of vapor-deposited thin organic films, using the Seebeck effect for determining conduction type and Fermi energy and the field effect to measure mobility and total charge carrier density. We show that the combination of both techniques gives a complete picture of the electrical properties of the films. Wir untersuchen den Ladungsträgertransport in aufgedampften dünnen organischen Schichten, wobei der Seebeck-Effekt zur Bestimmung des Leitfähigkeitstyps und der Lage des Ferminiveaus und der Feldeffekt zur Bestimmung der Leitfähigkeit und der gesamten Ladungsträgerdichte benutzt wird. Es wird gezeigt, daß durch die Kombination beider Methoden ein geschlossenes Bild der elektrischen Eigenschaften erhalten wird.

  18. Magnon spin-current theory for the longitudinal spin-Seebeck effect

    NASA Astrophysics Data System (ADS)

    Rezende, S. M.; Rodríguez-Suárez, R. L.; Cunha, R. O.; Rodrigues, A. R.; Machado, F. L. A.; Fonseca Guerra, G. A.; Lopez Ortiz, J. C.; Azevedo, A.

    2014-01-01

    We present a theoretical model for the longitudinal spin-Seebeck effect (LSSE) in bilayers made of a ferromagnetic insulator (FMI), such as yttrium iron garnet (YIG), and a normal metal (NM), such as platinum (Pt), that relies on the bulk magnon spin current created by the temperature gradient across the thickness of the FMI. We show that the spin current pumped into the NM layer by the magnon accumulation in the FMI provides continuity of the spin current at the FMI/NM interface and is essential for the existence of the longitudinal spin-Seebeck effect. The results of the theory are in good agreement with experimental data for the variation of the LSSE with the sample temperature and with the FMI layer thickness in YIG/Pt bilayers.

  19. Spin-resolved Fano resonances induced large spin Seebeck effects in graphene-carbon-chain junctions

    SciTech Connect

    Liu, Yu-Shen; Zhang, Xue; Feng, Jin-Fu; Wang, Xue-Feng

    2014-06-16

    We propose a high-efficiency thermospin device constructed by a carbon atomic chain sandwiched between two ferromagnetic (FM) zigzag graphene nanoribbon electrodes. In the low-temperature regime, the magnitude of the spin figure of merit is nearly equal to that of the corresponding charge figure of merit. This is attributed to the appearances of spin-resolved Fano resonances in the linear conductance spectrum resulting from the quantum interference effects between the localized states and the expanded states. The spin-dependent Seebeck effect is obviously enhanced near these Fano resonances with the same spin index; meanwhile, the Seebeck effect of the other spin component has a smaller value due to the smooth changing of the linear conductance with the spin index. Thus, a large spin Seebeck effect is achieved, and the magnitude of the spin figure of merit can reach 1.2 at T = 25 K. Our results indicate that the FM graphene-carbon-chain junctions can be used to design the high-efficiency thermospin devices.

  20. The Third Way of Thermal-Electric Conversion beyond Seebeck and Pyroelectric Effects

    SciTech Connect

    Ren, Jie

    2014-02-14

    Thermal-electric conversion is crucial for smart energy control and harvesting, such as thermal sensing and waste heat recovering. So far, people are aware of only two ways of direct thermal-electric conversion, Seebeck and pyroelectric effects, each with distinct working conditions and limitations. Here, we report the third way of thermal-electric conversion beyond Seebeck and pyroelectric effects. In contrast to Seebeck effect that requires spatial temperature difference, the-third-way converts the time-dependent ambient temperature fluctuation into electricity, similar to the behavior of pyroelectricity. However, the-third-way is also distinct from pyroelectric effect in the sense that it does not require polar materials but applies to general conducting systems. We demonstrate that the-third-way results from the temperature-fluctuation-induced dynamical charge redistribution. It is a consequence of the fundamental nonequilibrium thermodynamics and has a deep connection to the topological phase in quantum mechanics. Our findings expand our knowledge and provide new means of thermal-electric energy harvesting.

  1. Observation of inverse spin Hall effect in ferromagnetic FePt alloys using spin Seebeck effect

    SciTech Connect

    Seki, Takeshi Takanashi, Koki; Uchida, Ken-ichi; Kikkawa, Takashi; Qiu, Zhiyong; Saitoh, Eiji

    2015-08-31

    We experimentally observed the inverse spin Hall effect (ISHE) of ferromagnetic FePt alloys. Spin Seebeck effect due to the temperature gradient generated the spin current (J{sub s}) in the FePt|Y{sub 3}Fe{sub 5}O{sub 12} (YIG) structure, and J{sub s} was injected from YIG to FePt and converted to the charge current through ISHE of FePt. The significant difference in magnetization switching fields for FePt and YIG led to the clear separation of the voltage of ISHE from that of anomalous Nernst effect in FePt. We also investigated the effect of ordering of FePt crystal structure on the magnitude of ISHE voltage in FePt.

  2. A spin-Seebeck diode with a negative differential spin-Seebeck effect in a hydrogen-terminated zigzag silicene nanoribbon heterojunction.

    PubMed

    Fu, Hua-Hua; Gu, Lei; Wu, Dan-Dan

    2016-05-14

    The spin-Seebeck effect (SSE), the central topic of spin caloritronics, provides a new direction for future low power consumption technology. To realize device applications of SSE, a spin-Seebeck diode (SSD) with a negative differential SSE is very desirable. To this end, we constructed a spin caloritronics device that was composed of a ferromagnetic double-single-hydrogen-terminated zigzag silicene nanoribbon (ZSiNR-H2-H) and an antiferromagnetic double-double-hydrogen-terminated zigzag silicene nanoribbon (ZSiNR-H2-H2). By using ab initio calculations combined with nonequilibrium Green's function technique, we found that thermally driven spin current through the heterojunction featured the SSD effect and negative differential SSE. The former originates from the asymmetrical thermal-driven conducting electrons and holes, and the latter ascribes to the thermal spin compensation effect. Their physical mechanisms are much different from the previous ones mainly relying on the spin-wave excitations in the interface between metals and magnetic insulators, supporting our study that puts forward a new route to realize the SSD with a negative differential SSE. PMID:27098900

  3. Seebeck coefficient of one electron

    SciTech Connect

    Durrani, Zahid A. K.

    2014-03-07

    The Seebeck coefficient of one electron, driven thermally into a semiconductor single-electron box, is investigated theoretically. With a finite temperature difference ΔT between the source and charging island, a single electron can charge the island in equilibrium, directly generating a Seebeck effect. Seebeck coefficients for small and finite ΔT are calculated and a thermally driven Coulomb staircase is predicted. Single-electron Seebeck oscillations occur with increasing ΔT, as one electron at a time charges the box. A method is proposed for experimental verification of these effects.

  4. Low-Temperature Seebeck Coefficients for Polaron-Driven Thermoelectric Effect in Organic Polymers.

    PubMed

    de Oliveira Neto, Pedro Henrique; da Silva Filho, Demétrio A; Roncaratti, Luiz F; Acioli, Paulo H; E Silva, Geraldo Magela

    2016-07-14

    We report the results of electronic structure coupled to molecular dynamics simulations on organic polymers subject to a temperature gradient at low-temperature regimes. The temperature gradient is introduced using a Langevin-type dynamics corrected for quantum effects, which are very important in these systems. Under this condition we were able to determine that in these no-impurity systems the Seebeck coefficient is in the range of 1-3 μV/K. These results are in good agreement with reported experimental results under the same low-temperature conditions. PMID:26886243

  5. Spin-dependent Seebeck effect and spin caloritronics in magnetic graphene

    NASA Astrophysics Data System (ADS)

    Rameshti, Babak Zare; Moghaddam, Ali G.

    2015-04-01

    We investigate the spin-dependent thermoelectric effects in magnetic graphene in both diffusive and ballistic regimes. Employing the Boltzmann and Landauer formalisms we calculate the spin and charge Seebeck coefficients (thermopower) in magnetic graphene varying the spin splitting, temperature, and doping of the junction. It is found that while in normal graphene the temperature gradient drives a charge current, in the case of magnetic graphene a significant spin current is also established. In particular we show that in the undoped magnetic graphene in which different spin carriers belong to conduction and valence bands, a pure spin current is driven by the temperature gradient. In addition it is revealed that profound thermoelectric effects can be achieved at intermediate easily accessible temperatures when the thermal energy is comparable with Fermi energy kBT ≲μ . By further investigation of the spin-dependent Seebeck effect and a significantly large figure of merit for spin thermopower ZspT , we suggest magnetic graphene as a promising material for spin-caloritronics studies and applications.

  6. Enhanced spin Seebeck effect in a germanene p-n junction

    SciTech Connect

    Zheng, Jun; Chi, Feng; Guo, Yong

    2014-12-28

    Spin Seebeck effect in a germanene p-n junction is studied by using the nonequilibrium Green's function method combined with the tight-binding Hamiltonian. We find that the thermal bias ΔT can generate spin thermopower when a local exchange field is applied on one edge of the germanene nano-ribbon. The magnitude of the spin thermopower can be modulated by the potential drop across the two terminals of the p-n junction. When the value of the potential drop is smaller than the spin-orbit interaction strength, the spin thermopower is enhanced by two orders of magnitude larger as compared to the case of zero p-n voltage. Optimal temperature corresponding to maximum spin thermopower is insensitive to the potential drop. In the p-n region, maximum spin thermopower can be obtained at relatively higher temperatures. When the value of the potential drop is larger than that of the spin-orbit interaction, however, the spin Seebeck effect decays rapidly with increasing potential drop or temperature. By optimizing the structure parameters, the magnitude of the spin thermopower can be remarkably enhanced due to the coexistence of the exchange field and the potential drop.

  7. Asymmetric and Negative Differential Thermal Spin Effect at Magnetic Interfaces: Towards Spin Seebeck Diodes and Transistors

    NASA Astrophysics Data System (ADS)

    Ren, Jie; Zhu, Jian-Xin

    2014-03-01

    We study the nonequilibrium thermal-spin transport across metal-magnetic insulator interfaces. The transport is assisted by the exchange interaction between conduction electrons in the metal and localized spins in the magnetic insulator. We predict the rectification and negative differential spin Seebeck effect (SSE), that is, reversing the temperature bias is able to give asymmetric spin currents and increasing temperature bias could give an anomalously decreasing spin current. We resolve their microscopic mechanism as a consequence of the energy-dependent electronic DOS in the metal. The rectification of spin Peltier effect is also discussed. We then study the asymmetric and negative differential magnon tunneling driven by temperature bias. We show that the many-body magnon interaction that makes the magnonic spectrum temperature-dependent is the crucial factor for the emergence of rectification and negative differential SSEs in magnon tunneling junctions. We show that these asymmetric and negative differential SSEs are relevant for building magnon and spin Seebeck diodes and transistors, which could play important roles in controlling information and energy in functional devices. Supported by the National Nuclear Security Administration of the US DOE at LANL under Contract No. DE-AC52-06NA25396.

  8. Spin Seebeck Effect vs. Anomalous Nernst Effect in Ta/CoFeB /Ta Structures

    NASA Astrophysics Data System (ADS)

    Yang, Bowen; Xu, Yadong; Schneider, Mike; Shi, Jing; Univ of California-Riverside Team; Everspin Technologies Inc. Team

    2014-03-01

    We have studied the spin Seebeck effect (SSE) and anomalous Nernst effect (ANE) in a vertical trilayer structure under a vertical temperature gradient. The structure consists of a 3nm CoFeB layer sandwiched by β-phase tantalum (Ta) layers. The samples are deposited by magnetron sputtering. The existence of Ta β-phase is verified by the resistivity and its negative temperature coefficient of resistance(TCR). Under a fixed vertical temperature gradient, the measured transverse thermoelectric voltage is linearly proportional to the total sample resistance when the Ta thickness exceeds 2 nm, which can be explained by a shunting resistor model. When the Ta thickness is below 2 nm, the voltage deviates from the linear resistance dependence and merges to the ANE voltage of the CoFeB single layer, due to a weakened inverse spin Hall effect (ISHE) in Ta thinner than the spin diffusion length. In the linear regime, the slope contains both a varying SSE and a fixed ANE responses, thus the SSE contribution could be quantitatively separated out from the ANE of CoFeB. Our results indicate a large SSE from the β-phase Ta due to its large Spin Hall Angle. This work was supported by CNN/DMEA and DOE.

  9. Electric gating induced bandgaps and enhanced Seebeck effect in zigzag bilayer graphene ribbons

    NASA Astrophysics Data System (ADS)

    Vu, Thanh-Tra; Tran, Van-Truong

    2016-08-01

    We theoretically investigate the effect of a transverse electric field generated by side gates and a vertical electric field generated by top/back gates on energy bands and transport properties of zigzag bilayer graphene ribbons (Bernal stacking). Using atomistic tight binding calculations and Green’s function formalism we demonstrate that a bandgap is opened when either field is applied and even enlarged under simultaneous influence of the two fields. Interestingly, although vertical electric fields are widely used to control the bandgap in bilayer graphene, here we show that transverse fields exhibit a more positive effect in terms of modulating a larger range of bandgap and retaining good electrical conductance. The Seebeck effect is also demonstrated to be enhanced strongly—by about 13 times for a zigzag bilayer graphene ribbon with 16 chain lines. These results may motivate new designs of devices made of bilayer graphene ribbons using electric gates.

  10. Investigation of the magnetic properties of insulating thin films using the longitudinal spin Seebeck effect

    SciTech Connect

    Kehlberger, A. Jakob, G.; Kläui, M.; Onbasli, M. C.; Kim, D. H.; Ross, C. A.

    2014-05-07

    The longitudinal spin Seebeck effect is used as a detector for the magnetic properties and switching characteristics of magnetic thin insulating films. We use a 300 nm and a 20 nm thick Yttrium Iron Garnet (YIG, Y{sub 3}Fe{sub 5}O{sub 12}) film prepared by pulsed laser deposition and afterwards coated by platinum for the detection of the thermally excited magnons by the inverse spin Hall effect. The inverse spin Hall signals reveal a magnetic uniaxial anisotropy along the direction of the platinum stripe in the thicker film. For the thin film we find a more isotropic behavior, which is complementarily observed using the magnetoresistance occurring at the platinum/YIG interface. We explain our results on the basis of x-ray diffraction data, which reveal a miscut of the substrate and film surface and an expansion of the YIG lattice. Both findings favor a growth-induced magnetic anisotropy that we observe.

  11. Seebeck effect influence on joule heat evolution in electrically conductive silicate materials

    NASA Astrophysics Data System (ADS)

    Fiala, Lukáš; Medved, Igor; Maděra, Jiří; Černý, Robert

    2016-07-01

    In general, silicate building materials are non-conductive matters that are not able to evolve heat when they are subjected to an external voltage. However, the electrical conductivity can be increased by addition of electrically conductive admixtures in appropriate amount which leads to generation of conductive paths in materials matrix. Such enhanced materials can evolve Joule heat and are utilizable as a core of self-heating or snow-melting systems. In this paper, Joule heat evolution together with Seebeck effect in electrically conductive silicate materials was taken into consideration and the model based on heat equation with included influence of DC electric field was proposed. Besides, a modeling example of heating element was carried out on FEM basis and time development of temperature in chosen surface points was expressed in order to declare ability of such system to be applicable.

  12. High spin-filter efficiency and Seebeck effect through spin-crossover iron-benzene complex

    NASA Astrophysics Data System (ADS)

    Yan, Qiang; Zhou, Liping; Cheng, Jue-Fei; Wen, Zhongqian; Han, Qin; Wang, Xue-Feng

    2016-04-01

    Electronic structures and coherent quantum transport properties are explored for spin-crossover molecule iron-benzene Fe(Bz)2 using density functional theory combined with non-equilibrium Green's function. High- and low-spin states are investigated for two different lead-molecule junctions. It is found that the asymmetrical T-shaped contact junction in the high-spin state behaves as an efficient spin filter while it has a smaller conductivity than that in the low-spin state. Large spin Seebeck effect is also observed in asymmetrical T-shaped junction. Spin-polarized properties are absent in the symmetrical H-shaped junction. These findings strongly suggest that both the electronic and contact configurations play significant roles in molecular devices and metal-benzene complexes are promising materials for spintronics and thermo-spintronics.

  13. High spin-filter efficiency and Seebeck effect through spin-crossover iron-benzene complex.

    PubMed

    Yan, Qiang; Zhou, Liping; Cheng, Jue-Fei; Wen, Zhongqian; Han, Qin; Wang, Xue-Feng

    2016-04-21

    Electronic structures and coherent quantum transport properties are explored for spin-crossover molecule iron-benzene Fe(Bz)2 using density functional theory combined with non-equilibrium Green's function. High- and low-spin states are investigated for two different lead-molecule junctions. It is found that the asymmetrical T-shaped contact junction in the high-spin state behaves as an efficient spin filter while it has a smaller conductivity than that in the low-spin state. Large spin Seebeck effect is also observed in asymmetrical T-shaped junction. Spin-polarized properties are absent in the symmetrical H-shaped junction. These findings strongly suggest that both the electronic and contact configurations play significant roles in molecular devices and metal-benzene complexes are promising materials for spintronics and thermo-spintronics. PMID:27389217

  14. Hot-Carrier Seebeck Effect: Diffusion and Remote Detection of Hot Carriers in Graphene.

    PubMed

    Sierra, Juan F; Neumann, Ingmar; Costache, Marius V; Valenzuela, Sergio O

    2015-06-10

    We investigate hot carrier propagation across graphene using an electrical nonlocal injection/detection method. The device consists of a monolayer graphene flake contacted by multiple metal leads. Using two remote leads for electrical heating, we generate a carrier temperature gradient that results in a measurable thermoelectric voltage V(NL) across the remaining (detector) leads. Due to the nonlocal character of the measurement, V(NL) is exclusively due to the Seebeck effect. Remarkably, a departure from the ordinary relationship between Joule power P and V(NL), V(NL) ∼ P, becomes readily apparent at low temperatures, representing a fingerprint of hot-carrier dominated thermoelectricity. By studying V(NL) as a function of bias, we directly determine the carrier temperature and the characteristic cooling length for hot-carrier propagation, which are key parameters for a variety of new applications that rely on hot-carrier transport. PMID:25950746

  15. Bose-Einstein condensation of magnons pumped by the bulk spin Seebeck effect

    NASA Astrophysics Data System (ADS)

    Tserkovnyak, Yaroslav; Bender, Scott A.; Duine, Rembert A.; Flebus, Benedetta

    2016-03-01

    We propose inducing Bose-Einstein condensation of magnons in a magnetic insulator by a heat flow oriented toward its boundary. At a critical heat flux, the oversaturated thermal gas of magnons accumulated at the boundary precipitates the condensate, which then grows gradually as the thermal bias is dialed up further. The thermal magnons thus pumped by the magnonic bulk (spin) Seebeck effect must generally overcome both the local Gilbert damping associated with the coherent magnetic dynamics as well as the radiative spin-wave losses toward the magnetic bulk, in order to achieve the threshold of condensation. We quantitatively estimate the requisite bias in the case of the ferrimagnetic yttrium iron garnet, discuss different physical regimes of condensation, and contrast it with the competing (so-called Doppler-shift) bulk instability.

  16. Robust longitudinal spin-Seebeck effect in Bi-YIG thin films

    NASA Astrophysics Data System (ADS)

    Siegel, Gene; Prestgard, Megan Campbell; Teng, Shiang; Tiwari, Ashutosh

    2014-03-01

    In recent years, the coupling of magnetic insulators (bismuth-doped yttrium iron garnet, Bi-YIG) with platinum has garnered significant interest in spintronics research due to applicability as spin-current-driven thermoelectric coatings. These coatings bridge the gap between spintronics technologies and thermoelectric materials, providing a novel means of transforming waste heat into electricity. However, there remain questions regarding the origins of the spin-Seebeck effect (SSE) as well as claims that observed effects are a manifestation of magnetic proximity effects, which would induce magnetic behavior in platinum. Herewith we provide support that the voltages observed in the Bi-YIG/Pt films are purely SSE voltages. We reaffirm claims that magnon transport theory provides an ample basis for explaining SSE behavior. Finally, we illustrate the advantages of pulsed-laser deposition, as these Bi-YIG films possess large SSE voltages (even in absence of an external magnetic field), as much as twice those of films fabricated via solution-based methods.

  17. Complete Suppression of Longitudinal Spin Seebeck Effect by Frozen Magnetization Dynamics in Y3Fe5O12

    NASA Astrophysics Data System (ADS)

    Kikkawa, Takashi; Uchida, Ken-ichi; Daimon, Shunsuke; Saitoh, Eiji

    2016-06-01

    The spin Seebeck effect (SSE) in a Pt-film/Y3Fe5O12 (YIG)-slab junction system has been investigated at low temperatures and under various magnetic fields in the longitudinal configuration. We found that, by increasing applied magnetic fields, the SSE signal gradually decreases and converges to zero without showing sign reversal. The complete field-induced suppression of the SSE is interpreted in terms of the effect of the Zeeman gap in magnon excitation.

  18. Observation of longitudinal spin-Seebeck effect in cobalt-ferrite epitaxial thin films

    SciTech Connect

    Niizeki, Tomohiko; Kikkawa, Takashi; Uchida, Ken-ichi; Oka, Mineto; Suzuki, Kazuya Z.; Yanagihara, Hideto; Kita, Eiji; Saitoh, Eiji

    2015-05-15

    The longitudinal spin-Seebeck effect (LSSE) has been investigated in cobalt ferrite (CFO), an exceptionally hard magnetic spinel ferrite. A bilayer of a polycrystalline Pt and an epitaxially-strained CFO(110) exhibiting an in-plane uniaxial anisotropy was prepared by reactive rf sputtering technique. Thermally generated spin voltage in the CFO layer was measured via the inverse spin-Hall effect in the Pt layer. External-magnetic-field (H) dependence of the LSSE voltage (V{sub LSSE}) in the Pt/CFO(110) sample with H ∥ [001] was found to exhibit a hysteresis loop with a high squareness ratio and high coercivity, while that with H∥[11{sup -}0] shows a nearly closed loop, reflecting the different anisotropies induced by the epitaxial strain. The magnitude of V{sub LSSE} has a linear relationship with the temperature difference (ΔT), giving the relatively large V{sub LSSE} /ΔT of about 3 μV/K for CFO(110) which was kept even at zero external field.

  19. Bulk magnon spin current theory for the longitudinal spin Seebeck effect

    NASA Astrophysics Data System (ADS)

    Rezende, S. M.; Rodríguez-Suárez, R. L.; Cunha, R. O.; López Ortiz, J. C.; Azevedo, A.

    2016-02-01

    The longitudinal spin Seebeck effect (LSSE) consists in the generation of a spin current parallel to a temperature gradient applied across the thickness of a bilayer made of a ferromagnetic insulator (FMI), such as yttrium iron garnet (YIG), and a metallic layer (ML) with strong spin orbit coupling, such as platinum. The LSSE is usually detected by a DC voltage generated along the ML due to the conversion of the spin current into a charge current perpendicular to the static magnetic field by means of the inverse spin Hall effect. Here we present a model for the LSSE that relies on the bulk magnon spin current created by the temperature gradient across the thickness of the FMI. We show that the spin current pumped into the metallic layer by the magnon accumulation in the FMI provides continuity of the spin current at the FMI/ML interface and is essential for the existence of the LSSE. The results of the theory are in good agreement with experimental LSSE data in YIG/Pt bilayers on the variation of the DC voltage with the sample temperature, with the FMI layer thickness and with the intensity of high magnetic fields.

  20. Tunneling Seebeck and Anomalous Nernst effects in three-dimensional topological insulators

    NASA Astrophysics Data System (ADS)

    Shen, Chenghao; Scharf, Benedikt; Matos-Abiague, Alex; Zutic, Igor

    We theoretically investigate the longitudinal (Seebeck) and transverse (Nernst) thermopowers generated by thermally-induced tunneling across a magnetic barrier on the surface of a three-dimensional insulator. As a manifestation of Klein tunneling, the tunneling Seebeck coefficient exhibits oscillatory behavior with respect to the barrier thickness. Moreover, in spite of the absence of a source of spin polarization (only the barrier is magnetic), the tunneling anomalous Nernst coefficient is not only finite but can even be much larger than its Seebeck counterpart. This work was supported by DFG Grant No. SCHA 1899/1-1 (B.S.), U.S. ONR Grant No. N000141310754 (B.S., A.M.-A.), U.S. DOE, Office of Science BES, under Award DE-SC0004890 (I.Z.).

  1. Enhanced spin Seebeck effect signal due to spin-momentum locked topological surface states.

    PubMed

    Jiang, Zilong; Chang, Cui-Zu; Masir, Massoud Ramezani; Tang, Chi; Xu, Yadong; Moodera, Jagadeesh S; MacDonald, Allan H; Shi, Jing

    2016-01-01

    Spin-momentum locking in protected surface states enables efficient electrical detection of magnon decay at a magnetic-insulator/topological-insulator heterojunction. Here we demonstrate this property using the spin Seebeck effect (SSE), that is, measuring the transverse thermoelectric response to a temperature gradient across a thin film of yttrium iron garnet, an insulating ferrimagnet, and forming a heterojunction with (BixSb1-x)2Te3, a topological insulator. The non-equilibrium magnon population established at the interface can decay in part by interactions of magnons with electrons near the Fermi energy of the topological insulator. When this decay channel is made active by tuning (BixSb1-x)2Te3 into a bulk insulator, a large electromotive force emerges in the direction perpendicular to the in-plane magnetization of yttrium iron garnet. The enhanced, tunable SSE which occurs when the Fermi level lies in the bulk gap offers unique advantages over the usual SSE in metals and therefore opens up exciting possibilities in spintronics. PMID:27142594

  2. Enhanced spin Seebeck effect signal due to spin-momentum locked topological surface states

    NASA Astrophysics Data System (ADS)

    Jiang, Zilong; Chang, Cui-Zu; Masir, Massoud Ramezani; Tang, Chi; Xu, Yadong; Moodera, Jagadeesh S.; MacDonald, Allan H.; Shi, Jing

    2016-05-01

    Spin-momentum locking in protected surface states enables efficient electrical detection of magnon decay at a magnetic-insulator/topological-insulator heterojunction. Here we demonstrate this property using the spin Seebeck effect (SSE), that is, measuring the transverse thermoelectric response to a temperature gradient across a thin film of yttrium iron garnet, an insulating ferrimagnet, and forming a heterojunction with (BixSb1-x)2Te3, a topological insulator. The non-equilibrium magnon population established at the interface can decay in part by interactions of magnons with electrons near the Fermi energy of the topological insulator. When this decay channel is made active by tuning (BixSb1-x)2Te3 into a bulk insulator, a large electromotive force emerges in the direction perpendicular to the in-plane magnetization of yttrium iron garnet. The enhanced, tunable SSE which occurs when the Fermi level lies in the bulk gap offers unique advantages over the usual SSE in metals and therefore opens up exciting possibilities in spintronics.

  3. Enhanced spin Seebeck effect signal due to spin-momentum locked topological surface states

    PubMed Central

    Jiang, Zilong; Chang, Cui-Zu; Masir, Massoud Ramezani; Tang, Chi; Xu, Yadong; Moodera, Jagadeesh S.; MacDonald, Allan H.; Shi, Jing

    2016-01-01

    Spin-momentum locking in protected surface states enables efficient electrical detection of magnon decay at a magnetic-insulator/topological-insulator heterojunction. Here we demonstrate this property using the spin Seebeck effect (SSE), that is, measuring the transverse thermoelectric response to a temperature gradient across a thin film of yttrium iron garnet, an insulating ferrimagnet, and forming a heterojunction with (BixSb1−x)2Te3, a topological insulator. The non-equilibrium magnon population established at the interface can decay in part by interactions of magnons with electrons near the Fermi energy of the topological insulator. When this decay channel is made active by tuning (BixSb1−x)2Te3 into a bulk insulator, a large electromotive force emerges in the direction perpendicular to the in-plane magnetization of yttrium iron garnet. The enhanced, tunable SSE which occurs when the Fermi level lies in the bulk gap offers unique advantages over the usual SSE in metals and therefore opens up exciting possibilities in spintronics. PMID:27142594

  4. Enhanced spin Seebeck effect signal due to spin-momentum locked topological surface states

    DOE PAGESBeta

    Jiang, Zilong; Chang, Cui -Zu; Masir, Massoud Ramezani; Tang, Chi; Xu, Yadong; Moodera, Jagadeesh S.; MacDonald, Allan H.; Shi, Jing

    2016-05-04

    Spin-momentum locking in protected surface states enables efficient electrical detection of magnon decay at a magnetic-insulator/topological-insulator heterojunction. Here we demonstrate this property using the spin Seebeck effect (SSE), that is, measuring the transverse thermoelectric response to a temperature gradient across a thin film of yttrium iron garnet, an insulating ferrimagnet, and forming a heterojunction with (BixSb1–x)2Te3, a topological insulator. The non-equilibrium magnon population established at the interface can decay in part by interactions of magnons with electrons near the Fermi energy of the topological insulator. When this decay channel is made active by tuning (BixSb1–x)2Te3 into a bulk insulator, amore » large electromotive force emerges in the direction perpendicular to the in-plane magnetization of yttrium iron garnet. Lastly, the enhanced, tunable SSE which occurs when the Fermi level lies in the bulk gap offers unique advantages over the usual SSE in metals and therefore opens up exciting possibilities in spintronics.« less

  5. Charge carrier effective mass and concentration derived from combination of Seebeck coefficient and Te125 NMR measurements in complex tellurides

    DOE PAGESBeta

    Levin, E. M.

    2016-06-27

    Thermoelectric materials utilize the Seebeck effect to convert heat to electrical energy. The Seebeck coefficient (thermopower), S, depends on the free (mobile) carrier concentration, n, and effective mass, m*, as S ~ m*/n2/3. The carrier concentration in tellurides can be derived from 125Te nuclear magnetic resonance (NMR) spin-lattice relaxation measurements. The NMR spin-lattice relaxation rate, 1/T1, depends on both n and m* as 1/T1~(m*)3/2n (within classical Maxwell-Boltzmann statistics) or as 1/T1~(m*)2n2/3 (within quantum Fermi-Dirac statistics), which challenges the correct determination of the carrier concentration in some materials by NMR. Here it is shown that the combination of the Seebeck coefficientmore » and 125Te NMR spin-lattice relaxation measurements in complex tellurides provides a unique opportunity to derive the carrier effective mass and then to calculate the carrier concentration. This approach was used to study AgxSbxGe50–2xTe50, well-known GeTe-based high-efficiency tellurium-antimony-germanium-silver thermoelectric materials, where the replacement of Ge by [Ag+Sb] results in significant enhancement of the Seebeck coefficient. Thus, values of both m* and n derived using this combination show that the enhancement of thermopower can be attributed primarily to an increase of the carrier effective mass and partially to a decrease of the carrier concentration when the [Ag+Sb] content increases.« less

  6. Spin Seebeck effect in an (In,Ga)As quantum well with equal Rashba and Dresselhaus spin-orbit couplings

    NASA Astrophysics Data System (ADS)

    Capps, Jeremy; Marinescu, D. C.; Manolescu, Andrei

    2016-02-01

    We demonstrate that a spin-dependent Seebeck effect can be detected in quantum wells with zinc-blend structure with equal Rashba-Dresselhaus spin-orbit couplings. This theory is based on the establishment of an itinerant antiferromagnetic state, a low total-energy configuration realized in the presence of the Coulomb interaction enabled by the k =0 degeneracy of the opposite-spin single-particle energy spectra. Transport in this state is modeled by using the solutions of a Boltzmann equation obtained within the relaxation time approximation. Numerical estimates performed for realistic GaAs samples indicate that at low temperatures, the amplitude of the spin Seebeck coefficient can be increased by scattering on magnetic impurities.

  7. Unambiguous separation of the inverse spin Hall and anomalous Nernst effects within a ferromagnetic metal using the spin Seebeck effect

    NASA Astrophysics Data System (ADS)

    Wu, Stephen M.; Hoffman, Jason; Pearson, John E.; Bhattacharya, Anand

    2014-09-01

    The longitudinal spin Seebeck effect is measured on the ferromagnetic insulator Fe3O4 with the ferromagnetic metal Co0.2Fe0.6B0.2 (CoFeB) as the spin detector. By using a non-magnetic spacer material between the two materials (Ti), it is possible to decouple the two ferromagnetic materials and directly observe pure spin flow from Fe3O4 into CoFeB. It is shown that in a single ferromagnetic metal, the inverse spin Hall effect (ISHE) and anomalous Nernst effect (ANE) can occur simultaneously with opposite polarity. Using this and the large difference in the coercive fields between the two magnets, it is possible to unambiguously separate the contributions of the spin Seebeck effect from the ANE and observe the degree to which each effect contributes to the total response. These experiments show conclusively that the ISHE and ANE in CoFeB are separate phenomena with different origins and can coexist in the same material with opposite response to a thermal gradient.

  8. Unambiguous separation of the inverse spin Hall and anomalous Nernst effects within a ferromagnetic metal using the spin Seebeck effect

    SciTech Connect

    Wu, Stephen M. Hoffman, Jason; Pearson, John E.; Bhattacharya, Anand

    2014-09-01

    The longitudinal spin Seebeck effect is measured on the ferromagnetic insulator Fe{sub 3}O{sub 4} with the ferromagnetic metal Co{sub 0.2}Fe{sub 0.6}B{sub 0.2} (CoFeB) as the spin detector. By using a non-magnetic spacer material between the two materials (Ti), it is possible to decouple the two ferromagnetic materials and directly observe pure spin flow from Fe{sub 3}O{sub 4} into CoFeB. It is shown that in a single ferromagnetic metal, the inverse spin Hall effect (ISHE) and anomalous Nernst effect (ANE) can occur simultaneously with opposite polarity. Using this and the large difference in the coercive fields between the two magnets, it is possible to unambiguously separate the contributions of the spin Seebeck effect from the ANE and observe the degree to which each effect contributes to the total response. These experiments show conclusively that the ISHE and ANE in CoFeB are separate phenomena with different origins and can coexist in the same material with opposite response to a thermal gradient.

  9. Spin Seebeck power generators

    SciTech Connect

    Cahaya, Adam B.; Tretiakov, O. A.; Bauer, Gerrit E. W.

    2014-01-27

    We derive expressions for the efficiency and figure of merit of two spin caloritronic devices based on the spin Seebeck effect (SSE), i.e., the generation of spin currents by a temperature gradient. The inverse spin Hall effect is conventionally used to detect the SSE and offers advantages for large area applications. We also propose a device that converts spin current into electric one by means of a spin-valve detector, which scales favorably to small sizes and approaches a figure of merit of 0.5 at room temperature.

  10. Temperature dependences of magnetic anisotropy and longitudinal spin Seebeck effect in Y3Fe5O12

    NASA Astrophysics Data System (ADS)

    Kalappattil, Vijaysankar; Das, Raja; Phan, Manh-Huong; Srikanth, Hariharan

    Spin caloritronics is an emerging, exciting research area in condensed matter owing to its potential use in advanced spintronics devices. Pure spin current without having charge current has been achieved though spin Seebeck effect (SSE). Over the last 7 years SSE has been observed in ferromagnetic metals, insulators, and semiconductors using longitudinal and transverse SSE measurement configurations. In this work, we have carried out an experimental study to understand the effect of magnetic anisotropy on the temperature evolution of longitudinal spin Seebeck effect (LSSE) in a single crystalline yttrium iron garnet (YIG). The effective anisotropy field (HK) and inverse spin Hall (ISH) voltage (VISH) were measured using the radio-frequency transverse susceptibility (TS) and LSSE configuration, respectively. The VISH of a 15 nm Pt strip on (6*2*1 mm) YIG slab with a temperature gradient of 3 K was measured in the temperature range of 120 to 300 K. The observed values of VISH vary from 1 microV for 120 K to 0.5 microV for 300 K, These values fall into the previously reported theoretical and experimental results. The temperature evolution of HKhas been compared with that of VISH to gain better fundamental understanding. Work is supported by ARO through Grant No. W911NF-15-1-0626.

  11. Spin-current Seebeck effect in an interacting quantum dot: Atomic approximation for the Anderson impurity model

    NASA Astrophysics Data System (ADS)

    Ramos, E.; Silva-Valencia, J.; Franco, R.; Siqueira, E. C.; Figueira, M. S.

    2015-11-01

    We study the spin-current Seebeck effect through an immersed gate defined quantum dot, employing the U-finite atomic method for the single impurity Anderson model. Our description qualitatively confirms some of the results obtained by an earlier Hartree-Fock work, but as our calculation includes the Kondo effect, some new features will appear in the spin-current Seebeck effect S, which as a function of the gate voltage present an oscillatory shape. At intermediate temperatures, our results show a three zero structure and at low temperatures, our results are governed by the emergence of the Kondo peak in the transmittance, which defines the behavior of the shape of the S coefficient as a function of the parameters of the model. The oscillatory behavior obtained by the Hartree-Fock approximation reproduces the shape obtained by us in a non-interacting system (U=0). The S sign is sensitive to different polarization of the quantum dot, and as a consequence the device could be employed to experimentally detect the polarization states of the system. Our results also confirm that the large increase of S upon increasing U, obtained by the mean field approximation, is correct only for low temperatures. We also discuss the role of the Kondo peak in defining the behavior of the spin thermopower at low temperatures.

  12. Thermoelectric Signal Enhancement by Reconciling the Spin Seebeck and Anomalous Nernst Effects in Ferromagnet/Non-magnet Multilayers

    PubMed Central

    Lee, Kyeong-Dong; Kim, Dong-Jun; Yeon Lee, Hae; Kim, Seung-Hyun; Lee, Jong-Hyun; Lee, Kyung-Min; Jeong, Jong-Ryul; Lee, Ki-Suk; Song, Hyon-Seok; Sohn, Jeong-Woo; Shin, Sung-Chul; Park, Byong-Guk

    2015-01-01

    The utilization of ferromagnetic (FM) materials in thermoelectric devices allows one to have a simpler structure and/or independent control of electric and thermal conductivities, which may further remove obstacles for this technology to be realized. The thermoelectricity in FM/non-magnet (NM) heterostructures using an optical heating source is studied as a function of NM materials and a number of multilayers. It is observed that the overall thermoelectric signal in those structures which is contributed by spin Seebeck effect and anomalous Nernst effect (ANE) is enhanced by a proper selection of NM materials with a spin Hall angle that matches to the sign of the ANE. Moreover, by an increase of the number of multilayer, the thermoelectric voltage is enlarged further and the device resistance is reduced, simultaneously. The experimental observation of the improvement of thermoelectric properties may pave the way for the realization of magnetic-(or spin-) based thermoelectric devices. PMID:26020492

  13. Thermoelectric Signal Enhancement by Reconciling the Spin Seebeck and Anomalous Nernst Effects in Ferromagnet/Non-magnet Multilayers.

    PubMed

    Lee, Kyeong-Dong; Kim, Dong-Jun; Yeon Lee, Hae; Kim, Seung-Hyun; Lee, Jong-Hyun; Lee, Kyung-Min; Jeong, Jong-Ryul; Lee, Ki-Suk; Song, Hyon-Seok; Sohn, Jeong-Woo; Shin, Sung-Chul; Park, Byong-Guk

    2015-01-01

    The utilization of ferromagnetic (FM) materials in thermoelectric devices allows one to have a simpler structure and/or independent control of electric and thermal conductivities, which may further remove obstacles for this technology to be realized. The thermoelectricity in FM/non-magnet (NM) heterostructures using an optical heating source is studied as a function of NM materials and a number of multilayers. It is observed that the overall thermoelectric signal in those structures which is contributed by spin Seebeck effect and anomalous Nernst effect (ANE) is enhanced by a proper selection of NM materials with a spin Hall angle that matches to the sign of the ANE. Moreover, by an increase of the number of multilayer, the thermoelectric voltage is enlarged further and the device resistance is reduced, simultaneously. The experimental observation of the improvement of thermoelectric properties may pave the way for the realization of magnetic-(or spin-) based thermoelectric devices. PMID:26020492

  14. Measuring Seebeck Coefficient

    NASA Technical Reports Server (NTRS)

    Snyder, G. Jeffrey (Inventor)

    2015-01-01

    A high temperature Seebeck coefficient measurement apparatus and method with various features to minimize typical sources of errors is described. Common sources of temperature and voltage measurement errors which may impact accurate measurement are identified and reduced. Applying the identified principles, a high temperature Seebeck measurement apparatus and method employing a uniaxial, four-point geometry is described to operate from room temperature up to 1300K. These techniques for non-destructive Seebeck coefficient measurements are simple to operate, and are suitable for bulk samples with a broad range of physical types and shapes.

  15. Thermal properties of magnons and the spin Seebeck effect in yttrium iron garnet/normal metal hybrid structures

    NASA Astrophysics Data System (ADS)

    Rezende, S. M.; Rodríguez-Suárez, R. L.; Lopez Ortiz, J. C.; Azevedo, A.

    2014-04-01

    In the study of the spin Seebeck effect (SSE) in structures with a ferromagnetic insulator (FMI) in contact with a normal metal it is important to know the distributions of the temperatures of the magnon, phonon, and electron systems. Studies of the SSE in yttrium iron garnet (YIG) have relied on the thermal properties of magnons in YIG calculated with expressions valid for low temperatures. Here we present a calculation of the magnon specific heat and thermal conductivity in YIG and show that the values at room temperature are very discrepant from numbers used in the literature. With our values we calculate the temperature profiles of the magnon and phonon systems in a FMI subject to a temperature gradient in the configurations used to study the transverse and longitudinal SSE. In both cases the results are quite different from those obtained in previous studies.

  16. High temperature Seebeck coefficient metrology

    SciTech Connect

    Martin, J.; Tritt, T.; Uher, C.

    2010-12-15

    We present an overview of the challenges and practices of thermoelectric metrology on bulk materials at high temperature (300 to 1300 K). The Seebeck coefficient, when combined with thermal and electrical conductivity, is an essential property measurement for evaluating the potential performance of novel thermoelectric materials. However, there is some question as to which measurement technique(s) provides the most accurate determination of the Seebeck coefficient at high temperature. This has led to the implementation of nonideal practices that have further complicated the confirmation of reported high ZT materials. To ensure meaningful interlaboratory comparison of data, thermoelectric measurements must be reliable, accurate, and consistent. This article will summarize and compare the relevant measurement techniques and apparatus designs required to effectively manage uncertainty, while also providing a reference resource of previous advances in high temperature thermoelectric metrology.

  17. Colossal Seebeck effect enhanced by quasi-ballistic phonons dragging massive electrons in FeSb2.

    PubMed

    Takahashi, H; Okazaki, R; Ishiwata, S; Taniguchi, H; Okutani, A; Hagiwara, M; Terasaki, I

    2016-01-01

    Phonon transport is an essential property of thermoelectric materials. Although the phonon carries heat, which reduces the thermoelectric efficiency, it contributes positively to the Seebeck coefficient S through the phonon-drag effect, as typified by the high-purity semiconductors, which show fairly large S at cryogenic temperatures. Although such a large S is attractive in terms of Peltier cooling, a clear guiding principle for designing thermoelectric materials enriched by the phonon-drag effect remains to be established. Here we demonstrate that a correlated semiconductor, FeSb2, is a promising thermoelectric material featuring quasi-ballistic phonons dragging d electrons with large effective mass. By changing the sample size within the sub-millimetre order for high-purity single crystals, we succeed in substantially increasing S to as much as -27 mV K(-1) at low temperatures. Our results exemplify a strategy for exploring phonon-drag-based thermoelectric materials, the performance of which can be maximized by combining heavy electrons with ballistic phonons. PMID:27597055

  18. Enhancement of spin-Seebeck effect by inserting ultra-thin Fe{sub 70}Cu{sub 30} interlayer

    SciTech Connect

    Kikuchi, D.; Ishida, M.; Murakami, T.; Uchida, K.; Qiu, Z.; Saitoh, E.

    2015-02-23

    We report the longitudinal spin-Seebeck effects (LSSEs) for Pt/Fe{sub 70}Cu{sub 30}/BiY{sub 2}Fe{sub 5}O{sub 12} (BiYIG) and Pt/BiYIG devices. The LSSE voltage was found to be enhanced by inserting an ultra-thin Fe{sub 70}Cu{sub 30} interlayer. This enhancement decays sharply with increasing the Fe{sub 70}Cu{sub 30} thickness, suggesting that it is not due to bulk phenomena, such as a superposition of conventional thermoelectric effects, but due to interface effects related to the Fe{sub 70}Cu{sub 30} interlayer. Combined with control experiments using Pt/Fe{sub 70}Cu{sub 30} devices, we conclude that the enhancement of the LSSE voltage in the Pt/Fe{sub 70}Cu{sub 30}/BiYIG devices is attributed to the improvement of the spin-mixing conductance at the Pt/BiYIG interfaces.

  19. Spin current injection by spin Seebeck and spin pumping effects in yttrium iron garnet/Pt structures

    NASA Astrophysics Data System (ADS)

    da Silva, G. L.; Vilela-Leão, L. H.; Rezende, S. M.; Azevedo, A.

    2012-04-01

    It is reported an investigation of pure spin current injection in Pt strips deposited on yttrium iron garnet (YIG) films by means of the spin pumping (SPE) and spin Seebeck (SSE) effects. Both effects were characterized by measuring the DC voltage created along the Pt strips by means of the inverse spin Hall effect (VISHE). SPE and SSE are simultaneously activated by exciting the ferromagnetic resonance (FMR) of the YIG film at the same time that a temperature gradient is created along the sample length. While the FMR signal is little affected by the temperature gradient, the voltage measured at the Pt strip placed at the lower temperature end exhibits a very challenging behavior. The voltage excited by the FMR uniform mode increases by six times as the temperature difference (ΔT) between the two ends of the YIG slab changes from 0 to 12 K. In contrast the VISHE generated by other magnetostatic spin-wave modes decreases to zero as ΔT varies from 0 to 12 K.

  20. Spin-dependent Seebeck Effect, Thermal Colossal Magnetoresistance and Negative Differential Thermoelectric Resistance in Zigzag Silicene Nanoribbon Heterojunciton

    PubMed Central

    Fu, Hua-Hua; Wu, Dan-Dan; Zhang, Zu-Quan; Gu, Lei

    2015-01-01

    Spin-dependent Seebeck effect (SDSE) is one of hot topics in spin caloritronics, which examine the relationships between spin and heat transport in materials. Meanwhile, it is still a huge challenge to obtain thermally induced spin current nearly without thermal electron current. Here, we construct a hydrogen-terminated zigzag silicene nanoribbon heterojunction, and find that by applying a temperature difference between the source and the drain, spin-up and spin-down currents are generated and flow in opposite directions with nearly equal magnitudes, indicating that the thermal spin current dominates the carrier transport while the thermal electron current is much suppressed. By modulating the temperature, a pure thermal spin current can be achieved. Moreover, a thermoelectric rectifier and a negative differential thermoelectric resistance can be obtained in the thermal electron current. Through the analysis of the spin-dependent transport characteristics, a phase diagram containing various spin caloritronic phenomena is provided. In addition, a thermal magnetoresistance, which can reach infinity, is also obtained. Our results put forward an effective route to obtain a spin caloritronic material which can be applied in future low-power-consumption technology. PMID:26000658

  1. Charge carrier effective mass and concentration derived from combination of Seebeck coefficient and 125Te NMR measurements in complex tellurides

    NASA Astrophysics Data System (ADS)

    Levin, E. M.

    2016-06-01

    Thermoelectric materials utilize the Seebeck effect to convert heat to electrical energy. The Seebeck coefficient (thermopower), S , depends on the free (mobile) carrier concentration, n , and effective mass, m*, as S ˜m*/n2 /3 . The carrier concentration in tellurides can be derived from 125Te nuclear magnetic resonance (NMR) spin-lattice relaxation measurements. The NMR spin-lattice relaxation rate, 1 /T1 , depends on both n and m* as 1 /T1˜(m*)3/2n (within classical Maxwell-Boltzmann statistics) or as 1 /T1˜(m*)2n2 /3 (within quantum Fermi-Dirac statistics), which challenges the correct determination of the carrier concentration in some materials by NMR. Here it is shown that the combination of the Seebeck coefficient and 125Te NMR spin-lattice relaxation measurements in complex tellurides provides a unique opportunity to derive the carrier effective mass and then to calculate the carrier concentration. This approach was used to study A gxS bxG e50-2xT e50 , well-known GeTe-based high-efficiency tellurium-antimony-germanium-silver thermoelectric materials, where the replacement of Ge by [Ag+Sb] results in significant enhancement of the Seebeck coefficient. Values of both m* and n derived using this combination show that the enhancement of thermopower can be attributed primarily to an increase of the carrier effective mass and partially to a decrease of the carrier concentration when the [Ag+Sb] content increases.

  2. Effects of Ge replacement in GeTe by Ag or Sb on the Seebeck coefficient and carrier concentration modified by local electron imbalance

    NASA Astrophysics Data System (ADS)

    Levin, E. M.; Howard, A.; Straszheim, W. E.

    2015-03-01

    XRD, SEM, EDS, 125Te NMR, Seebeck coefficient, and electrical resistivity of AgxGe50-xTe50 and SbxGe50-xTe50 alloys have been studied. Replacement of Ge in GeTe by Sb significantly increases the Seebeck coefficient, while replacement by Ag decreases it. These effects can be attributed to a change in carrier concentration observed via 125Te NMR spin-lattice relaxation measurements and NMR signal position, which mostly depends on the Knight shift. Variation in carrier concentration in AgxGe50-xTe50 and SbxGe50-xTe50 can be attributed to different electron configurations of valence electrons of Ag (4d105s1) and Sb (5s25p3) compared to that of Ge (4s24p2) resulting in local electron imbalances and changing the concentration of charge carrier (holes) generated by Ge vacancies. In contrast, our 125Te NMR and Seebeck coefficient data for Ag2Sb2Ge46Te50 are similar to those observed for GeTe. This shows that effects from Ag and Sb compensate each other and indicates the existence of [Ag +Sb] pairs. The effects of Ge replacement in GeTe by Ag, Sb, or [Ag +Sb] on rhombohedral lattice distortion also have been analyzed. Interplay between the Seebeck coefficient and electrical resistivity in these alloys results in variation of power factor; the value of 45 mW/cm K2, the highest among known tellurides, was found for Sb2Ge48Te50.

  3. Separation of the inverse spin Hall effect and anomalous Nernst effect in a single ferromagnetic metal using on-chip spin Seebeck devices

    NASA Astrophysics Data System (ADS)

    Wu, Stephen; Hoffman, Jason; Pearson, John; Bhattacharya, Anand

    The longitudinal spin Seebeck effect is measured on the ferromagnetic insulator Fe3O4 with the ferromagnetic metal Co0.2Fe0.6B0.2 (CoFeB) as the spin detector in a micro-patterned device structure using an on-chip heater. By using a non-magnetic spacer material between the two materials (Ti), it is possible to decouple the two ferromagnetic materials and directly observe pure spin flow from Fe3O4 into CoFeB. It is shown, that in a single ferromagnetic metal the inverse spin Hall effect (ISHE) and anomalous Nernst effect (ANE) can occur simultaneously with opposite polarity. Using this and the large difference in the coercive fields between the two magnets, it is possible to unambiguously separate the contributions of the spin Seebeck effect from the ANE and observe the degree to which each effect contributes to the total response within a single experiment. Additionally, by using the spin detector layer as a thermometer, an accurate value for the thermal gradient across the device can be measured. These results match well with thermal simulations of our device structure. All authors acknowledge support of the U.S. Department of Energy (DOE), Office of Science, Basic Energy Sciences (BES), Materials Sciences and Engineering Division.

  4. Huge Seebeck coefficients in nonaqueous electrolytes

    NASA Astrophysics Data System (ADS)

    Bonetti, M.; Nakamae, S.; Roger, M.; Guenoun, P.

    2011-03-01

    The Seebeck coefficients of the nonaqueous electrolytes tetrabutylammonium nitrate, tetraoctylphosphonium bromide, and tetradodecylammonium nitrate in 1-octanol, 1-dodecanol, and ethylene-glycol are measured in a temperature range from T = 30 °C to T = 45 °C. The Seebeck coefficient is generally of the order of a few hundreds of microvolts per Kelvin for aqueous solution of inorganic ions. Here we report huge values of 7 mV/K at 0.1 M concentration for tetrabutylammonium nitrate in 1-dodecanol. These striking results open the question of unexpectedly large kosmotrope or "structure making" effects of tetraalkylammonium ions on the structure of alcohols.

  5. Joule heating-induced coexisted spin Seebeck effect and spin Hall magnetoresistance in the platinum/Y{sub 3}Fe{sub 5}O{sub 12} structure

    SciTech Connect

    Wang, W. X.; Wang, S. H.; Zou, L. K.; Cai, J. W.; Sun, J. R. E-mail: sun-zg@whut.edu.cn; Sun, Z. G.

    2014-11-03

    Spin Seebeck effect (SSE) and spin Hall magnetoresistance (SMR) are observed simultaneously in the Pt/Y{sub 3}Fe{sub 5}O{sub 12} hybrid structure when thermal gradient is produced by Joule heating. According to their dependences on applied current, these two effects can be separated. Their dependence on heating power and magnetic field is systematically studied. With the increase of heating power, the SSE enhances linearly, whereas the SMR decreases slowly. The origin of the spin currents is further analyzed. The heating power dependences of the spin currents associated with the SSE and the SMR are found to be different.

  6. Seebeck Effects in N-Type and P-Type Polymers Driven Simultaneously by Surface Polarization and Entropy Differences Based on Conductor/Polymer/Conductor Thin-Film Devices

    SciTech Connect

    Hu, Dehua; Liu, Qing; Tisdale, Jeremy; Lei, Ting; Pei, Jian; Wang, Hsin; Urbas, Augustine; Hu, Bin

    2015-04-15

    This paper reports Seebeck effects driven by both surface polarization difference and entropy difference by using intramolecular charge-transfer states in n-type and p-type conjugated polymers, namely IIDT and IIDDT, based on vertical conductor/polymer/conductor thin-film devices. Large Seebeck coefficients of -898 V/K and 1300 V/K from are observed from n-type IIDT p-type IIDDT, respectively, when the charge-transfer states are generated by a white light illumination of 100 mW/cm2. Simultaneously, electrical conductivities are increased from almost insulating states in dark condition to conducting states under photoexcitation in both n-type IIDT and p-type IIDDT devices. We find that the intramolecular charge-transfer states can largely enhance Seebeck effects in the n-type IIDT and p-type IIDDT devices driven by both surface polarization difference and entropy difference. Furthermore, the Seebeck effects can be shifted between polarization and entropy regimes when electrical conductivities are changed. This reveals a new concept to develop Seebeck effects by controlling polarization and entropy regimes based on charge-transfer states in vertical conductor/polymer/conductor thin-film devices.

  7. Seebeck Effects in N-Type and P-Type Polymers Driven Simultaneously by Surface Polarization and Entropy Differences Based on Conductor/Polymer/Conductor Thin-Film Devices

    DOE PAGESBeta

    Hu, Dehua; Liu, Qing; Tisdale, Jeremy; Lei, Ting; Pei, Jian; Wang, Hsin; Urbas, Augustine; Hu, Bin

    2015-04-15

    This paper reports Seebeck effects driven by both surface polarization difference and entropy difference by using intramolecular charge-transfer states in n-type and p-type conjugated polymers, namely IIDT and IIDDT, based on vertical conductor/polymer/conductor thin-film devices. Large Seebeck coefficients of -898 V/K and 1300 V/K from are observed from n-type IIDT p-type IIDDT, respectively, when the charge-transfer states are generated by a white light illumination of 100 mW/cm2. Simultaneously, electrical conductivities are increased from almost insulating states in dark condition to conducting states under photoexcitation in both n-type IIDT and p-type IIDDT devices. We find that the intramolecular charge-transfer states canmore » largely enhance Seebeck effects in the n-type IIDT and p-type IIDDT devices driven by both surface polarization difference and entropy difference. Furthermore, the Seebeck effects can be shifted between polarization and entropy regimes when electrical conductivities are changed. This reveals a new concept to develop Seebeck effects by controlling polarization and entropy regimes based on charge-transfer states in vertical conductor/polymer/conductor thin-film devices.« less

  8. Flexible heat-flow sensing sheets based on the longitudinal spin Seebeck effect using one-dimensional spin-current conducting films

    PubMed Central

    Kirihara, Akihiro; Kondo, Koichi; Ishida, Masahiko; Ihara, Kazuki; Iwasaki, Yuma; Someya, Hiroko; Matsuba, Asuka; Uchida, Ken-ichi; Saitoh, Eiji; Yamamoto, Naoharu; Kohmoto, Shigeru; Murakami, Tomoo

    2016-01-01

    Heat-flow sensing is expected to be an important technological component of smart thermal management in the future. Conventionally, the thermoelectric (TE) conversion technique, which is based on the Seebeck effect, has been used to measure a heat flow by converting the flow into electric voltage. However, for ubiquitous heat-flow visualization, thin and flexible sensors with extremely low thermal resistance are highly desired. Recently, another type of TE effect, the longitudinal spin Seebeck effect (LSSE), has aroused great interest because the LSSE potentially offers favourable features for TE applications such as simple thin-film device structures. Here we demonstrate an LSSE-based flexible TE sheet that is especially suitable for a heat-flow sensing application. This TE sheet contained a Ni0.2Zn0.3Fe2.5O4 film which was formed on a flexible plastic sheet using a spray-coating method known as “ferrite plating”. The experimental results suggest that the ferrite-plated film, which has a columnar crystal structure aligned perpendicular to the film plane, functions as a unique one-dimensional spin-current conductor suitable for bendable LSSE-based sensors. This newly developed thin TE sheet may be attached to differently shaped heat sources without obstructing an innate heat flux, paving the way to versatile heat-flow measurements and management. PMID:26975208

  9. Flexible heat-flow sensing sheets based on the longitudinal spin Seebeck effect using one-dimensional spin-current conducting films

    NASA Astrophysics Data System (ADS)

    Kirihara, Akihiro; Kondo, Koichi; Ishida, Masahiko; Ihara, Kazuki; Iwasaki, Yuma; Someya, Hiroko; Matsuba, Asuka; Uchida, Ken-Ichi; Saitoh, Eiji; Yamamoto, Naoharu; Kohmoto, Shigeru; Murakami, Tomoo

    2016-03-01

    Heat-flow sensing is expected to be an important technological component of smart thermal management in the future. Conventionally, the thermoelectric (TE) conversion technique, which is based on the Seebeck effect, has been used to measure a heat flow by converting the flow into electric voltage. However, for ubiquitous heat-flow visualization, thin and flexible sensors with extremely low thermal resistance are highly desired. Recently, another type of TE effect, the longitudinal spin Seebeck effect (LSSE), has aroused great interest because the LSSE potentially offers favourable features for TE applications such as simple thin-film device structures. Here we demonstrate an LSSE-based flexible TE sheet that is especially suitable for a heat-flow sensing application. This TE sheet contained a Ni0.2Zn0.3Fe2.5O4 film which was formed on a flexible plastic sheet using a spray-coating method known as “ferrite plating”. The experimental results suggest that the ferrite-plated film, which has a columnar crystal structure aligned perpendicular to the film plane, functions as a unique one-dimensional spin-current conductor suitable for bendable LSSE-based sensors. This newly developed thin TE sheet may be attached to differently shaped heat sources without obstructing an innate heat flux, paving the way to versatile heat-flow measurements and management.

  10. Flexible heat-flow sensing sheets based on the longitudinal spin Seebeck effect using one-dimensional spin-current conducting films.

    PubMed

    Kirihara, Akihiro; Kondo, Koichi; Ishida, Masahiko; Ihara, Kazuki; Iwasaki, Yuma; Someya, Hiroko; Matsuba, Asuka; Uchida, Ken-ichi; Saitoh, Eiji; Yamamoto, Naoharu; Kohmoto, Shigeru; Murakami, Tomoo

    2016-01-01

    Heat-flow sensing is expected to be an important technological component of smart thermal management in the future. Conventionally, the thermoelectric (TE) conversion technique, which is based on the Seebeck effect, has been used to measure a heat flow by converting the flow into electric voltage. However, for ubiquitous heat-flow visualization, thin and flexible sensors with extremely low thermal resistance are highly desired. Recently, another type of TE effect, the longitudinal spin Seebeck effect (LSSE), has aroused great interest because the LSSE potentially offers favourable features for TE applications such as simple thin-film device structures. Here we demonstrate an LSSE-based flexible TE sheet that is especially suitable for a heat-flow sensing application. This TE sheet contained a Ni0.2Zn0.3Fe2.5O4 film which was formed on a flexible plastic sheet using a spray-coating method known as "ferrite plating". The experimental results suggest that the ferrite-plated film, which has a columnar crystal structure aligned perpendicular to the film plane, functions as a unique one-dimensional spin-current conductor suitable for bendable LSSE-based sensors. This newly developed thin TE sheet may be attached to differently shaped heat sources without obstructing an innate heat flux, paving the way to versatile heat-flow measurements and management. PMID:26975208

  11. Detection of DC currents and resistance measurements in longitudinal spin Seebeck effect experiments on Pt/YIG and Pt/NFO

    NASA Astrophysics Data System (ADS)

    Meier, Daniel; Kuschel, Timo; Meyer, Sibylle; Goennenwein, Sebastian T. B.; Shen, Liming; Gupta, Arunava; Schmalhorst, Jan-Michael; Reiss, Günter

    2016-05-01

    In this work we investigated thin films of the ferrimagnetic insulators Y 3Fe5O12 and NiFe2O4 capped with thin Pt layers in terms of the longitudinal spin Seebeck effect (LSSE). The electric response detected in the Pt layer under an out-of-plane temperature gradient can be interpreted as a pure spin current converted into a charge current via the inverse spin Hall effect. Typically, the transverse voltage is the quantity investigated in LSSE measurements (in the range of μV). Here, we present the directly detected DC current (in the range of nA) as an alternative quantity. Furthermore, we investigate the resistance of the Pt layer in the LSSE configuration. We found an influence of the test current on the resistance. The typical shape of the LSSE curve varies for increasing test currents.

  12. Intrinsic surface magnetic anisotropy in Y3Fe5O12 as the origin of low-magnetic-field behavior of the spin Seebeck effect

    NASA Astrophysics Data System (ADS)

    Uchida, Ken-ichi; Ohe, Jun-ichiro; Kikkawa, Takashi; Daimon, Shunsuke; Hou, Dazhi; Qiu, Zhiyong; Saitoh, Eiji

    2015-07-01

    The magnetic-field dependence of the longitudinal spin Seebeck effect (LSSE) in a Pt /Y3Fe5O12 (YIG)-slab junction system was found to deviate from a bulk magnetization curve of the YIG slab in a low field range. In this paper, we show that the deviation originates from the difference between surface and bulk magnetization processes in the YIG slab and that it appears even when removing possible extrinsic magnetic anisotropy due to surface roughness and replacing the Pt layer with different materials. This result indicates that the anomalous field dependence of the LSSE is due to an intrinsic magnetic property of the YIG surface. Our numerical calculation based on the Landau-Lifshitz-Gilbert equation shows that the deviation between the LSSE and bulk magnetization curves is qualitatively explained by introducing easy-axis perpendicular magnetic anisotropy near the surface of YIG.

  13. Seebeck effects in n-type and p-type polymers driven simultaneously by surface polarization and entropy differences based on conductor/polymer/conductor thin-film devices.

    PubMed

    Hu, Dehua; Liu, Qing; Tisdale, Jeremy; Lei, Ting; Pei, Jian; Wang, Hsin; Urbas, Augustine; Hu, Bin

    2015-05-26

    This paper reports Seebeck effects driven by both surface polarization difference and entropy difference by using photoinduced intramolecular charge-transfer states in n-type and p-type conjugated polymers, namely IIDT and IIDDT, respectively, based on vertical conductor/polymer/conductor thin-film devices. We obtain large Seebeck coefficients of -898 μV/K from n-type IIDT and 1300 μV/K from p-type IIDDT when the charge-transfer states are generated by a white light illumination of 100 mW/cm(2), compared with the values of 380 and 470 μV/K in dark condition, respectively. Simultaneously, the electrical conductivities are increased from almost insulating state in dark condition to conducting state under photoexcitation in both n-type IIDT and p-type IIDDT based devices. The large Seebeck effects can be attributed to the following two mechanisms. First, the intramolecular charge-transfer states exhibit strong electron-phonon coupling, which leads to a polarization difference between high and low temperature surfaces. This polarization difference essentially forms a temperature-dependent electric field, functioning as a new driving force additional to entropy difference, to drive the energetic carriers for the development of Seebeck effects under a temperature difference. Second, the intramolecular charge-transfer states generate negative or positive majority carriers (electrons or holes) in the n-type IIDT or p-type IIDDT, ready to be driven between high and low temperature surfaces for developing Seebeck effects. On the basis of coexisted polarization difference and entropy difference, the intramolecular charge-transfer states can largely enhance the Seebeck effects in both n-type IIDT and p-type IIDDT devices. Furthermore, we find that changing electrical conductivity can switch the Seebeck effects between polarization and entropy regimes when the charge-transfer states are generated upon applying photoexcitation. Therefore, using intramolecular charge

  14. Apparatus for measuring the Seebeck coefficients of highly resistive organic semiconducting materials

    NASA Astrophysics Data System (ADS)

    Cai, H. Y.; Cui, D. F.; Li, Y. T.; Chen, X.; Zhang, L. L.; Sun, J. H.

    2013-04-01

    A Seebeck coefficient measurement apparatus for high resistance organic semiconductor materials has been designed and built. It can measure materials with resistance over 7 × 1012 Ω. This is the highest material resistance value ever reported for Seebeck coefficient measurement. A cyclic temperature gradient generation technique and a corresponding algorithm are proposed to eliminate the negative effects of the long term drift of Seebeck voltage. Sources of errors in these measurements are discussed.

  15. Ultrafast demagnetization, spin-dependent Seebeck effect, and thermal spin transfer torque in Pt/TbFe/Cu and Pt/TbFe/Cu/Fe thin films

    NASA Astrophysics Data System (ADS)

    Kimling, Johannes; Hebler, Birgit; Kimling, Judith; Albrecht, Manfred; Cahill, David G.

    We investigate diffusive spin currents in Pt(20nm)/TbFe(10nm)/Cu(100nm) and Pt(20 nm)/TbFe(10nm)/ Cu(100nm)/Fe(3nm) stacks using time-resolved magneto-optic Kerr effect (TRMOKE) and time-domain thermoreflectance measurements. Our experiments are based on two hypothesis: (1) fast changes of magnetization due to laser excitation are transferred into spin accumulation, e.g., via electron-magnon scattering; the generated spin accumulation drives a diffusive spin current into adjacent normal metal layers; (2) electronic thermal transport through the ferromagnetic layer injects a spin current into adjacent normal metal layers, based on the spin-dependent Seebeck effect. We excite the Pt layer with ps-laser pulses. Resulting diffusive spin currents generate nonequilibrium magnetization in the Cu layer (sample I) and induce a precession of the magnetization of the Fe layer via spin transfer torque (sample II). Both responses are probed using TRMOKE. Prior experiments used [Co(0.2nm)/Pt(0.4nm)]x5/Co(0.2nm) instead of TbFe. The ferrimagnetic TbFe layer with introduces two major modifications: (1) slow demagnetization behavior, and (2) large thermal resistance. Hence, thermal spin transfer torques can be observed on significantly longer time scales. Financial support by the German Research Foundation under DFG-Grant No. KI 1893/1-1 and DFG-Grant No. AL 618/21-1 are kindly acknowledged.

  16. Uncertainty analysis for common Seebeck and electrical resistivity measurement systems.

    PubMed

    Mackey, Jon; Dynys, Frederick; Sehirlioglu, Alp

    2014-08-01

    This work establishes the level of uncertainty for electrical measurements commonly made on thermoelectric samples. The analysis targets measurement systems based on the four probe method. Sources of uncertainty for both electrical resistivity and Seebeck coefficient were identified and evaluated. Included are reasonable estimates on the magnitude of each source, and cumulative propagation of error. Uncertainty for the Seebeck coefficient includes the cold-finger effect which has been quantified with thermal finite element analysis. The cold-finger effect, which is a result of parasitic heat transfer down the thermocouple probes, leads to an asymmetric over-estimation of the Seebeck coefficient. A silicon germanium thermoelectric sample has been characterized to provide an understanding of the total measurement uncertainty. The electrical resistivity was determined to contain uncertainty of ±7.0% across any measurement temperature. The Seebeck coefficient of the system is +1.0%/-13.1% at high temperature and ±1.0% near room temperature. The power factor has a combined uncertainty of +7.3%/-27.0% at high temperature and ±7.5% near room temperature. These ranges are calculated to be typical values for a general four probe Seebeck and resistivity measurement configuration. PMID:25173324

  17. Spin Seebeck devices using local on-chip heating

    SciTech Connect

    Wu, Stephen M. Fradin, Frank Y.; Hoffman, Jason; Hoffmann, Axel; Bhattacharya, Anand

    2015-05-07

    A micro-patterned spin Seebeck device is fabricated using an on-chip heater. Current is driven through a Au heater layer electrically isolated from a bilayer consisting of Fe{sub 3}O{sub 4} (insulating ferrimagnet) and a spin detector layer. It is shown that through this method it is possible to measure the longitudinal spin Seebeck effect (SSE) for small area magnetic devices, equivalent to traditional macroscopic SSE experiments. Using a lock-in detection technique, it is possible to more sensitively characterize both the SSE and the anomalous Nernst effect (ANE), as well as the inverse spin Hall effect in various spin detector materials. By using the spin detector layer as a thermometer, we can obtain a value for the temperature gradient across the device. These results are well matched to values obtained through electromagnetic/thermal modeling of the device structure and with large area spin Seebeck measurements.

  18. Effects of Ge substitution in GeTe by Ag or Sb on the Seebeck coefficient and carrier concentration derived from 125Te NMR

    NASA Astrophysics Data System (ADS)

    Levin, E. M.

    2016-01-01

    GeTe, a self-doping p -type semiconductor where the high free hole concentration is determined by Ge vacancies is a well-known base for high-efficiency A gxS bxG e50 -2 xT e50 (a tellurium-antimony-germanium-silver series) thermoelectric materials. Here it is shown that the replacement of Ge by Ag in GeTe (a A gxG e50 -xT e50 system) significantly decreases the Seebeck coefficient, whereas the replacement by Sb (S bxG e50 -xT e50 ) increases it. These effects can be attributed to a change in carrier concentration and consistent with 125Te NMR spin-lattice relaxation measurements and NMR signal position, which is mostly dependent on the Knight shift. Opposite changes in carrier concentration in A gxG e50 -xT e50 and S bxG e50 -xT e50 can be explained by different valence electron configurations of Ag and Sb compared to that of Ge, which results in a different local electron imbalance and/or in a change in Ge vacancy formation energy and affects the total carrier concentration. Comparison of our data for GeTe, A g2G e48T e50 , and S b2G e48T e50 with those for A g2S b2G e46T e50 shows that the effects from Ag and Sb compensate for each other and supports the formation of [Ag +Sb ] atomic pairs suggested earlier based on theoretical calculations.

  19. First-principles simulation on Seebeck coefficient in silicon and silicon carbide nanosheets

    NASA Astrophysics Data System (ADS)

    Nakamura, Koichi

    2016-06-01

    The Seebeck coefficients of silicon and silicon carbide for both bulk and nanosheet structures were simulated on the basis of first-principles calculation. The simulation procedure by means of the electronic band structure with periodic boundary condition is presented, and the dependences of the Seebeck coefficient on temperature and carrier concentration have been demonstrated for many kinds of n- or p-doped models. Under the assumption that the relaxation time is constant regardless of energy, the calculated Seebeck coefficients for bulk structures are mostly in accordance with the measured values quantitatively. The typical quantum-mechanical confinement can be observed for all nanosheet models in this study owing to dimensional reduction from bulk to nanosheet structure, but it is not so effective on the Seebeck coefficient. By the simulation with consideration of the energy dependence of the relaxation time, it is confirmed that the Seebeck coefficient should be significantly affected by the relaxation time in a wide range of temperature.

  20. The Seebeck coefficient of superionic conductors

    SciTech Connect

    Mahan, G. D.

    2015-01-28

    We present a theory of the anomalous Seebeck coefficient found in the superionic conductor Cu{sub 2}Se. It has a phase transition at T = 400 K where the cations disorder but the anions do not. This disorder gives a temperature-dependent width to the electronic states in the conduction band. This width provides the anomalous Seebeck contribution.

  1. Comparison of laser-induced and intrinsic tunnel magneto-Seebeck effect in CoFeB /MgAl2O4 and CoFeB/MgO magnetic tunnel junctions

    NASA Astrophysics Data System (ADS)

    Huebner, Torsten; Boehnke, Alexander; Martens, Ulrike; Thomas, Andy; Schmalhorst, Jan-Michael; Reiss, Günter; Münzenberg, Markus; Kuschel, Timo

    2016-06-01

    We present a comparison of the tunnel magneto-Seebeck effect for laser-induced and intrinsic heating. Therefore, Co40Fe40B20 /MgAl2O4 and Co25Fe55B20 /MgO magnetic tunnel junctions have been prepared. The TMS ratio of 3% in case of the MAO MTJ agrees well with ratios found for other barrier materials, while the TMS ratio of 23% of the MgO MTJ emphasizes the influence of the CoFe composition. We find results using the intrinsic method that differ in sign and magnitude in comparison to the results of the laser heating. The intrinsic contributions can alternatively be explained by the Brinkman model and the given junction properties. Especially, we are able to demonstrate that the symmetric contribution is solely influenced by the barrier asymmetry. Thus, we conclude that the symmetry analysis used for the intrinsic method is not suitable to unambiguously identify an intrinsic tunnel magneto-Seebeck effect.

  2. Conductivities and Seebeck coefficients of boron carbides: Softening bipolaron hopping

    NASA Astrophysics Data System (ADS)

    Aselage, T. L.; Emin, D.; McCready, S. S.

    2001-08-01

    The electrical conductivities and Seebeck coefficients of boron carbides B12+xC3-x with 0.06<~x<~1.7 have been measured from 8 K to as high as 1750 K. At high temperature, the temperature dependence of the conductivities is Arrhenius and the activation energy, ~0.16 eV, is independent of the carbon concentration. The preexponential factors of the conductivity exhibit a nonmonotonic dependence on x, peaking near x=1. These results are consistent with a previously proposed model based on holes forming singlet bipolarons on the boron carbide B11C icosahedra. At low temperature, the boron carbide conductivities are non-Arrhenius with a temperature dependence that is a strong function of the composition x. This strong sensitivity to composition indicates that percolation effects, arising from boron carbides having carbon atoms in inequivalent locations, influence the conductivity at low temperature. With x holes per unit cell, boron carbides have very large Seebeck coefficients that depend only weakly on x. The magnitudes and temperature dependences of the Seebeck coefficients are consistent with large contributions from carrier-induced softening of local vibrations. Softening effects can be exceptionally large when singlet bipolarons are stabilized among degenerate electronic energy levels by their softening of symmetry-breaking vibrations: ``softening bipolarons.'' The boron carbide transport properties are generally consistent with those expected of softening bipolarons. Finally, two high-temperature effects are observed in the boron carbide conductivities. The conductivities of samples having high carrier densities, x~1, are suppressed above 700 K. This suppression can arise when the rapid hopping of nearby carriers disrupts the energy coincidence required for a carrier's hop. At even higher temperatures, a sharp increase in the boron carbide conductivities (σ~T4) suggests a radiation-induced excitation of mobile charge carriers.

  3. First-principles analysis on Seebeck coefficient in zinc oxide nanowires for thermoelectric devices

    NASA Astrophysics Data System (ADS)

    Nakamura, K.

    2016-03-01

    The Seebeck coefficient of ZnO<0001> nanowires was simulated on the basis of first- principles calculation, to discuss the potential for future application to thermoelectric devices. Simulation procedure by means of the electronic band structure with one-dimensional periodic boundary condition was presented, and dependences of the Seebeck coefficient on temperature and carrier concentration have been investigated for many kinds of n- or p-doped ZnO<0001> nanowire models with 1.00-2.65 nm diameter. For the direct band-gap semiconducting models, a magnitude of the Seebeck coefficient increases gradually as temperature rises in the p-doped state, and a significant effect of miniaturization to nanowire on the Seebeck coefficient has been brought out, such as about 1000 µV/K in the p-doped state and -820 µV/K in the n-doped state for the (ZnO)24 nanowire model with 1 × 1017 cm-3 carrier concentration at room temperature. Similar characteristics of the Seebeck coefficient were observed for some indirect band-gap semiconducting models. At the end of this paper, the simulation was extended to the no band-gap conducting models with some modification.

  4. Protocols for the high temperature measurement of the Seebeck coefficient in thermoelectric materials

    NASA Astrophysics Data System (ADS)

    Martin, Joshua

    2013-08-01

    In Seebeck coefficient metrology, the present diversity in apparatus design, acquisition methodology and contact geometry has resulted in conflicting materials data that complicate the interlaboratory confirmation of reported high efficiency thermoelectric materials. To elucidate the influence of these factors in the measurement of the Seebeck coefficient at high temperature and to identify optimal metrology protocols, we measure the Seebeck coefficient as a function of contact geometry under both steady-state and transient thermal conditions of the differential method, using a custom developed apparatus capable of in situ comparative measurement. The thermal gradient formation and data acquisition methodology, under ideal conditions, have little effect on the measured Seebeck coefficient value. However, the off-axis 4-probe contact geometry, as compared to the 2-probe, results in a greater local temperature measurement error that increases with temperature. For surface temperature measurement, the dominant thermal errors arise from a parasitic heat flux that is dependent on the temperature difference between the sample and the external thermal environment, and on the various thermal resistances. Due to higher macroconstriction and contact resistance in the 4-probe arrangement, the measurement of surface temperature for this contact geometry exhibits greater error, thereby overestimating the Seebeck coefficient.

  5. Longitudinal spin Seebeck effect in Nd{sub 2}BiFe{sub 5−x}Ga{sub x}O{sub 12} prepared on gadolinium gallium garnet (001) by metal organic decomposition method

    SciTech Connect

    Asada, H. Kuwahara, A.; Sakata, N.; Ono, T.; Kishimoto, K.; Koyanagi, T.; Ishibashi, T.; Meguro, A.; Hashinaka, T.

    2015-05-07

    Nd{sub 2}BiFe{sub 5−x}Ga{sub x}O{sub 12} thin films with the Ga composition x = 0, 0.5, and 1.0 are prepared on (001) oriented gadolinium gallium garnet substrates by a metal organic decomposition method. Only (001) peaks are observed in x-ray diffraction patterns for all the films, suggesting that the highly oriented Nd{sub 2}BiFe{sub 5−x}Ga{sub x}O{sub 12} thin films were formed. Increasing Ga composition, the saturation magnetization decreases, and the perpendicular easy axis is enhanced due to the decrease of the shape anisotropy. Longitudinal spin Seebeck effects (LSSEs) in Nd{sub 2}BiFe{sub 5−x}Ga{sub x}O{sub 12} thin films with a Pt layer of 10 nm in thickness were investigated. Magnetic field dependence of the thermoelectric voltage caused by the LSSE in Nd{sub 2}BiFe{sub 5−x}Ga{sub x}O{sub 12} films indicates the hysteresis loop with the small coercivity reflecting the magnetization curve. The decrease of LSSE voltage in Nd{sub 2}BiFe{sub 5−x}Ga{sub x}O{sub 12} is clearly observed with the decrease of Fe composition.

  6. Scanning measurement of Seebeck coefficient of a heated sample

    DOEpatents

    Snyder, G. Jeffrey; Iwanaga, Shiho

    2016-04-19

    A novel scanning Seebeck coefficient measurement technique is disclosed utilizing a cold scanning thermocouple probe tip on heated bulk and thin film samples. The system measures variations in the Seebeck coefficient within the samples. The apparatus may be used for two dimensional mapping of the Seebeck coefficient on the bulk and thin film samples. This technique can be utilized for detection of defective regions, as well as phase separations in the sub-mm range of various thermoelectric materials.

  7. Description of a Sensitive Seebeck Calorimeter Used for Cold Fusion Studies

    NASA Astrophysics Data System (ADS)

    Storms, Edmund

    A sensitive and stable Seebeck calorimeter is described and used to determine the heat of formation of PdD. This determination can be used to show that such calorimeters are sufficiently accurate to measure the LENR effect and give support to the claims.

  8. Nerst and Seebeck magneto-transport properties of LaFeAsO from first principles

    NASA Astrophysics Data System (ADS)

    Bernardini, Fabio; Caglieris, Federico; Pallecchi, Ilaria; Manfrinetti, Pietro; Provino, Alessia; Lamura, Gianrico; Putti, Marina

    2014-03-01

    Iron based superconductors such as Ba(FeAs)2 and LaFeAsO share with graphene the presence of Dirac cone (DC) states whose existence was confirmed by the linear dependence of the magneto-resistance behavior at low temperature. The formation of DCs is due to the presence of a spin density wave (SDW) ordered state below the the Neel temperature. The Nerst and Seebeck effects have recently proven to be sensitive probes for detecting unusual normal state properties of unconventional superconductors. In particular Nerst effect may sensitively detect Fermi reconstructions that are connected to a SDW ordered state. Here we focus on the LaFeAsO compound whose ground state exhibits static stripe order. The presence of a SDW leads to a large Nerst response. Experiments so far have not yielded a unified picture on the trend in temperature of the Nerst and Seebeck coefficients. To shed light on the experiments we computed the Nerst and Seebeck coefficients for LaFeAsO from first principles in the framework of density functional theory and Bloch-Boltzmann equations. Our results help to understand the trend in temperature of both Nerst and Seebeck effects. We acknowledge financial support from FP7 European project SUPER-IRON (Grant agreement No. 283204).

  9. High Seebeck Coefficient of Porous Silicon: Study of the Porosity Dependence

    NASA Astrophysics Data System (ADS)

    Valalaki, Katerina; Benech, Philippe; Galiouna Nassiopoulou, Androula

    2016-04-01

    In-plane Seebeck coefficient of porous Si free-standing membranes of different porosities was accurately measured at room temperature. Quasi-steady-state differential Seebeck coefficient method was used for the measurements. A detailed description of our home-built setup is presented. The Seebeck coefficient was proved to increase with increasing porosity up to a maximum of ~1 mV/K for the ~50 % porosity membrane, which is more than a threefold increase compared to the starting highly doped bulk c-Si substrate. By further increasing porosity and after a maximum is reached, the Seebeck coefficient sharply decreases and stabilizes at ~600 μV/K. The possible mechanisms that determine this behaviour are discussed, supported by structural characterization and photoluminescence measurements. The decrease in nanostructure size and increase in carrier depletion with increasing porosity, together with the complex structure and morphology of porous Si, are at the origin of complex energy filtering and phonon drag effects. All the above contribute to the observed anomalous behaviour of thermopower as a function of porosity and will be discussed.

  10. High Seebeck Coefficient of Porous Silicon: Study of the Porosity Dependence.

    PubMed

    Valalaki, Katerina; Benech, Philippe; Galiouna Nassiopoulou, Androula

    2016-12-01

    In-plane Seebeck coefficient of porous Si free-standing membranes of different porosities was accurately measured at room temperature. Quasi-steady-state differential Seebeck coefficient method was used for the measurements. A detailed description of our home-built setup is presented. The Seebeck coefficient was proved to increase with increasing porosity up to a maximum of ~1 mV/K for the ~50 % porosity membrane, which is more than a threefold increase compared to the starting highly doped bulk c-Si substrate. By further increasing porosity and after a maximum is reached, the Seebeck coefficient sharply decreases and stabilizes at ~600 μV/K. The possible mechanisms that determine this behaviour are discussed, supported by structural characterization and photoluminescence measurements. The decrease in nanostructure size and increase in carrier depletion with increasing porosity, together with the complex structure and morphology of porous Si, are at the origin of complex energy filtering and phonon drag effects. All the above contribute to the observed anomalous behaviour of thermopower as a function of porosity and will be discussed. PMID:27075343

  11. Large Seebeck coefficient in frustrated doped Mott insulators

    NASA Astrophysics Data System (ADS)

    Arsenault, Louis-François; Shastry, B. Sriram; Sémon, Patrick; Tremblay, André-Marie

    2011-03-01

    Since calculations based on the standard Kubo formula have proven extremely difficult for electric and thermal transport, Shastry and co-workers suggested two novel approximate ways to obtain the thermopower (S) in interacting systems. One method is based on the high-frequency limit. The other, based on ideas of Kelvin, is purely thermodynamical. With these we study the Hubbard model on a 3d FCC lattice, a frustrated lattice. The high dimensionality of the problem justifies the use of dynamical mean field theory (DMFT). CTQMC in the hybridization expansion and the fast IPT are the impurity solver. The Seebeck coefficient is obtained as a function of doping and temperature for different U. Within DMFT, vertex corrections vanish for transports coefficients, hence the bubble suffices. This enables us to further assess how both approximate methods compare with each other and with the DC Kubo approach. At low T, results can be interpreted in terms of effective Fermi temperatures and carrier number.

  12. Microchip for the Measurement of Seebeck Coefficients of Single Nanowires

    NASA Astrophysics Data System (ADS)

    Völklein, F.; Schmitt, M.; Cornelius, T. W.; Picht, O.; Müller, S.; Neumann, R.

    2009-07-01

    Bismuth nanowires were electrochemically grown in ion track-etched polycarbonate membranes. Micromachining and microlithography were employed to realize a newly developed microchip for Seebeck coefficient measurements on individual nanowires. By anisotropic etching of a (100) Si wafer, an 800-nm-thick SiO2/Si3N4 membrane was prepared in the chip center. The low thermal conductivity of the membrane is crucial to obtain the required temperature difference Δ T along the nanowire. The wire is electrically contacted to thin metal pads which are patterned by a new method of microscopic exposure of photoresist and a lift-off process. A Δ T between the two pairs of contact pads, located on the membrane, is established by a thin-film heater. Applying the known Seebeck coefficient of a reference film, the temperature difference at this gap is determined. Using Δ T and the measured Seebeck voltage U of the nanowire, its Seebeck coefficient can be calculated.

  13. System to Measure Thermal Conductivity and Seebeck Coefficient for Thermoelectrics

    NASA Technical Reports Server (NTRS)

    Kim, Hyun-Jung; Skuza, Jonathan R.; Park, Yeonjoon; King, Glen C.; Choi, Sang H.; Nagavalli, Anita

    2012-01-01

    The Seebeck coefficient, when combined with thermal and electrical conductivity, is an essential property measurement for evaluating the potential performance of novel thermoelectric materials. However, there is some question as to which measurement technique(s) provides the most accurate determination of the Seebeck coefficient at elevated temperatures. This has led to the implementation of nonstandardized practices that have further complicated the confirmation of reported high ZT materials. The major objective of the procedure described is for the simultaneous measurement of the Seebeck coefficient and thermal diffusivity within a given temperature range. These thermoelectric measurements must be precise, accurate, and reproducible to ensure meaningful interlaboratory comparison of data. The custom-built thermal characterization system described in this NASA-TM is specifically designed to measure the inplane thermal diffusivity, and the Seebeck coefficient for materials in the ranging from 73 K through 373 K.

  14. Calculation of Phonon Conductivity and Seebeck Coefficient in Cu-Ni Alloy

    NASA Astrophysics Data System (ADS)

    Konishi, Yusuke; Asai, Yoshihiro

    2015-03-01

    In recent years, thermoelectric materials have been attracting a lot of attention because they are expected to be applied for utilization of waste heat. Many kinds of materials are studied for this purpose; semiconductors, alloys, organic materials, etc. In 2010, a giant Peltier effect was observed in a Cu-Ni/Au junction. It is considered that this giant Peltier effect is caused by nano-scale phase separation formed in the sputtering process. Although this material is a great candidate for a thermoelectric material, we need to find the condition for a large thermoelectric coefficient that requires a large Seebeck coefficient, large electric conductivity, and small phonon conductivity. We calculated phonon conductivity in Cu-Ni alloy by using nonequilibrium molecular dynamics simulation and calculated Seebeck coefficients via ab-initio methods.

  15. Identification of a positive-Seebeck-coefficient exohedral fullerene

    NASA Astrophysics Data System (ADS)

    Almutlaq, Nasser; Al-Galiby, Qusiy; Bailey, Steven; Lambert, Colin J.

    2016-07-01

    If fullerene-based thermoelectricity is to become a viable technology, then fullerenes exhibiting both positive and negative Seebeck coefficients are needed. C60 is known to have a negative Seebeck coefficient and therefore in this paper we address the challenge of identifying a positive-Seebeck-coefficient fullerene. We investigated the thermoelectric properties of single-molecule junctions of the exohedral fullerene C50Cl10 connected to gold electrodes and found that it indeed possesses a positive Seebeck coefficient. Furthermore, in common with C60, the Seebeck coefficient can be increased by placing more than one C50Cl10 in series. For a single C50Cl10, we find S = +8 μV K-1 and for two C50Cl10's in series we find S = +30 μV K-1. We also find that the C50Cl10 monomer and dimer have power factors of 0.5 × 10-5 W m-1 K-2 and 6.0 × 10-5 W m-1 K-2 respectively. These results demonstrate that exohedral fullerenes provide a new class of thermoelectric materials with desirable properties, which complement those of all-carbon fullerenes, thereby enabling the boosting of the thermovoltage in all-fullerene tandem structures.If fullerene-based thermoelectricity is to become a viable technology, then fullerenes exhibiting both positive and negative Seebeck coefficients are needed. C60 is known to have a negative Seebeck coefficient and therefore in this paper we address the challenge of identifying a positive-Seebeck-coefficient fullerene. We investigated the thermoelectric properties of single-molecule junctions of the exohedral fullerene C50Cl10 connected to gold electrodes and found that it indeed possesses a positive Seebeck coefficient. Furthermore, in common with C60, the Seebeck coefficient can be increased by placing more than one C50Cl10 in series. For a single C50Cl10, we find S = +8 μV K-1 and for two C50Cl10's in series we find S = +30 μV K-1. We also find that the C50Cl10 monomer and dimer have power factors of 0.5 × 10-5 W m-1 K-2 and 6.0 × 10-5 W m-1

  16. Nanoscale Thermoelectrics: A Study of the Absolute Seebeck Coefficient of Thin Films

    NASA Astrophysics Data System (ADS)

    Mason, Sarah J.

    measure, S, as a function of temperature using a micro-machined thermal isolation platform consisting of a suspended, patterned SiN membrane. By measuring a series of thicknesses of metallic films up to the infinitely thin film limit, in which the electrical resistivity is no longer decreasing with increasing film thickness, but still not at bulk values, along with the effective electron mean free path, we are able to show the contribution of the leads needed to measure this property. Having a comprehensive understanding of the background contribution we are able to determine the absolute Seebeck coefficient of a wide variety of thin films. The nature of the design of the SiN membrane also allows the ability to accurately and directly measure thermal and electrical transport of the thin films yielding a comprehensive measurement of the three quantities that characterize a material's efficiency. This can serve to further the development of thermoelectric materials through precise measurements of the material properties that dictate efficiency.

  17. Spin Seebeck measurements of current-induced switching in YIG

    NASA Astrophysics Data System (ADS)

    Bartell, Jason; Jermain, Colin; Aradhya, Sriharsha; Wang, Hailong; Buhrman, Robert; Yang, Fengyuan; Ralph, Daniel; Fuchs, Gregory

    Quantifying spin torques generated at the interface between a normal metal (NM) and a ferromagnetic insulator (FI) is an important step in understanding the spin hall effect without charge transport. Measuring magnetization in NM/FI devices is challenging, however, because both magnetoresistive and magneto-optical signals are tiny in thin-film bilayers. We show that a promising alternative measurement approach is the use of picosecond thermal gradients to study spin torques in Pt/Yttrium Iron Garnet (YIG) bilayers. Recently, we demonstrated the application of heat to stroboscopically transduce a local magnetic moment into an electrical signal via the time resolved anomalous Nernst effect (TRANE) in ferromagnetic metals. Using a similar geometry the spin Seebeck effect of YIG combined with the inverse spin Hall effect of Pt enables measurement of local magnetization. Here we describe our study using this technique to study current-induced switching in Pt/YIG with sub-10 nm thick YIG films We acknowledge support from AFOSR.

  18. Identification of a positive-Seebeck-coefficient exohedral fullerene.

    PubMed

    Almutlaq, Nasser; Al-Galiby, Qusiy; Bailey, Steven; Lambert, Colin J

    2016-07-14

    If fullerene-based thermoelectricity is to become a viable technology, then fullerenes exhibiting both positive and negative Seebeck coefficients are needed. C60 is known to have a negative Seebeck coefficient and therefore in this paper we address the challenge of identifying a positive-Seebeck-coefficient fullerene. We investigated the thermoelectric properties of single-molecule junctions of the exohedral fullerene C50Cl10 connected to gold electrodes and found that it indeed possesses a positive Seebeck coefficient. Furthermore, in common with C60, the Seebeck coefficient can be increased by placing more than one C50Cl10 in series. For a single C50Cl10, we find S = +8 μV K(-1) and for two C50Cl10's in series we find S = +30 μV K(-1). We also find that the C50Cl10 monomer and dimer have power factors of 0.5 × 10(-5) W m(-1) K(-2) and 6.0 × 10(-5) W m(-1) K(-2) respectively. These results demonstrate that exohedral fullerenes provide a new class of thermoelectric materials with desirable properties, which complement those of all-carbon fullerenes, thereby enabling the boosting of the thermovoltage in all-fullerene tandem structures. PMID:27357101

  19. High Pressure Seebeck Coefficient Measurements Using Paris-Edinburgh Cell

    NASA Astrophysics Data System (ADS)

    Baker, Jason; Kumar, Ravhi; Park, Changyong; Kenney-Benson, Curtis; Velisavljevic, Nenad; Hipsec; Department Of Physics, University Of Nevada, Las Vegas Collaboration; Hpcat, Geophysical Laboratory, Carnegie Institution Of Washington Collaboration; Shock; Detonation Physics Group, Los Alamos National Laboratory Collaboration

    We have developed a new type of sample cell assembly for the Paris-Edinburgh (PE) type large volume press for simultaneous x-ray diffraction, electrical resistance, and thermal measurements at high pressures. We demonstrate the feasibility of performing in situ measurements of the Seebeck coefficient over a broad range of pressure-temperature conditions by observing the well-known solid-solid and solid-melt transitions of bismuth (Bi) up to 3GPa and 450 K. We observed a gradual increase in the Seebeck coefficient which becomes positive during transition to the Bi - II phase. Also, we have performed successful Seebeck coefficient measurements on the thermoelectric material PbTe. This new capability enables us to directly correlate pressure-induced structural phase transitions to electrical and thermal properties.

  20. Seebeck Coefficient Metrology: Do Contemporary Protocols Measure Up?

    NASA Astrophysics Data System (ADS)

    Martin, Joshua; Wong-Ng, Winnie; Green, Martin L.

    2015-06-01

    Comparative measurements of the Seebeck coefficient are challenging due to the diversity of instrumentation and measurement protocols. With the implementation of standardized measurement protocols and the use of Standard Reference Materials (SRMs®), for example, the recently certified National Institute of Standards and Technology (NIST) SRM® 3451 ``Low Temperature Seebeck Coefficient Standard (10-390 K)'', researchers can reliably analyze and compare data, both intra- and inter-laboratory, thereby accelerating the development of more efficient thermoelectric materials and devices. We present a comparative overview of commonly adopted Seebeck coefficient measurement practices. First, we examine the influence of asynchronous temporal and spatial measurement of electric potential and temperature. Temporal asynchronicity introduces error in the absolute Seebeck coefficient of the order of ≈10%, whereas spatial asynchronicity introduces error of the order of a few percent. Second, we examine the influence of poor thermal contact between the measurement probes and the sample. This is especially critical at high temperature, wherein the prevalent mode of measuring surface temperature is facilitated by pressure contact. Each topic will include the comparison of data measured using different measurement techniques and using different probe arrangements. We demonstrate that the probe arrangement is the primary limit to high accuracy, wherein the Seebeck coefficients measured by the 2-probe arrangement and those measured by the 4-probe arrangement diverge with the increase in temperature, approaching ≈14% at 900 K. Using these analyses, we provide recommended measurement protocols to guide members of the thermoelectric materials community in performing more accurate measurements and in evaluating more comprehensive uncertainty limits.

  1. The Seebeck Coefficient and Phonon Drag in Silicon

    SciTech Connect

    Mahan, Gerald; Lindsay, Lucas R.; Broido, David

    2014-12-29

    We present a theory of the phonon-drag Seebeck coe cient in nondegenerate semiconductors, and apply it to silicon for temperatures 30 < T < 300K. Our calculation uses only parameters from the literature, and previous calculations of the phonon lifetime. We nd excellent agreement with the measurements of Geballe and Hull [Phys.Rev. 98, 940 (1955)]. The phonon-drag term dominates at low temperature, and shows an important dependence on the dimensions of the experimental sample.

  2. Theory of asymmetric and negative differential magnon tunneling under temperature bias: Towards a spin Seebeck diode and transistor

    NASA Astrophysics Data System (ADS)

    Ren, Jie; Zhu, Jian-Xin

    2013-09-01

    We study the nonequilibrium transport for the asymmetric and negative differential magnon tunneling driven by temperature bias. We demonstrate that the many-body magnon interaction that makes the magnonic spectrum temperature-dependent is the crucial factor for the emergence of rectification and negative differential spin Seebeck effects in magnon tunneling junctions. When magnonic junctions have temperature-dependent density of states, reversing the temperature bias is able to give asymmetric spin currents and increasing temperature bias could give an anomalously decreasing magnonic spin current. We show that these properties are relevant for building spin Seebeck diodes and transistors, which could play important roles in controlling information and energy in magnonics and spin caloritronics.

  3. Design for a spin-Seebeck diode based on two-dimensional materials

    NASA Astrophysics Data System (ADS)

    Fu, Hua-Hua; Wu, Dan-Dan; Gu, Lei; Wu, Menghao; Wu, Ruqian

    2015-07-01

    Studies of the spin-Seebeck effect (SSE) are very important for the development of fundamental science and novel low-power-consumption technologies. The spin-Seebeck diode (SSD), in which the spin current can be driven by a forward temperature gradient but not by a reverse temperature gradient, is a key unit in spin caloritronic devices. Here, we propose a SSD design using two-dimensional (2D) materials such as silicene and phosphorene nanoribbons as the source and drain. Due to their unique band structures and magnetic states, thermally driven spin-up and spin-down currents flow in opposite directions. This mechanism is different from that of the previous one, which uses two permalloy circular disks [Phys. Rev. Lett. 112, 047203 (2014), 10.1103/PhysRevLett.112.047203], and the SSD in our design can be easily integrated with gate voltage control. Since the concept of this design is rather general and applicable to many 2D materials, it is promising for the realization and exploitation of SSDs in nanodevices.

  4. A microprobe technique for simultaneously measuring thermal conductivity and Seebeck coefficient of thin films

    NASA Astrophysics Data System (ADS)

    Zhang, Yanliang; Hapenciuc, Claudiu L.; Castillo, Eduardo E.; Borca-Tasciuc, Theodorian; Mehta, Rutvik J.; Karthik, Chinnathambi; Ramanath, Ganpati

    2010-02-01

    We demonstrate a microprobe technique that can simultaneously measure thermal conductivity κ and Seebeck coefficient α of thin films. In this technique, an alternative current joule-heated V-shaped microwire that serves as heater, thermometer and voltage electrode, locally heats the thin film when contacted with the surface. The κ is extracted from the thermal resistance of the microprobe and α from the Seebeck voltage measured between the probe and unheated regions of the film by modeling heat transfer in the probe, sample and their contact area, and by calibrations with standard reference samples. Application of the technique on sulfur-doped porous Bi2Te3 and Bi2Se3 films reveals α =-105.4 and 1.96 μV/K, respectively, which are within 2% of the values obtained by independent measurements carried out using microfabricated test structures. The respective κ values are 0.36 and 0.52 W/mK, which are significantly lower than the bulk values due to film porosity, and are consistent with effective media theory. The dominance of air conduction at the probe-sample contact area determines the microscale spatial resolution of the technique and allows probing samples with rough surfaces.

  5. Seebeck rectification enabled by intrinsic thermoelectrical coupling in magnetic tunneling junctions.

    PubMed

    Zhang, Z H; Gui, Y S; Fu, L; Fan, X L; Cao, J W; Xue, D S; Freitas, P P; Houssameddine, D; Hemour, S; Wu, K; Hu, C-M

    2012-07-20

    An intrinsic thermoelectric coupling effect in the linear response regime of magnetic tunneling junctions (MTJ) is reported. In the dc response, it leads to a nonlinear correction to Ohm's law. Dynamically, it enables a novel Seebeck rectification and second harmonic generation, which apply for a broad frequency range and can be magnetically controlled. A phenomenological model on the footing of the Onsager reciprocal relation and the principle of energy conservation explains very well the experimental results obtained from both dc and frequency-dependent transport measurements performed up to GHz frequencies. Our work refines previous understanding of magnetotransport and microwave rectification in MTJs. It forms a new foundation for utilizing spin caloritronics in high-frequency applications. PMID:22861893

  6. Conductivities and Seebeck Coefficients of Boron Carbides: ''Softening-Bipolaron'' Hopping

    SciTech Connect

    ASELAGE,TERRENCE L.; EMIN,DAVID JACOB; MCCREADY,STEVEN S.

    2000-07-20

    The most conspicuous feature of boron carbides' electronic transport properties is their having both high carrier densities and large Seebeck coefficients. The magnitudes and temperature dependencies of the Seebeck coefficients are consistent with large contributions from softening bipolarons: singlet bipolarons whose stabilization is significantly affected by their softening of local vibrations. Boron carbides' high carrier densities, small activation energies for hopping ({approx} 0.16 eV), and anomalously large Seebeck coefficients combine with their low, glass-like thermal conductivities to make them unexpectedly efficient high-temperature thermoelectrics.

  7. Characterization of thermoelectric devices by laser induced Seebeck electromotive force (LIS-EMF) measurement

    NASA Astrophysics Data System (ADS)

    Patiño Lopez, Luis-David; Dilhaire, Stefan; Grauby, Stéphane; Amine Salhi, M.; Ezzahri, Younès; Claeys, Wilfrid; Batsale, Jean-Christophe

    2005-05-01

    An in-depth study related to a new method of characterizing properties in thermoelectrics is proposed in this paper. This technique is appropriate for single or multi-layered thermoelectric devices. A modulated laser beam is used as a heater in order to generate a Seebeck electromotive force (EMF). The laser beam, line shaped, can be focused at any location along the sample surface, allowing spatially resolved measurements. Seebeck EMF measurements, associated with a versatile model based on the thermal quadrupoles method, allow determination of the sample Seebeck EMF profile and identifying of the sample thermal contact resistances, and should be useful for identification of devices and material thermoelectric properties.

  8. Thermal study of PN thermoelectric couple by laser induced Seebeck EMF measurement

    NASA Astrophysics Data System (ADS)

    Patiño-Lopez, Luis-David; Amine Salhi, M.; Dilhaire, Stefan; Grauby, Stéphane; Rampnoux, Jean-Michel; Jorez, Sébastien; Claeys, Wilfrid

    2004-03-01

    We propose in this paper an in-depth study of a method, both experimental and theoretical, for the determination of thermoelectric properties, in single, or multi-layered thermoelectric devices. We use a modulated laser beam as a heater in order to generate a thermally induced Seebeck EMF. The laser beam, line shaped, can be focused at any location along the sample surface, allowing spatially resolved measurements. Seebeck EMF measurements, associated with a versatile modeling method based on the thermal quadrupoles, allow determining sample Seebeck EMF profile. We contemplate to apply this technique to thermal and thermoelectric properties identification.

  9. Multifold Seebeck increase in RuO{sub 2} films by quantum-guided lanthanide dilute alloying

    SciTech Connect

    Music, Denis Basse, Felix H.-U.; Schneider, Jochen M.; Han, Liang; Borca-Tasciuc, Theo; Devender; Gengler, Jamie J.; Voevodin, Andrey A.; Ramanath, Ganpati

    2014-02-03

    Ab initio predictions indicating that alloying RuO{sub 2} with La, Eu, or Lu can increase the Seebeck coefficient α manifold due to quantum confinement effects are validated in sputter-deposited La-alloyed RuO{sub 2} films showing fourfold α increase. Combinatorial screening reveals that α enhancement correlates with La-induced lattice distortion, which also decreases the thermal conductivity twentyfold, conducive for high thermoelectric figures of merit. These insights should facilitate the rational design of high efficiency oxide-based thermoelectrics through quantum-guided alloying.

  10. Colossal Seebeck Coefficient of Hopping Electrons in (TMTSF) 2 PF6

    NASA Astrophysics Data System (ADS)

    Machida, Yo; Lin, Xiao; Kang, Woun; Izawa, Koichi; Behnia, Kamran

    2016-02-01

    We report on a study of the Seebeck coefficient and resistivity in the quasi-one-dimensional conductor (TMTSF) 2 PF6 extended deep into the spin-density-wave state. The metal-insulator transition at TSDW=12 K leads to a reduction in carrier concentration by 7 orders of magnitude. Below 1 K, charge transport displays the behavior known as variable range hopping. Until now, the Seebeck response of electrons in this regime has barely been explored and is even less understood. We find that, in this system, residual carriers, hopping from one trap to another, generate a Seebeck coefficient as large as 400 kB/e . The results provide the first solid evidence for a long-standing prediction according to which hopping electrons in the presence of the Coulomb interaction can generate a sizable Seebeck coefficient in the zero-temperature limit.

  11. Dependence of Seebeck coefficient on a load resistance and energy conversion efficiency in a thermoelectric composite

    SciTech Connect

    Yamashita, Osamu Odahara, Hirotaka; Ochi, Takahiro; Satou, Kouji

    2007-10-02

    The thermo-emf {delta}V and current {delta}I generated by imposing the alternating temperature gradients (ATG) at a period of T and the steady temperature gradient (STG) on a thermoelectric (TE) composite were measured as a function of t, where t is the lapsed time and T was varied from 60 to or {infinity} s. The STG and ATG were produced by imposing steadily and alternatively a source voltage V in the range from 1.0 to 4.0 V on two Peltier modules sandwiching a composite. {delta}T, {delta}V, {delta}I and V{sub P} oscillate at a period T and their waveforms vary significantly with a change of T, where {delta}V and V{sub P} are the voltage drops in a load resistance R{sub L} and in resistance R{sub P} of two modules. The resultant Seebeck coefficient |{alpha}| = |{delta}V|/{delta}T of a composite under the STG was found to be expressed as |{alpha}| = |{alpha}{sub 0}|(1 - R{sub comp}/R{sub T}), where R{sub T} is the total resistance of a circuit for measuring the output signals and R{sub comp} is the resistance of a composite. The effective generating power {delta}W{sub eff} has a local maximum at T = 960 s for the p-type composite and at T = 480 s for the n-type one. The maximum energy conversion efficiency {eta} of the p- and n-type composites under the ATG produced by imposing a voltage of 4.0 V at an optimum period were 0.22 and 0.23% at {delta}T{sub eff} = 50 K, respectively, which are 42 and 43% higher than those at {delta}T = 42 K under the STG. These maximum {eta} for a TE composite sandwiched between two Peltier modules, were found to be expressed theoretically in terms of R{sub P}, R{sub T}, R{sub L}, {alpha}{sub P} and {alpha}, where {alpha}{sub P} and {alpha} are the resultant Seebeck coefficients of Peltier modules and a TE composite.

  12. A Study of the Measurement of Seebeck Coefficient of SiGe

    NASA Technical Reports Server (NTRS)

    Heung, King Yi

    2005-01-01

    In 1821 German Physicist Thomas J. Seebeck discovered that heat could be converted into electricity when a temperature difference was applied across two points on a material. Theoretically, the generated voltage has a directly proportional relationship with the temperature difference. This relationship is the Seebeck coefficient that scientists always referred to when determining the efficiency of a thermoelectricity convention. In our experiments, however, hysteresis loops appeared when we plotted voltage against temperature difference, and the measured Seebeck appeared differently when the measurements were run under vacuum, air, and helium gas. Measurements were done by using a low-frequency AC measuring method. By simulating the experimental setup into a; thermal circuit, we found that the loop and inconsistency in measuring Seebeck coefficient could be explained by studying the behaviors of a RC circuit in a thermal sense. Under vacuum, the gap of the hysteresis loop can be largely eliminated if the time period of the temperature difference increased up to 4800s. The trend of the variations in measuring Seebeck coefficients in different environments can also be predicted by using different thermal circuit models.

  13. Characterization of Lorenz number with Seebeck coefficient measurement

    SciTech Connect

    Kim, Hyun-Sik; Gibbs, Zachary M.; Tang, Yinglu; Wang, Heng; Snyder, G. Jeffrey

    2015-04-01

    In analyzing zT improvements due to lattice thermal conductivity (κ{sub L}) reduction, electrical conductivity (σ) and total thermal conductivity (κ{sub Total}) are often used to estimate the electronic component of the thermal conductivity (κ{sub E}) and in turn κ{sub L} from κ{sub L} = ∼ κ{sub Total} − LσT. The Wiedemann-Franz law, κ{sub E} = LσT, where L is Lorenz number, is widely used to estimate κ{sub E} from σ measurements. It is a common practice to treat L as a universal factor with 2.44 × 10{sup −8} WΩK{sup −2} (degenerate limit). However, significant deviations from the degenerate limit (approximately 40% or more for Kane bands) are known to occur for non-degenerate semiconductors where L converges to 1.5 × 10{sup −8} WΩK{sup −2} for acoustic phonon scattering. The decrease in L is correlated with an increase in thermopower (absolute value of Seebeck coefficient (S)). Thus, a first order correction to the degenerate limit of L can be based on the measured thermopower, |S|, independent of temperature or doping. We propose the equation: L=1.5+exp[−(|S|)/(116) ] (where L is in 10{sup −8} WΩK{sup −2} and S in μV/K) as a satisfactory approximation for L. This equation is accurate within 5% for single parabolic band/acoustic phonon scattering assumption and within 20% for PbSe, PbS, PbTe, Si{sub 0.8}Ge{sub 0.2} where more complexity is introduced, such as non-parabolic Kane bands, multiple bands, and/or alternate scattering mechanisms. The use of this equation for L rather than a constant value (when detailed band structure and scattering mechanism is not known) will significantly improve the estimation of lattice thermal conductivity.

  14. A possible origin for the colossally large Seebeck coefficient in FeSb2

    NASA Astrophysics Data System (ADS)

    Takahashi, Hidefumi; Okazaki, Ryuji; Terasaki, Ichiro; Yasui, Yukio

    2014-03-01

    Narrow-gap semiconductor FeSb2 has attracted interest because of the recent observation of a colossal Seebeck coefficient S ~= - 45 mV/K at 10 K.[A. Bentien et al ., EPL 80, 17008 (2007).] This compound has a small energy gap Δ ~ 5 meV and | S | rapidly increases below 40 K, suggesting that Δ is formed by an unusual mechanism such as a strong electron correlation. However, the reported maximum values of S are remarkably different from sample to sample, ranging from - 500 μV/K to - 45 mV/K. We report a systematic study of ppm-level impurity effects of magnetic and transport properties with single crystals.[H. Takahashi et al ., JPSJ. 80, 054708 (2011).] A purest sample has a small carrier concentration (<1016 cm-3 below 30 K) and a large S (- 1400 μV/K at 20 K), indicating that the large S predominantly comes from the small carrier density. Moreover, we have measured the magnetic field dependence of transport properties of the purest crystal to investigate the relation between the electronic states and transport properties. We successfully explain the results in terms of an extrinsic semiconductor with ppm-level impurities, suggesting that the large S arises from the low carrier concentration with a phonon-drag

  15. Thermal Modeling and Analysis of a Sub-Compact Seebeck Furnace

    NASA Technical Reports Server (NTRS)

    Wang, Francis C.; Peters, Palmer; Rose, M. Franklin (Technical Monitor)

    2001-01-01

    The Sub-Compact Seebeck Furnace (SCSF) is a third generation furnace designed as an experimental facility to study the phenomena of undercooling associated with directional solidification. It is intended to provide a double peak temperature profile along the axial direction with gradient zones at each end. By keeping the temperature in the central portion above the melting point of the sample, and cooling the ends of the furnace, a solid/liquid (S/L) interface can be maintained in each one of the gradient zones. A motorized motion control provides a motion to one-half of the furnace. The undercooling associated with the interface being directionally solidified can thus be studied. Modeling of the temperature profile is important to help assure that the furnace design provides the correct thermal characteristics. The furnace is designed with two halves that telescope. Results of thermal analysis based on an analytical solution using simple assumptions will be presented. The resulting temperature profile will show the salient features of the desired thermal profile and provide the general directions for thermal design. Experimental results will be used to compare with the analytical profile. Approach for numerical modeling to provide more detailed information such as two-dimensional effects will be discussed.

  16. Carbon nanotubes enhanced Seebeck coefficient and power factor of rutile TiO2.

    PubMed

    Lai, Yao-Cheng; Tsai, Hsin-Jung; Hung, Chia-I; Fujishiro, Hiroyuki; Naito, Tomoyuki; Hsu, Wen-Kuang

    2015-03-28

    The Seebeck coefficient, according to Ioffe's approximation, is inversely proportional to carrier density and decreases with doping. Herein, we find that the incorporation of multi-walled carbon nanotubes into rutile TiO2 improves the electrical conductivity and Seebeck coefficient at a low filling fraction of tubes; moreover, the former was due to the lengthening of the mean free path and doping modified carrier mobility for the latter. Tube-oxide mixing also causes significant phonon drag at the interfaces and the reduced thermal conductivity was verified by the promoted figure of merit. PMID:25729788

  17. Seebeck coefficients in ionic liquids--prospects for thermo-electrochemical cells.

    PubMed

    Abraham, Theodore J; MacFarlane, Douglas R; Pringle, Jennifer M

    2011-06-14

    Measurement of Seebeck coefficients in a range of ionic liquids (ILs) suggests that these electrolytes could enable the development of thermoelectric devices to generate electrical energy from low-grade heat in the 100-150 °C range. PMID:21544302

  18. Seebeck and thermal conductivity analysis in amorphous/crystalline {beta}-K{<_2}Bi{<_8}Se{<_13} nanocomposite materials.

    SciTech Connect

    Kyratsi, Th.; Hatzikraniotis, E.; Ioannou, M.; Chung, D. Y.; Tsiaoussis, I.

    2011-01-01

    In this work, ball milling is applied on {beta}-K{sub 2}Bi{sub 8}Se{sub 13} compounds in order to explore the potential of the process for the fabrication of nano-based material. Polycrystalline {beta}-K{sub 2}Bi{sub 8}Se{sub 13}, synthesized from melt, was ball milled under inert atmosphere. Powder x-ray diffraction showed a significantly increased disorder with ball milling time. TEM studies confirmed the presence of nanocrystalline material in an amorphous matrix, suggesting the development of crystalline/amorphous {beta}-K{sub 2}Bi{sub 8}Se{sub 13} nanocomposite material via ball milling process. Seebeck coefficient and thermal conductivity were analyzed based on the effective medium theory and show a significant contribution of a nanocrystalline phase.

  19. Instrument for stable high temperature Seebeck coefficient and resistivity measurements under controlled oxygen partial pressure

    SciTech Connect

    Ihlefeld, Jon F.; Brown-Shaklee, Harlan James; Sharma, Peter Anand

    2015-04-28

    The transport properties of ceramic materials strongly depend on oxygen activity, which is tuned by changing the partial oxygen pressure (pO2) prior to and during measurement. Within, we describe an instrument for highly stable measurements of Seebeck coefficient and electrical resistivity at temperatures up to 1300 K with controlled oxygen partial pressure. An all platinum construction is used to avoid potential materials instabilities that can cause measurement drift. Two independent heaters are employed to establish a small temperature gradient for Seebeck measurements, while keeping the average temperature constant and avoiding errors associated with pO2-induced drifts in thermocouple readings. Oxygen equilibrium is monitored using both an O2 sensor and the transient behavior of the resistance as a proxy. A pO2 range of 10-25–100 atm can be established with appropriate gas mixtures. Seebeck measurements were calibrated against a high purity platinum wire, Pt/Pt–Rh thermocouple wire, and a Bi2Te3 Seebeck coefficient Standard Reference Material. To demonstrate the utility of this instrument for oxide materials we present measurements as a function of pO2 on a 1 % Nb-doped SrTiO3 single crystal, and show systematic changes in properties consistent with oxygen vacancy defect chemistry. Thus, an approximately 11% increase in power factor over a pO2 range of 10-19–10-8 atm at 973 K for the donor-doped single crystals is observed.

  20. Instrument for stable high temperature Seebeck coefficient and resistivity measurements under controlled oxygen partial pressure

    DOE PAGESBeta

    Ihlefeld, Jon F.; Brown-Shaklee, Harlan James; Sharma, Peter Anand

    2015-04-28

    The transport properties of ceramic materials strongly depend on oxygen activity, which is tuned by changing the partial oxygen pressure (pO2) prior to and during measurement. Within, we describe an instrument for highly stable measurements of Seebeck coefficient and electrical resistivity at temperatures up to 1300 K with controlled oxygen partial pressure. An all platinum construction is used to avoid potential materials instabilities that can cause measurement drift. Two independent heaters are employed to establish a small temperature gradient for Seebeck measurements, while keeping the average temperature constant and avoiding errors associated with pO2-induced drifts in thermocouple readings. Oxygen equilibriummore » is monitored using both an O2 sensor and the transient behavior of the resistance as a proxy. A pO2 range of 10-25–100 atm can be established with appropriate gas mixtures. Seebeck measurements were calibrated against a high purity platinum wire, Pt/Pt–Rh thermocouple wire, and a Bi2Te3 Seebeck coefficient Standard Reference Material. To demonstrate the utility of this instrument for oxide materials we present measurements as a function of pO2 on a 1 % Nb-doped SrTiO3 single crystal, and show systematic changes in properties consistent with oxygen vacancy defect chemistry. Thus, an approximately 11% increase in power factor over a pO2 range of 10-19–10-8 atm at 973 K for the donor-doped single crystals is observed.« less

  1. Measurements of the Seebeck coefficient of thermoelectric materials by an ac method

    SciTech Connect

    Goto, T.; Li, J.H.; Hirai, T.; Maeda, Y.; Kato, R.; Maesono, A.

    1997-03-01

    An ac method for measurement of the Seebeck coefficient was developed. Specimens were heated periodically at frequencies in the range 0.2--10 Hz using a semiconductor laser. The small temperature increase and the resultant thermoelectric power were measured with a Pt-Pt 13% Rh thermocouple (25 {micro}m in diameter) through a lock-in amplifier. The Seebeck coefficient of a Pt{sub 90}Rh{sub 10} foil measured by the ac method was in agreement with that obtained from the standard table. The optimum frequency and specimen thickness for the ac method were 0.2 Hz and 0.1--0.2 mm, respectively. The Seebeck coefficients of silicon single crystal and several thermoelectric semiconductors (Si{sub 80}Ge{sub 20}, PbTc, FeSi{sub 2}, SiB{sub 14}) measured by the ac method agreed with those measured by a conventional dc method in the temperature range between room temperature and 1200 K. The time needed for each measurement was less than a few tens of minutes, significantly shorter than that for a conventional dc method.

  2. Electrical Conductivity, Thermal Behavior, and Seebeck Coefficient of Conductive Films for Printed Thermoelectric Energy Harvesting Systems

    NASA Astrophysics Data System (ADS)

    Ankireddy, Krishnamraju; Menon, Akanksha K.; Iezzi, Brian; Yee, Shannon K.; Losego, Mark D.; Jur, Jesse S.

    2016-07-01

    Printed electronics is being explored as a rapid, facile means for manufacturing thermoelectric generators (TEGs) that can recover useful electrical energy from waste heat. This work examines the relevant electrical conductivity, thermal resistance, thermovoltage, and Seebeck coefficient of printed films for use in such printed flexible TEGs. The thermoelectric performance of TEGs printed using commercially relevant nickel, silver, and carbon inks is evaluated. The microstructure of the printed films is investigated to better understand why the electrical conductivity and Seebeck coefficient are degraded. Thermal conduction is shown to be relatively insensitive to the type of metalized coating and nearly equivalent to that of an uncoated polymer substrate. Of the commercially available conductive ink materials examined, carbon-nickel TEGs are shown to exhibit the highest thermovoltage, with a value of 10.3 μV/K. However, silver-nickel TEGs produced the highest power generation of 14.6 μW [from 31 junctions with temperature difference (ΔT) of 113°C] due to their low electrical resistance. The voltage generated from the silver-nickel TEG was stable under continuous operation at 275°C for 3 h. We have also demonstrated that, after a year of storage in ambient conditions, these devices retain their performance. Notably, the electrical conductivity and Seebeck coefficient measured for individual materials were consistent with those measured from actual printed TEG device structures, validating the need for further fundamental materials characterization to accelerate flexible TEG device optimization.

  3. Monitoring the embrittlement of reactor pressure vessel steels by using the Seebeck coefficient

    NASA Astrophysics Data System (ADS)

    Niffenegger, M.; Leber, H. J.

    2009-06-01

    The degree of embrittlement of the reactor pressure vessel (RPV) limits the lifetime of nuclear power plants. Therefore, neutron irradiation-induced embrittlement of RPV steels demands accurate monitoring. Current federal legislation requires a surveillance program in which specimens are placed inside the RPV for several years before their fracture toughness is determined by destructive Charpy impact testing. Measuring the changes in the thermoelectric properties of the material due to irradiation, is an alternative and non-destructive method for the diagnostics of material embrittlement. In this paper, the measurement of the Seebeck coefficient ( K¯) of several Charpy specimens, made from two different grades of 22 NiMoCr 37 low-alloy steels, irradiated by neutrons with energies greater than 1 MeV, and fluencies ranging from 0 up to 4.5 × 10 19 neutrons per cm 2, are presented. Within this range, it was observed that K¯ increased by ≈500 nV/°C and a linear dependency was noted between K¯ and the temperature shift Δ T41 J of the Charpy energy vs. temperature curve, which is a measure for the embrittlement. We conclude that the change of the Seebeck coefficient has the potential for non-destructive monitoring of the neutron embrittlement of RPV steels if very precise measurements of the Seebeck coefficient are possible.

  4. Uncertainty Analysis of Seebeck Coefficient and Electrical Resistivity Characterization

    NASA Technical Reports Server (NTRS)

    Mackey, Jon; Sehirlioglu, Alp; Dynys, Fred

    2014-01-01

    In order to provide a complete description of a materials thermoelectric power factor, in addition to the measured nominal value, an uncertainty interval is required. The uncertainty may contain sources of measurement error including systematic bias error and precision error of a statistical nature. The work focuses specifically on the popular ZEM-3 (Ulvac Technologies) measurement system, but the methods apply to any measurement system. The analysis accounts for sources of systematic error including sample preparation tolerance, measurement probe placement, thermocouple cold-finger effect, and measurement parameters; in addition to including uncertainty of a statistical nature. Complete uncertainty analysis of a measurement system allows for more reliable comparison of measurement data between laboratories.

  5. Economical Route to Produce High Seebeck Coefficient Calcium Cobaltate for Bulk Thermoelectric Applications

    SciTech Connect

    Selig, Jiri; Lin, Sidney; Lin, Hua-Tay; Johnson, D Ray; Wang, Hsin

    2011-01-01

    Phase pure calcium cobaltate (Ca1.24Co1.62O3.86) was prepared by Self-propagating High-temperature Synthesis (SHS) followed by a short post heat treatment. Prepared powders were characterized by XRD for phase purity, and SEM for particle size and distribution. Temperature histories at the center and on the surface of reaction pellet during the SHS process were monitored and recorded. Particles size of synthesized powders was reduced using a planetary mill to increase its specific surface area. Electrical conductivity, thermal conductivity and Seebeck coefficient of the prepared power were measured and figure of merit was reported.

  6. Intermediate Valence Tuning and Seebeck Coefficient Optimization in Yb-based Low-Temperature Thermoelectric Materials

    NASA Astrophysics Data System (ADS)

    Lehr, Gloria; Morelli, Donald; Jin, Hyungyu; Heremans, Joseph

    2014-03-01

    Several Yb-based intermediate valence compounds have unique thermoelectric properties at low temperatures. These materials are interesting to study for niche applications such as cryogenic Peltier cooling of infrared sensors on satellites. Elements of different sizes, which form isostructural compounds, are used to form solid solutions creating a chemical pressure (smaller atoms - Sc) or relaxation (larger atoms - La) to alter the volume of the unit cell and thereby manipulate the average Yb valence. Magnetic susceptibility measurements show a strong correlation between the Seebeck coefficient and the ratio of trivalent to divalent Yb in these compounds. Two different Yb-based solid solution systems, Yb1-xScxAl2 and Yb1-xLaxCu2Si2, demonstrate that the concentration of Yb can be used to tune both the magnitude of the Seebeck coefficient as well as the temperature at which its absolute maximum occurs. This work is supported by Michigan State University and AFOSR-MURI ``Cryogenic Peltier Cooling'' Contract #FA9550-10-1-0533.

  7. Apparatus for measuring Seebeck coefficient and electrical resistivity of small dimension samples using infrared microscope as temperature sensor

    NASA Astrophysics Data System (ADS)

    Jaafar, W. M. N. Wan; Snyder, J. E.; Min, Gao

    2013-05-01

    An apparatus for measuring the Seebeck coefficient (α) and electrical resistivity (ρ) was designed to operate under an infrared microscope. A unique feature of this apparatus is its capability of measuring α and ρ of small-dimension (sub-millimeter) samples without the need for microfabrication. An essential part of this apparatus is a four-probe assembly that has one heated probe, which combines the hot probe technique with the Van der Pauw method for "simultaneous" measurements of the Seebeck coefficient and electrical resistivity. The repeatability of the apparatus was investigated over a temperature range of 40 °C-100 °C using a nickel plate as a standard reference. The results show that the apparatus has an uncertainty of ±4.9% for Seebeck coefficient and ±5.0% for electrical resistivity. The standard deviation of the apparatus against a nickel reference sample is -2.43 μVK-1 (-12.5%) for the Seebeck coefficient and -0.4 μΩ cm (-4.6%) for the electrical resistivity, respectively.

  8. Thermal Conductivity and Seebeck Coefficients of Icosahedral Boron Arsenide Films on Silicon Carbide

    SciTech Connect

    Y Gong; Y Zhang; M Dudley; Y Zhang; J Edgar; P Heard; M Kuball

    2011-12-31

    The thermal conductivity of icosahedral boron arsenide (B{sub 12}As{sub 2}) films grown on (0001) 6H-SiC substrates by chemical vapor deposition was studied by the 3{omega} technique. The room temperature thermal conductivity decreased from 27.0 to 15.3 W/m K as the growth temperature was decreased from 1450 to 1275 C. This is mainly attributed to the differences in the impurity concentration and microstructure, determined from secondary ion mass spectrometry and high resolution transmission electron microscopy, respectively. Callaway's theory was applied to calculate the temperature-dependent thermal conductivity, and the results are in good agreement with the experimental data. Seebeck coefficients were determined as 107 {micro}V/K and 136 {micro}V/K for samples grown at 1350 C with AsH{sub 3}/B{sub 2}H{sub 6} flow ratio equals to 1:1 and 3:5, respectively.

  9. Scanning Seebeck Coefficient Measurement System for Homogeneity Characterization of Bulk and Thin-Film Thermoelectric Materials

    SciTech Connect

    Iwanaga, S; Snyder, GJ

    2012-04-03

    Larger-scale production of thermoelectric materials is necessary when mass-producing thermoelectric devices at industrial level. Certain fabrication techniques can create inhomogeneity in the material through composition and doping fluctuations throughout the sample, causing local variations in thermoelectric properties. Some variations are in the range of sub-millimeter scale or larger but may be difficult to detect by traditional materials characterization techniques such as x-ray diffraction or scanning electron microscopy when the chemical variation is small but the doping variation, which strongly affects thermoelectric performance, is large. In this paper, a scanning apparatus to directly detect local variations of Seebeck coefficient on both bulk and thin-film samples is used. Results have shown that this technique can be utilized for detection of defective regions, as well as phase separation in the 100-m range or larger.

  10. Large Seebeck coefficients of protonated titanate nanotubes for high-temperature thermoelectric conversion.

    PubMed

    Miao, L; Tanemura, S; Huang, R; Liu, C Y; Huang, C M; Xu, G

    2010-08-01

    Titanate nanotubes Na(2-x)H(x)Ti(3)O(7) produced by alkali hydrothermally treated ground TiO(2) aerogels are investigated as possible materials for high-temperature thermoelectric conversion by measuring their thermoelectric properties. Strikingly, the Seebeck coefficients increased sharply in the temperature range 745 to 1032 K, reaching a maximum of 302 muV/K. The electrical resistivity of the TNNTs ranged from 325 to 525 Omegam, which is lower than that of bulk TiO(2), and thermal conductivities at room temperature were also very low, ranging from 0.55 to 0.75 Wm(-1) K(-1). The hollow structure of the titanate nanotubes, with small, uniform diameters, is thought to be responsible for the ultralow thermal conductivity. The large thermoelectric power and ultralow thermal conductivity suggest that titanate nanotubes represent a new kind of p-type oxide thermoelectric material. PMID:20735107

  11. Giant Seebeck coefficient thermoelectric device of MnO2 powder.

    PubMed

    Song, FangFang; Wu, Liming; Liang, S

    2012-03-01

    We report a giant Seebeck coefficient (S) thermoelectric (TE) material-MnO(2) powder-and the design of a practical MnO(2) TE generator to light up a regular light emitting diode (LED). The S of MnO(2) powder was measured to be higher than 20,000 μV K(-1), which is about 100 times higher than the state-of-the-art of Bi(2)Te(3), one of the best TE materials. The giant S is very possibly closely related to the surface density of the electronic state (DOS), the Fermi energy level. The very high S and therefore high power factor is technologically important for transient TE cooling. PMID:22293218

  12. Use of Photothermally Generated Seebeck Voltage for Thermal Characterization of Thermoelectric Materials

    NASA Astrophysics Data System (ADS)

    Kuriakose, Maju; Depriester, Michael; King, Roch Chan Yu; Roussel, Frédérick; Sahraoui, Abdelhak Hadj

    2014-06-01

    A simple and accurate experimental procedure to measure simultaneously the thermal properties (conductivity, diffusivity, and effusivity) of thermoelectric (TE) materials using their Seebeck voltage is proposed. The technique is based on analysis of a periodically oscillating thermoelectric signal generated from a TE material when it is thermally excited using an intensity-modulated laser source. A self-normalization procedure is implemented in the presented method using TE signals generated by changing the laser heating from one side to another of the TE material. Experiments are done on a polyaniline carbon nanohybrid (6.6 wt.% carbon nanotubes), yielding a thermal conductivity of 1.106 ± 0.001 W/m-K. The results are compared with the results from photothermal infrared radiometry experiments.

  13. Record Seebeck coefficient and extremely low thermal conductivity in nanostructured SnSe

    SciTech Connect

    Serrano-Sánchez, F.; Gharsallah, M.; Nemes, N. M.; Mompean, F. J.; Martínez, J. L.; Alonso, J. A.

    2015-02-23

    SnSe has been prepared by arc-melting, as mechanically robust pellets, consisting of highly oriented polycrystals. This material has been characterized by neutron powder diffraction (NPD), scanning electron microscopy, and transport measurements. A microscopic analysis from NPD data demonstrates a quite perfect stoichiometry SnSe{sub 0.98(2)} and a fair amount of anharmonicity of the chemical bonds. The Seebeck coefficient reaches a record maximum value of 668 μV K{sup −1} at 380 K; simultaneously, this highly oriented sample exhibits an extremely low thermal conductivity lower than 0.1 W m{sup −1} K{sup −1} around room temperature, which are two of the main ingredients of good thermoelectric materials. These excellent features exceed the reported values for this semiconducting compound in single crystalline form in the moderate-temperatures region and highlight its possibilities as a potential thermoelectric material.

  14. Strain effect on electronic structure and thermoelectric properties of orthorhombic SnSe: A first principles study

    SciTech Connect

    Cuong, Do Duc; Rhim, S. H. Hong, Soon Cheol; Lee, Joo-Hyong

    2015-11-15

    Strain effect on thermoelectricity of orthorhombic SnSe is studied using density function theory. The Seebeck coefficients are obtained by solving Boltzmann Transport equation (BTE) with interpolated band energies. As expected from the crystal structure, calculated Seebeck coefficients are highly anisotropic, and agree well with experiment. Changes in the Seebeck coefficients are presented, when strain is applied along b and c direction with strength from -3% to +3%, where influence by band gaps and band dispersions are significant. Moreover, for compressive strains, the sign change of Seebeck coefficients at particular direction suggests that the bipolar transport is possible for SnSe.

  15. Strain effect on electronic structure and thermoelectric properties of orthorhombic SnSe: A first principles study

    NASA Astrophysics Data System (ADS)

    Cuong, Do Duc; Rhim, S. H.; Lee, Joo-Hyong; Hong, Soon Cheol

    2015-11-01

    Strain effect on thermoelectricity of orthorhombic SnSe is studied using density function theory. The Seebeck coefficients are obtained by solving Boltzmann Transport equation (BTE) with interpolated band energies. As expected from the crystal structure, calculated Seebeck coefficients are highly anisotropic, and agree well with experiment. Changes in the Seebeck coefficients are presented, when strain is applied along b and c direction with strength from -3% to +3%, where influence by band gaps and band dispersions are significant. Moreover, for compressive strains, the sign change of Seebeck coefficients at particular direction suggests that the bipolar transport is possible for SnSe.

  16. Seebeck Coefficient Measurements on Micron-Size Single-Crystal Zinc Germanium Nitride Rods

    NASA Astrophysics Data System (ADS)

    Dyck, J. S.; Colvin, J. R.; Quayle, P. C.; Peshek, T. J.; Kash, K.

    2016-01-01

    II-IV-nitride compounds are tetrahedrally bonded, heterovalent ternary semiconductors that have recently garnered attention for their potential technological applications. These materials are derived from the parent III-nitride compounds; ZnGeN2 is the II-IV-nitride analogue to the III-nitride GaN. Very little is known about the transport properties of ZnGeN2. In this work, we present Seebeck coefficient (S) data on 3-micron-diameter, 70-micron-long, single-crystal ZnGeN2 rods, employing a novel measurement approach. The measurements of S show that the majority free carriers are electrons, and imply that the carrier gas is degenerate. Within a single-band model for the conduction band, a carrier concentration of order 1019 cm-3 was estimated for a measured S = -90 μV/K. Together with electrical transport measurements, a lower limit for the electron mobility is estimated to be ˜20 cm2/V-s. A discussion of this material as a thermoelectric is presented. The background level of free electrons in this unintentionally doped ZnGeN2 is very near the predicted optimum value for maximum thermoelectric performance.

  17. Seebeck Coefficient Measurements on Micron-Size Single-Crystal Zinc Germanium Nitride Rods

    NASA Astrophysics Data System (ADS)

    Dyck, J. S.; Colvin, J. R.; Quayle, P. C.; Peshek, T. J.; Kash, K.

    2016-06-01

    II-IV-nitride compounds are tetrahedrally bonded, heterovalent ternary semiconductors that have recently garnered attention for their potential technological applications. These materials are derived from the parent III-nitride compounds; ZnGeN2 is the II-IV-nitride analogue to the III-nitride GaN. Very little is known about the transport properties of ZnGeN2. In this work, we present Seebeck coefficient ( S) data on 3-micron-diameter, 70-micron-long, single-crystal ZnGeN2 rods, employing a novel measurement approach. The measurements of S show that the majority free carriers are electrons, and imply that the carrier gas is degenerate. Within a single-band model for the conduction band, a carrier concentration of order 1019 cm-3 was estimated for a measured S = -90 μV/K. Together with electrical transport measurements, a lower limit for the electron mobility is estimated to be ˜20 cm2/V-s. A discussion of this material as a thermoelectric is presented. The background level of free electrons in this unintentionally doped ZnGeN2 is very near the predicted optimum value for maximum thermoelectric performance.

  18. The Seebeck Coefficient in Oxygen Enriched La2NiO4

    NASA Astrophysics Data System (ADS)

    Bach, Paul; Leboran, Victor; Rivadulla, Francisco

    2013-03-01

    Oxide-based devices show promise for themoelectric applications due to their chemical stability and straightforward fabrication. The La2NiO4+δ system has been predicted to show an increased thermopower coupled with an increased electrical conductivity around δ = 0 . 05 [Pardo et al. PRB 86, 165114 (2012)] that could lead to a large thermoelectric figure of merit (ZT). We investigate the suitability of lanthanum nickelate as a candidate material for high-ZT devices through a systematic study of oxygenated thin films grown by pulsed laser deposition. We report the electrical conductivity, Seebeck coefficient, and structural morphology of La2NiO4 grown in a range of oxidizing atmospheres and discuss their implications for controlled engineering of thermoelectric properties. We have explored the possibility of gate-tuning these systems in order to fabricate single-oxide based devices. This work was supported by the Ministerio de Ciencia e Innovación (Spain), grant MAT2010-16157, and the European Research Council, grant ERC-2010-StG 259082 2D THERMS.

  19. Thermoelectric performance of poly(3-hexylthiophene) films doped by iodine vapor with promising high seebeck coefficient

    NASA Astrophysics Data System (ADS)

    Zhu, Hongfei; Liu, Congcong; Song, Haijun; Xu, Jingkun; Kong, Fangfang; Wang, Jianmin

    2014-03-01

    Poly(3-hexylthiophene) (P3HT) films doped with iodine vapor have been prepared by casting a P3HT solution on glass substrates and their thermoelectric (TE) performances has been investigated. The maximum Seebeck coefficient and electrical conductivity of iodine-doped P3HT films were 386 µV·K-1 (at room temperature) and 4.7 × 10-1 S·cm-1, which is about five orders of magnitude higher than that of pristine P3HT films. The power factor of these iodine-doped P3HT films was estimated to be 7.0 µW·m-1·K-2 at room temperature, which is a relative high value for organic TE materials. The UV-vis spectra of iodine-doped P3HT films showed a slight red shift of the iodine-doped P3HT compared to those of pristine P3HT films. Atomic force microscopy images indicated the conformational changes in P3HT chains after treatment with iodine vapor. During this treatment, the P3HT chains self-organized into a more ordered structure, this organization improved the charge carrier transport capability and the TE performance of P3HT the films.

  20. Seebeck Coefficient of Manganese Oxide Nanoparticles as a Function of Ohmic Resistance

    NASA Astrophysics Data System (ADS)

    Francis, Nicholas; Hedden, Morgan; Constantin, Costel

    2013-03-01

    Due to the ever increasing energy demand and growing global concern over the environmental impact of CO2 emissions, there is an urging need to seek solutions to transit from fossil fuels to sustainable energy. Thermoelectric (TE) materials show great promise for converting waste heat energy into electricity. TE systems have many unique advantages such as silent operationality, time reliability, and dimensional scalability. Most recently, researchers Song et al. found that MnO2 nanoparticles show a giant Seebeck coefficient of S = 20 mV/K, which is100 times higher than bismuth telluride, one of the best TE materials. Song et al. concluded the paper claiming that the giant S is related to the surface density of the electronic states (DOS). However, they provided very little information about the S as a function of Ohmic resistance [R] for different nano particle sizes which can give information about the DOS. Our preliminary results show that there is a sudden increase of S from 0.33-0.63 mV/K as R increases from 80-110 Ohms. This transition has never been seen before and it can give clues as to the existence of the Giant S observed in this material. This work was supported in part by U.S. Department of Energy Grant #DE-EE0003100..

  1. Thermal conductivity and Seebeck coefficients of icosahedral boron arsenide films on silicon carbide

    SciTech Connect

    Gong, Y.; Kuball, M.; Zhang, Y.; Dudley, M.; Zhang, Y.; Edgar, J. H.; Heard, P. J.

    2010-10-15

    The thermal conductivity of icosahedral boron arsenide (B{sub 12}As{sub 2}) films grown on (0001) 6H-SiC substrates by chemical vapor deposition was studied by the 3{omega} technique. The room temperature thermal conductivity decreased from 27.0 to 15.3 W/m K as the growth temperature was decreased from 1450 to 1275 deg. C. This is mainly attributed to the differences in the impurity concentration and microstructure, determined from secondary ion mass spectrometry and high resolution transmission electron microscopy, respectively. Callaway's theory was applied to calculate the temperature-dependent thermal conductivity, and the results are in good agreement with the experimental data. Seebeck coefficients were determined as 107 {mu}V/K and 136 {mu}V/K for samples grown at 1350 deg. C with AsH{sub 3}/B{sub 2}H{sub 6} flow ratio equals to 1:1 and 3:5, respectively.

  2. Thermoelectricity at the molecular scale: a large Seebeck effect in endohedral metallofullerenes

    NASA Astrophysics Data System (ADS)

    Lee, See Kei; Buerkle, Marius; Yamada, Ryo; Asai, Yoshihiro; Tada, Hirokazu

    2015-12-01

    Single molecule devices provide a unique system to study the thermoelectric energy conversion at an atomistic level and can provide valuable information for the design of organic thermoelectric materials. Here we present a comprehensive study of the thermoelectric transport properties of molecular junctions based on C82, Gd@C82, and Ce@C82. We combine precise scanning tunneling microscope break-junction measurements of the thermopower and conductance with quantitatively accurate self-energy-corrected first-principles transport calculations. We find that all three fullerene derivatives give rise to a negative thermopower (n-conducting). The absolute value, however, is much larger for the Gd@C82 and Ce@C82 junctions. The conductance, on the other hand, remains comparable for all three systems. The power factor determined for the Gd@C82 based junction is so far the highest obtained for a single-molecule device. Although the encapsulated metal atom does not directly contribute to the transport, we show that the observed enhancement of the thermopower for Gd@C82 and Ce@C82 is elucidated by the substantial changes in the electronic- and geometrical structure of the fullerene molecule induced by the encapsulated metal atom.Single molecule devices provide a unique system to study the thermoelectric energy conversion at an atomistic level and can provide valuable information for the design of organic thermoelectric materials. Here we present a comprehensive study of the thermoelectric transport properties of molecular junctions based on C82, Gd@C82, and Ce@C82. We combine precise scanning tunneling microscope break-junction measurements of the thermopower and conductance with quantitatively accurate self-energy-corrected first-principles transport calculations. We find that all three fullerene derivatives give rise to a negative thermopower (n-conducting). The absolute value, however, is much larger for the Gd@C82 and Ce@C82 junctions. The conductance, on the other hand, remains comparable for all three systems. The power factor determined for the Gd@C82 based junction is so far the highest obtained for a single-molecule device. Although the encapsulated metal atom does not directly contribute to the transport, we show that the observed enhancement of the thermopower for Gd@C82 and Ce@C82 is elucidated by the substantial changes in the electronic- and geometrical structure of the fullerene molecule induced by the encapsulated metal atom. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr05394c

  3. Thermoelectricity at the molecular scale: a large Seebeck effect in endohedral metallofullerenes.

    PubMed

    Lee, See Kei; Buerkle, Marius; Yamada, Ryo; Asai, Yoshihiro; Tada, Hirokazu

    2015-12-28

    Single molecule devices provide a unique system to study the thermoelectric energy conversion at an atomistic level and can provide valuable information for the design of organic thermoelectric materials. Here we present a comprehensive study of the thermoelectric transport properties of molecular junctions based on C(82), Gd@C(82), and Ce@C(82). We combine precise scanning tunneling microscope break-junction measurements of the thermopower and conductance with quantitatively accurate self-energy-corrected first-principles transport calculations. We find that all three fullerene derivatives give rise to a negative thermopower (n-conducting). The absolute value, however, is much larger for the Gd@C(82) and Ce@C(82) junctions. The conductance, on the other hand, remains comparable for all three systems. The power factor determined for the Gd@C(82) based junction is so far the highest obtained for a single-molecule device. Although the encapsulated metal atom does not directly contribute to the transport, we show that the observed enhancement of the thermopower for Gd@C(82) and Ce@C(82) is elucidated by the substantial changes in the electronic- and geometrical structure of the fullerene molecule induced by the encapsulated metal atom. PMID:26583505

  4. Spin-dependent Seebeck effects in graphene-based molecular junctions

    NASA Astrophysics Data System (ADS)

    Li, Jianwei; Wang, Bin; Xu, Fuming; Wei, Yadong; Wang, Jian

    2016-05-01

    We report a first-principles investigation of spin-dependent transport properties in two different graphene-based molecular junctions. By applying different temperatures between two leads without bias voltage, spin-dependent currents are driven which depend on reference temperature T , temperature gradient Δ T , and gate voltage Vg. Moreover, pure spin currents without charge currents can be obtained by adjusting T ,Δ T , and Vg for both molecular junctions. The directions of pure spin currents in these two molecular junctions are opposite, which can be understood by analyzing the transmission coefficients under equilibrium states. Spin thermopower, thermal conductance, and the figure of merit as functions of T ,Vg, and chemical potential μ were also investigated in the linear response regime. Large spin thermopower and spin figure of merit can be obtained by adjusting Vg and μ for each junction, which indicates proper application of spin caloritronic devices of our graphene-based molecular junctions.

  5. Spin Seebeck Effect and Thermal Colossal Magnetoresistance in Graphene Nanoribbon Heterojunction

    PubMed Central

    Ni, Yun; Yao, Kailun; Fu, Huahua; Gao, Guoying; Zhu, Sicong; Wang, Shuling

    2013-01-01

    Spin caloritronics devices are very important for future development of low-power-consumption technology. We propose a new spin caloritronics device based on zigzag graphene nanoribbon (ZGNR), which is a heterojunction consisting of single-hydrogen-terminated ZGNR (ZGNR-H) and double-hydrogen-terminated ZGNR (ZGNR-H2). We predict that spin-up and spin-down currents flowing in opposite directions can be induced by temperature difference instead of external electrical bias. The thermal spin-up current is considerably large and greatly improved compared with previous work in graphene. Moreover, the thermal colossal magnetoresistance is obtained in our research, which could be used to fabricate highly-efficient spin caloritronics MR devices. PMID:23459307

  6. Determination of spin-dependent Seebeck coefficients of CoFeB/MgO/CoFeB magnetic tunnel junction nanopillars

    NASA Astrophysics Data System (ADS)

    Liebing, N.; Serrano-Guisan, S.; Rott, K.; Reiss, G.; Langer, J.; Ocker, B.; Schumacher, H. W.

    2012-04-01

    We investigate the spin-dependent Seebeck coefficient and the tunneling magneto thermopower (TMTP) of CoFeB/MgO/CoFeB magnetic tunnel junctions (MTJ) in the presence of thermal gradients across the MTJ. The thermo power voltage VTP across the MTJ is found to scale linearly with the heating power and reveals similar field dependence as the tunnel magnetoresistance (TMR). Based on calibration measurements and finite element simulations of the heat flux, the thermal gradient and large spin-dependent Seebeck coefficients of the order of (240 ± 110) μV/K are derived. From additional measurements on MTJs after dielectric breakdown, a TMR up to 90% and Seebeck coefficients up to 650 μV/K can be derived.

  7. Nernst and Seebeck coefficients of the cuprate superconductor YBa2Cu3O6.67: a study of Fermi surface reconstruction.

    PubMed

    Chang, J; Daou, R; Proust, Cyril; Leboeuf, David; Doiron-Leyraud, Nicolas; Laliberté, Francis; Pingault, B; Ramshaw, B J; Liang, Ruixing; Bonn, D A; Hardy, W N; Takagi, H; Antunes, A B; Sheikin, I; Behnia, K; Taillefer, Louis

    2010-02-01

    The Seebeck and Nernst coefficients S and nu of the cuprate superconductor YBa{2}Cu{3}O{y} (YBCO) were measured in a single crystal with doping p=0.12 in magnetic fields up to H=28 T. Down to T=9 K, nu becomes independent of field by H approximately 30 T, showing that superconducting fluctuations have become negligible. In this field-induced normal state, S/T and nu/T are both large and negative in the T-->0 limit, with the magnitude and sign of S/T consistent with the small electronlike Fermi surface pocket detected previously by quantum oscillations and the Hall effect. The change of sign in S(T) at T approximately 50 K is remarkably similar to that observed in La2-xBaxCuO4, La{2-x-y}Nd{y}Sr_{x}CuO{4}, and La{2-x-y}Eu{y}Sr{x}CuO{4}, where it is clearly associated with the onset of stripe order. We propose that a similar density-wave mechanism causes the Fermi surface reconstruction in YBCO. PMID:20366789

  8. Band gap estimation from temperature dependent Seebeck measurement—Deviations from the 2e|S|{sub max}T{sub max} relation

    SciTech Connect

    Gibbs, Zachary M.; Kim, Hyun-Sik; Wang, Heng; Snyder, G. Jeffrey

    2015-01-12

    In characterizing thermoelectric materials, electrical and thermal transport measurements are often used to estimate electronic band structure properties such as the effective mass and band gap. The Goldsmid-Sharp band gap, E{sub g} = 2e|S|{sub max}T{sub max}, is a tool widely employed to estimate the band gap from temperature dependent Seebeck coefficient measurements. However, significant deviations of more than a factor of two are now known to occur. We find that this is when either the majority-to-minority weighted mobility ratio (A) becomes very different from 1.0 or as the band gap (E{sub g}) becomes significantly smaller than 10 k{sub B}T. For narrow gaps (E{sub g} ≲ 6 k{sub B}T), the Maxwell-Boltzmann statistics applied by Goldsmid-Sharp break down and Fermi-Dirac statistics are required. We generate a chart that can be used to quickly estimate the expected correction to the Goldsmid-Sharp band gap depending on A and S{sub max}; however, additional errors can occur for S < 150 μV/K due to degenerate behavior.

  9. High temperature setup for measurements of Seebeck coefficient and electrical resistivity of thin films using inductive heating.

    PubMed

    Adnane, L; Williams, N; Silva, H; Gokirmak, A

    2015-10-01

    We have developed an automated setup for simultaneous measurement of Seebeck coefficient S(T) and electrical resistivity ρ(T) of thin film samples from room temperature to ∼650 °C. S and ρ are extracted from current-voltage (I-V) measurements obtained using a semiconductor parameter analyzer and temperature measurements obtained using commercial thermocouples. The slope and the x-axis intercept of the I-V characteristics represent the sample conductance G and the Seebeck voltage, respectively. The measured G(T) can be scaled to ρ(T) by the geometry factor obtained from the room temperature resistivity measurement of the film. The setup uses resistive or inductive heating to control the temperature and temperature gradient on the sample. Inductive heating is achieved with steel plates that surround the test area and a water cooled copper pipe coil underneath that generates an AC magnetic field. The measurements can be performed using resistive heating only or inductive heating only, or a combination of both depending on the desired heating ranges. Inductive heating provides a more uniform heating of the test area, does not require contacts to the sample holder, can be used up to the Curie temperature of the particular magnetic material, and the temperature gradients can be adjusted by the relative positions of the coil and sample. Example results obtained for low doped single-crystal silicon with inductive heating only and with resistive heating only are presented. PMID:26520996

  10. Statistical Analysis of a Round-Robin Measurement Survey of Two Candidate Materials for a Seebeck Coefficient Standard Reference Material

    PubMed Central

    Lu, Z. Q. J.; Lowhorn, N. D.; Wong-Ng, W.; Zhang, W.; Thomas, E. L.; Otani, M.; Green, M. L.; Tran, T. N.; Caylor, C.; Dilley, N. R.; Downey, A.; Edwards, B.; Elsner, N.; Ghamaty, S.; Hogan, T.; Jie, Q.; Li, Q.; Martin, J.; Nolas, G.; Obara, H.; Sharp, J.; Venkatasubramanian, R.; Willigan, R.; Yang, J.; Tritt, T.

    2009-01-01

    In an effort to develop a Standard Reference Material (SRM™) for Seebeck coefficient, we have conducted a round-robin measurement survey of two candidate materials—undoped Bi2Te3 and Constantan (55 % Cu and 45 % Ni alloy). Measurements were performed in two rounds by twelve laboratories involved in active thermoelectric research using a number of different commercial and custom-built measurement systems and techniques. In this paper we report the detailed statistical analyses on the interlaboratory measurement results and the statistical methodology for analysis of irregularly sampled measurement curves in the interlaboratory study setting. Based on these results, we have selected Bi2Te3 as the prototype standard material. Once available, this SRM will be useful for future interlaboratory data comparison and instrument calibrations.

  11. Seebeck and figure of merit enhancement in nanostructured antimony telluride by antisite defect suppression through sulfur doping.

    PubMed

    Mehta, Rutvik J; Zhang, Yanliang; Zhu, Hong; Parker, David S; Belley, Matthew; Singh, David J; Ramprasad, Ramamurthy; Borca-Tasciuc, Theodorian; Ramanath, Ganpati

    2012-09-12

    Antimony telluride has a low thermoelectric figure of merit (ZT < ∼0.3) because of a low Seebeck coefficient α arising from high degenerate hole concentrations generated by antimony antisite defects. Here, we mitigate this key problem by suppressing antisite defect formation using subatomic percent sulfur doping. The resultant 10-25% higher α in bulk nanocrystalline antimony telluride leads to ZT ∼ 0.95 at 423 K, which is superior to the best non-nanostructured antimony telluride alloys. Density functional theory calculations indicate that sulfur increases the antisite formation activation energy and presage further improvements leading to ZT ∼ 2 through optimized doping. Our findings are promising for designing novel thermoelectric materials for refrigeration, waste heat recovery, and solar thermal applications. PMID:22891784

  12. Thermoelectric properties of the unfilled skutterudite FeSb3 from first-principles and Seebeck local probes

    SciTech Connect

    Lemal, Sébastien; Nguyen, Ngoc; De Boor, Johannes; Ghosez, Philippe; Varignon, Julien; Klobes, B.; Hermann, Raphael P; Verstraete, Matthieu

    2015-01-01

    Using a combination of first-principles calculations and experimental transport measurements, we study the electronic and magnetic structure of the unfilled skutterudite FeSb3. We employ the hybrid functional approach for exchange-correlation. The ground state is determined to be anti-ferromagnetic with an atomic magnetic moment of 1.6 B/Fe. The N eel temperature TN is estimated at 6 K, in agreement with experiments which found a paramagnetic state down to 10 K. The ground state is semiconducting, with a small electronic gap of 33 meV, also consistent with previous experiments on films. Charge carrier concentrations are estimated from Hall resistance measurements. The Seebeck coefficient is measured and mapped using a scanning probe at room temperature that yields an average value of 38.6 VK 1, slightly lower than the theoretical result. The theoretical conductivity is analyzed as a function of temperature and concentration of charge carriers.

  13. Reliable measurement of the Seebeck coefficient of organic and inorganic materials between 260 K and 460 K

    SciTech Connect

    Beretta, D.; Lanzani, G.; Bruno, P.; Caironi, M.

    2015-07-15

    A new experimental setup for reliable measurement of the in-plane Seebeck coefficient of organic and inorganic thin films and bulk materials is reported. The system is based on the “Quasi-Static” approach and can measure the thermopower in the range of temperature between 260 K and 460 K. The system has been tested on a pure nickel bulk sample and on a thin film of commercially available PEDOT:PSS deposited by spin coating on glass. Repeatability within 1.5% for the nickel sample is demonstrated, while accuracy in the measurement of both organic and inorganic samples is guaranteed by time interpolation of data and by operating with a temperature difference over the sample of less than 1 K.

  14. Effets Seebeck et Nernst dans les cuprates: Etude de la reconstruction de la surface de Fermi sous champ magnetique intense

    NASA Astrophysics Data System (ADS)

    Laliberte, Francis

    2010-06-01

    Ce memoire presente des mesures de transport thermoelectrique, les effets Seebeck et Nernst, dans une serie d'echantillons de supraconducteurs a haute temperature critique. Des resultats obtenus recemment au Laboratoire National des Champs Magnetiques Intenses a Grenoble sur La1.7Eu0.2Sr0.1 CuO4, La1.675Eu0.2Sr0.125CuO 4, La1.64Eu0.2Sr0.16CuO4, La1.74Eu0.1Sr0.16CuO4 et La 1.4Nd0.4Sr0.2CuO4 sont analyses. Une attention particuliere est accordee aux equations de la theorie semi-classique du transport et leur validite est verifiee. La procedure experimentale et les materiaux utilises pour concevoir les montages de mesures sont expliques en detail. Enfin, un chapitre est dedie a l'explication et l'interpretation des resultats de transport thermoelectrique sur YBa2Cu3O6+delta publies au cours de l'hiver 2010 dans les revues Nature et Physical Review Letters. Les donnees d'effet Seebeck dans les echantillons de La 1.8-x,Eu0.2SrxCuO 4, ou un changement de signe est observe, permettent de conclure a la presence d'une poche d'electrons dans la surface de Fermi qui domine le transport a basse temperature dans la region sous-dopee du diagramme de phase. Cette conclusion est similaire a celle obtenue par des mesures d'effet Hall dans YBa 2Cu3O6+delta et elle cadre bien dans un scenario de reconstruction de la surface de Fermi. Les donnees d'effet Nernst recueillies indiquent que la contribution des fluctuations supraconductrices est limitee a un modeste intervalle de temperature au-dessus de la temperature critique.

  15. Observations of Co4+ in a Higher Spin State and the Increase in the Seebeck Coefficient of Thermoelectric Ca3Co4O9

    SciTech Connect

    Klie, Robert F; Qiao, Q.; Paulauskas, T.; Gulec, A.; Rebola, A.; Ogut, Serdar; Prange, Micah P; Idrobo Tapia, Juan C; Pantelides, Sokrates T.; Kolesnik, S.; Dabrowski, B.; Ozdemir, M.; Boyraz, C.; Mazumdar, Dipanjan; Gupta, Dr. Arunava

    2012-01-01

    Ca{sub 3}Co{sub 4}O{sub 9} has a unique structure that leads to exceptionally high thermoelectric transport. Here we report the achievement of a 27% increase in the room-temperature in-plane Seebeck coefficient of Ca{sub 3}Co{sub 4}O{sub 9} thin films. We combine aberration-corrected Z-contrast imaging, atomic-column resolved electron energy-loss spectroscopy, and density-functional calculations to show that the increase is caused by stacking faults with Co4+-ions in a higher spin state compared to that of bulk Ca{sub 3}Co{sub 4}O{sub 9}. The higher Seebeck coefficient makes the Ca{sub 3}Co{sub 4}O{sub 9} system suitable for many high temperature waste-heat-recovery applications.

  16. Hall and Seebeck measurements estimate the thickness of a (buried) carrier system: Identifying interface electrons in In-doped SnO{sub 2} films

    SciTech Connect

    Papadogianni, Alexandra; Bierwagen, Oliver; White, Mark E.; Speck, James S.; Galazka, Zbigniew

    2015-12-21

    We propose a simple method based on the combination of Hall and Seebeck measurements to estimate the thickness of a carrier system within a semiconductor film. As an example, this method can distinguish “bulk” carriers, with homogeneous depth distribution, from “sheet” carriers, that are accumulated within a thin layer. The thickness of the carrier system is calculated as the ratio of the integral sheet carrier concentration, extracted from Hall measurements, to the volume carrier concentration, derived from the measured Seebeck coefficient of the same sample. For rutile SnO{sub 2}, the necessary relation of Seebeck coefficient to volume electron concentration in the range of 3 × 10{sup 17} to 3 × 10{sup 20 }cm{sup −3} has been experimentally obtained from a set of single crystalline thin films doped with varying Sb-doping concentrations and unintentionally doped bulk samples, and is given as a “calibration curve.” Using this calibration curve, our method demonstrates the presence of interface electrons in homogeneously deep-acceptor (In) doped SnO{sub 2} films on sapphire substrates.

  17. Thermoelectric properties of the unfilled skutterudite FeSb3 from first principles and Seebeck local probes

    SciTech Connect

    Lemal, Sébastien; Nguyen, Ngoc; de Boor, Johannes; Ghosez, Philippe; Varignon, Julien; Klobes, Benedikt; Hermann, Raphaël P.; Verstraete, Matthieu J.

    2015-11-16

    In this paper, using a combination of first-principles calculations and experimental transport measurements, we study the electronic and magnetic structure of the unfilled skutterudite FeSb3. We employ the hybrid functional approach for exchange correlation. The ground state is determined to be antiferromagnetic with an atomic magnetic moment of 1.6μB/Fe. The Néel temperature TN is estimated at 6 K, in agreement with experiments which found a paramagnetic state down to 10 K. The ground state is semiconducting, with a small electronic gap of 33meV, also consistent with previous experiments on films. Charge carrier concentrations are estimated from Hall resistance measurements. The Seebeck coefficient is measured and mapped using a scanning probe at room temperature that yields an average value of 38.6μVK-1, slightly lower than the theoretical result. Finally, the theoretical conductivity is analyzed as a function of temperature and concentration of charge carriers.

  18. Giant thermoelectric Seebeck coefficient of a two-dimensional electron gas in SrTiO3.

    PubMed

    Ohta, Hiromichi; Kim, Sungwng; Mune, Yoriko; Mizoguchi, Teruyasu; Nomura, Kenji; Ohta, Shingo; Nomura, Takashi; Nakanishi, Yuki; Ikuhara, Yuichi; Hirano, Masahiro; Hosono, Hideo; Koumoto, Kunihito

    2007-02-01

    Enhancement of the Seebeck coefficient (S ) without reducing the electrical conductivity (sigma) is essential to realize practical thermoelectric materials exhibiting a dimensionless figure of merit (ZT=S2 x sigma x T x kappa-1) exceeding 2, where T is the absolute temperature and kappa is the thermal conductivity. Here, we demonstrate that a high-density two-dimensional electron gas (2DEG) confined within a unit cell layer thickness in SrTiO(3) yields unusually large |S|, approximately five times larger than that of SrTiO(3) bulks, while maintaining a high sigma2DEG. In the best case, we observe |S|=850 microV K-1 and sigma2DEG=1.4 x 10(3) S cm-1. In addition, by using the kappa of bulk single-crystal SrTiO(3) at room temperature, we estimate ZT approximately 2.4 for the 2DEG, corresponding to ZT approximately 0.24 for a complete device having the 2DEG as the active region. The present approach using a 2DEG provides a new route to realize practical thermoelectric materials without the use of toxic heavy elements. PMID:17237790

  19. Transport Properties of Bulk Thermoelectrics An International Round-Robin Study, Part I: Seebeck Coefficient and Electrical Resistivity

    SciTech Connect

    Wang, Hsin; Porter, Wallace D; Bottner, Harold; Konig, Jan; Chen, Lidong; Bai, Shengqiang; Tritt, Terry M.; Mayolett, Alex; Senawiratne, Jayantha; Smith, Charlene; Harris, Fred; Gilbert, Partricia; Sharp, Jeff; Lo, Jason; Keinke, Holger; Kiss, Laszlo I.

    2013-01-01

    Recent research and development of high temperature thermoelectric materials has demonstrated great potential of converting automobile exhaust heat directly into electricity. Thermoelectrics based on classic bismuth telluride have also started to impact the automotive industry by enhancing air conditioning efficiency and integrated cabin climate control. In addition to engineering challenges of making reliable and efficient devices to withstand thermal and mechanical cycling, the remaining issues in thermoelectric power generation and refrigeration are mostly materials related. The figure-of-merit, ZT, still needs to improve from the current value of 1.0 - 1.5 to above 2 to be competitive to other alternative technologies. In the meantime, the thermoelectric community could greatly benefit from the development of international test standards, improved test methods and better characterization tools. Internationally, thermoelectrics have been recognized by many countries as an important area for improving energy efficiency. The International Energy Agency (IEA) group under the implementing agreement for Advanced Materials for Transportation (AMT) identified thermoelectric materials as an important area in 2009. This paper is Part I of the international round-robin testing of transport properties of bulk thermoelectrics. The main focuses in Part I are on two electronic transport properties: Seebeck coefficient and electrical resistivity.

  20. Thermoelectric properties of the unfilled skutterudite FeSb3 from first principles and Seebeck local probes

    DOE PAGESBeta

    Lemal, Sébastien; Nguyen, Ngoc; de Boor, Johannes; Ghosez, Philippe; Varignon, Julien; Klobes, Benedikt; Hermann, Raphaël P.; Verstraete, Matthieu J.

    2015-11-16

    In this paper, using a combination of first-principles calculations and experimental transport measurements, we study the electronic and magnetic structure of the unfilled skutterudite FeSb3. We employ the hybrid functional approach for exchange correlation. The ground state is determined to be antiferromagnetic with an atomic magnetic moment of 1.6μB/Fe. The Néel temperature TN is estimated at 6 K, in agreement with experiments which found a paramagnetic state down to 10 K. The ground state is semiconducting, with a small electronic gap of 33meV, also consistent with previous experiments on films. Charge carrier concentrations are estimated from Hall resistance measurements. Themore » Seebeck coefficient is measured and mapped using a scanning probe at room temperature that yields an average value of 38.6μVK-1, slightly lower than the theoretical result. Finally, the theoretical conductivity is analyzed as a function of temperature and concentration of charge carriers.« less

  1. Transport Properties of Bulk Thermoelectrics—An International Round-Robin Study, Part I: Seebeck Coefficient and Electrical Resistivity

    NASA Astrophysics Data System (ADS)

    Wang, Hsin; Porter, Wallace D.; Böttner, Harald; König, Jan; Chen, Lidong; Bai, Shengqiang; Tritt, Terry M.; Mayolet, Alex; Senawiratne, Jayantha; Smith, Charlene; Harris, Fred; Gilbert, Patricia; Sharp, Jeff W.; Lo, Jason; Kleinke, Holger; Kiss, Laszlo

    2013-04-01

    Recent research and development of high-temperature thermoelectric materials has demonstrated great potential for converting automobile exhaust heat directly into electricity. Thermoelectrics based on classic bismuth telluride have also started to impact the automotive industry by enhancing air-conditioning efficiency and integrated cabin climate control. In addition to engineering challenges of making reliable and efficient devices to withstand thermal and mechanical cycling, the remaining issues in thermoelectric power generation and refrigeration are mostly materials related. The dimensionless figure of merit, ZT, still needs to be improved from the current value of 1.0 to 1.5 to above 2.0 to be competitive with other alternative technologies. In the meantime, the thermoelectric community could greatly benefit from the development of international test standards, improved test methods, and better characterization tools. Internationally, thermoelectrics have been recognized by many countries as a key component for improving energy efficiency. The International Energy Agency (IEA) group under the Implementing Agreement for Advanced Materials for Transportation (AMT) identified thermoelectric materials as an important area in 2009. This paper is part I of the international round-robin testing of transport properties of bulk thermoelectrics. The main foci in part I are the measurement of two electronic transport properties: Seebeck coefficient and electrical resistivity.

  2. Thin film thermoelectric metal-organic framework with high Seebeck coefficient and low thermal conductivity (Presentation Recording)

    NASA Astrophysics Data System (ADS)

    Erickson, Kristopher J.; Leonard, Francois; Stavila, Vitalie N.; Foster, Michael E.; Spataru, Catalin D.; Jones, Reese; Foley, Brian; Hopkins, Patrick; Allendorf, Mark D.; Talin, A. Alec

    2015-08-01

    Inorganic, low bandgap semiconductors such as Bi2Te3 have adequate efficiency for some thermoelectric energy conversion applications, but have not been more widely adopted because they are difficult to deposit over complex and/or high surface area structures, are not eco-friendly, and are too expensive. As an alternative, conducting polymers have recently attracted much attention for thermoelectric applications motivated by their low material cost, ease of processability, non-toxicity, and low thermal conductivity. Metal-organic frameworks (MOFs), which are extended, crystalline compounds consisting of metal ions interconnected by organic ligands, share many of the advantages of all-organic polymers including solution processability and low thermal conductivity. Additionally, MOFs and Guest@MOF materials offer higher thermal stability (up to ~300 °C in some cases) and have long-range crystalline order which should improve charge mobility. A potential advantage of MOFs and Guest@MOF materials over all-organic polymers is the opportunity for tuning the electronic structure through appropriate choice of metal and ligand, which could solve the long-standing challenge of finding stable, high ZT n-type organic semiconductors. In our presentation, we report on thermoelectric measurements of electrically conducting TCNQ@Cu3(BTC)2 thin films deposited using a room-temperature, solution-based method, which reveal a large, positive Seebeck coefficient. Furthermore, we use time-dependent thermoreflectance (TDTR) to measure the thermal conductivity of the films, which is found to have a low value due to the presence of disorder, as suggested by molecular dynamics simulations. In addition to establishing the thermoelectric figure of merit, the thermoelectric measurements reveal for the first time that holes are the majority carriers in TCNQ@Cu3(BTC)2.

  3. Colossal enhancement of the Seebeck coefficient in FeSb2 driven by nearly ballistic phonons

    NASA Astrophysics Data System (ADS)

    Takahashi, Hidefumi; Okazaki, Ryuji; Taniguchi, Hiroki; Terasaki, Ichiro

    2015-03-01

    An unusually large S of - 45 mV/K (at 10 K) was discovered in FeSb2 single crystal, which prompted extensive investigations into its physical origin [A. Bentien et al ., EPL 80, 17008 (2007).] This compound has a small energy gap Δ ~ 5 meV, which may be caused by strong correlations of Fe 3d-electrons, as observed with Kondo insulators, and the colossally large S may be attributed to this unique band structure near the Fermi energy. However, the exceptional value of S has not been clearly explained by electron correlations, suggesting an additional contribution such as the non-equilibrium phonon-drag effect [H. Takahashi et al ., JPSJ 80, 054708 (2011)., H. Takahashi et al ., PRB 84, 205215 (2011)., and H. Takahashi et al ., PRB 88, 165205 (2013).]. Here, we report on the direct investigation of this effect by measuring the transport properties of three samples with cross sections ranging from 250 × 245 μm2 to 80 × 160 μm2. S and κ show a significant size effect, indicating that nearly ballistic phonons, which have a long mean free path relative to the sample dimensions, are responsible for the colossal S.

  4. Size effects on thermoelectric behavior of ultrathin Na{sub x}CoO{sub 2} films

    SciTech Connect

    Brinks, Peter; Rijnders, Guus; Huijben, Mark

    2014-11-10

    Size effects in thermoelectric Na{sub x}CoO{sub 2} thin films are studied, focusing on the electrical resisitivity and Seebeck coefficient. For very thin films below 10 nm, we have observed an increase in resistivity, which is in agreement with theoretical models. In contrast to a predicted simultaneous suppression of the Seebeck coefficient for ultrathin films, we observe a constant Seebeck coefficient as a function of layer thickness due to changes in the structural properties as well as the presence of strong electron correlations. This preserved high Seebeck coefficient opens up new directions for Na{sub x}CoO{sub 2} ultrathin films as basic building blocks in thermoelectric superlattices with enhanced phonon scattering.

  5. Apparatus for the measurement of electrical resistivity, Seebeck coefficient, and thermal conductivity of thermoelectric materials between 300 K and 12 K.

    PubMed

    Martin, Joshua; Nolas, George S

    2016-01-01

    We have developed a custom apparatus for the consecutive measurement of the electrical resistivity, the Seebeck coefficient, and the thermal conductivity of materials between 300 K and 12 K. These three transport properties provide for a basic understanding of the thermal and electrical properties of materials. They are of fundamental importance in identifying and optimizing new materials for thermoelectric applications. Thermoelectric applications include waste heat recovery for automobile engines and industrial power generators, solid-state refrigeration, and remote power generation for sensors and space probes. The electrical resistivity is measured using a four-probe bipolar technique, the Seebeck coefficient is measured using the quasi-steady-state condition of the differential method in a 2-probe arrangement, and the thermal conductivity is measured using a longitudinal, multiple gradient steady-state technique. We describe the instrumentation and the measurement uncertainty associated with each transport property, each of which is presented with representative measurement comparisons using round robin samples and/or certified reference materials. Transport properties data from this apparatus have supported the identification, development, and phenomenological understanding of novel thermoelectric materials. PMID:26827351

  6. Towards the Application of Structure-Property Relationship Modeling in Materials Science: Predicting the Seebeck Coefficient for Ionic Liquid/Redox Couple Systems.

    PubMed

    Sosnowska, Anita; Barycki, Maciej; Gajewicz, Agnieszka; Bobrowski, Maciej; Freza, Sylwia; Skurski, Piotr; Uhl, Stefanie; Laux, Edith; Journot, Tony; Jeandupeux, Laure; Keppner, Herbert; Puzyn, Tomasz

    2016-06-01

    This work focuses on determining the influence of both ionic-liquid (IL) type and redox couple concentration on Seebeck coefficient values of such a system. The quantitative structure-property relationship (QSPR) and read-across techniques are proposed as methods to identify structural features of ILs (mixed with LiI/I2 redox couple), which have the most influence on the Seebeck coefficient (Se ) values of the system. ILs consisting of small, symmetric cations and anions with high values of vertical electron binding energy are recognized as those with the highest values of Se . In addition, the QSPR model enables the values of Se to be predicted for each IL that belongs to the applicability domain of the model. The influence of the redox-couple concentration on values of Se is also quantitatively described. Thus, it is possible to calculate how the value of Se will change with changing redox-couple concentration. The presence of the LiI/I2 redox couple in lower concentrations increases the values of Se , as expected. PMID:26919483

  7. Apparatus for the measurement of electrical resistivity, Seebeck coefficient, and thermal conductivity of thermoelectric materials between 300 K and 12 K

    NASA Astrophysics Data System (ADS)

    Martin, Joshua; Nolas, George S.

    2016-01-01

    We have developed a custom apparatus for the consecutive measurement of the electrical resistivity, the Seebeck coefficient, and the thermal conductivity of materials between 300 K and 12 K. These three transport properties provide for a basic understanding of the thermal and electrical properties of materials. They are of fundamental importance in identifying and optimizing new materials for thermoelectric applications. Thermoelectric applications include waste heat recovery for automobile engines and industrial power generators, solid-state refrigeration, and remote power generation for sensors and space probes. The electrical resistivity is measured using a four-probe bipolar technique, the Seebeck coefficient is measured using the quasi-steady-state condition of the differential method in a 2-probe arrangement, and the thermal conductivity is measured using a longitudinal, multiple gradient steady-state technique. We describe the instrumentation and the measurement uncertainty associated with each transport property, each of which is presented with representative measurement comparisons using round robin samples and/or certified reference materials. Transport properties data from this apparatus have supported the identification, development, and phenomenological understanding of novel thermoelectric materials.

  8. Control of thermal gradient using thermoelectric coolers for study of thermal effects

    NASA Astrophysics Data System (ADS)

    Zhang, J.; Gifford, J. A.; Zhao, G. J.; Kim, D. R.; Snider, C. N.; Vargas, N.; Chen, T. Y.

    2015-05-01

    Thermoelectric coolers based on the Peltier effect have been utilized to control temperature gradient to study thermal effects in both bulk and thin film samples. The temperature gradient is controlled by two coolers and the polarity of the thermal gradient can be reversed by reversing an electric driven voltage. With appropriate controlled thermal gradient using this technique, the Nernst and the Seebeck effects can be measured in both bulk and thin film samples free of spurious contributions. In an arbitrary direction of thermal gradient, the Seebeck and the Nernst components can be decomposed from the measured signal based on the symmetry of the effects in a magnetic field.

  9. Multi-band analysis of temperature-dependent transport coefficients (conductivity, Hall, Seebeck, and Nernst) of Ni-doped CoSb3

    NASA Astrophysics Data System (ADS)

    Kajikawa, Y.

    2016-02-01

    The experimental data on the temperature dependence of the four transport coefficients, i.e., the electrical conductivity (σ), Hall coefficient (RH), Seebeck coefficient (S), and Nernst coefficient (Q), of n-type Co0.999Ni0.001Sb3 reported by Sun et al. [Nat. Commun. 6, 7475 (2015)] have been analyzed in a multi-band model, especially focusing on the low temperature data. The multi-band model includes not only the lowest valley of the conduction band at the Γ point but also satellite valleys at the second minima together with an impurity band. The lowest valley at the Γ point is assumed to split into the c1 band and the spin-orbit split-off (so) band. For the analysis, the general expression of the Nernst coefficient in the multi-band model is derived. At such low temperatures that the other bands than the c1 and the impurity band can be neglected, this expression is shown to be approximated as the sum of three terms: the intrinsic terms due to the Nernst coefficients in the two bands themselves and a cross term proportional to the difference of Seebeck coefficients between the two bands. As a result of the analysis, it is proved that the anomalous positive peak of S(T) observed around T = 20 K as well as the sharp rise of the Hall mobility observed from 15 K to 40 K are due to the transition from hopping conduction in the impurity band to conduction in the c1 band. On the other hand, the pronounced peak of Q(T) observed slightly below 40 K is proved to be due to the cross term between the impurity band and the c1 band. In addition, a shoulder of Q(T) appeared around T = 80 K lends clear evidence of the existence of the so band, while the increase in both of σ(T) and | S ( T ) | above 150 K suggests the existence of the satellite valleys.

  10. Topological Insulator and Thermoelectric Effects

    NASA Astrophysics Data System (ADS)

    Xu, Yong

    The recent discovery of topological insulator (TI) offers new opportunities for the development of thermoelectricity, because many TIs (like Bi2Te3) are excellent thermoelectric materials. In this talk, I will first introduce our theoretical predictions of anomalous Seebeck effect and strong size effect in TI [PRL 112, 226801 (2014)]. Then I will report our recent proof experiments, which find in TI thin films that (i) the hole-type Seebeck effect and the electron-type Hall effect coexist in the same TI sample for all the measured temperatures (up to 300 K), and (ii) the thermoelectric properties depend sensitively on the film thickness. The unconventional phenomena are revealed to be closely related to the topological nature of the material. These findings may inspire new ideas for designing TI-based high-efficiency thermoelectric devices.

  11. Proton irradiation effects on the thermoelectric properties in single-crystalline Bi nanowires

    SciTech Connect

    Chang, Taehoo; Kim, Jeongmin; Song, Min-Jung; Lee, Wooyoung

    2015-05-15

    The effects of proton irradiation on the thermoelectric properties of Bi nanowires (Bi-NWs) were investigated. Single crystalline Bi-NWs were grown by the on-film formation of nanowires method. The devices based on individual Bi-NWs were irradiated with protons at different energies. The total number of displaced atoms was estimated using the Kinchin-Pease displacement model. The electric conductivity and Seebeck coefficient in the Bi-NW devices were investigated before and after proton irradiation at different temperatures. Although the Seebeck coefficient remained stable at various irradiation energies, the electrical conductivity significantly declined with increasing proton energy up to 40 MeV.

  12. Phenomenological Spin Transport Theory Driven by Anomalous Nernst Effect

    NASA Astrophysics Data System (ADS)

    Taniguchi, Tomohiro

    2016-07-01

    Several experimental efforts such as material investigation and structure improvement have been made recently to find a large anomalous Nernst effect in ferromagnetic metals. Here, we develop a theory of spin transport driven by the anomalous Nernst effect in a diffusive ferromagnetic/nonmagnetic multilayer. Starting from a phenomenological formula of a spin-dependent electric current, the theoretical formulas of electric voltage and spin torque generated by the anomalous Nernst effect are derived. The magnitude of the electric voltage generated from the spin current via the inverse spin Hall effect is on the order of 0.1 µV for currently available experimental parameter values. The temperature gradient necessary to switch the magnetization is quite larger than the typical experimental value. The separation of the contributions of the Seebeck and transverse spin Seebeck effects is also discussed.

  13. Magnon-driven longitudinal spin Seebeck effect in F | N and N | F | N structures: Role of asymmetric in-plane magnetic anisotropy

    NASA Astrophysics Data System (ADS)

    Chotorlishvili, L.; Toklikishvili, Z.; Etesami, S. R.; Dugaev, V. K.; Barnaś, J.; Berakdar, J.

    2015-12-01

    The influence of an asymmetric in-plane magnetic anisotropy Kx ≠Ky on the thermally activated spin current is studied theoretically for two different systems: (i) the F | N system consisting of a ferromagnetic insulator (F) in a direct contact with a nonmagnetic metal (N) and (ii) the sandwich structure N | F | N consisting of a ferromagnetic insulating part sandwiched between two nonmagnetic metals. It is shown that when the difference between the temperatures of the two nonmagnetic metals in a N | F | N structure is not large, the spin pumping currents from the magnetic part to the nonmagnetic ones are equal in amplitude and have opposite directions, so only the spin torque current contributes to the total spin current. The spin current flows then from the nonmagnetic metal with the higher temperature to the nonmagnetic metal having a lower temperature. Its amplitude varies linearly with the difference in temperatures. In addition, we have found that if the magnetic anisotropy is in the layer plane, then the spin current increases with the magnon temperature, while in the case of an out-of-plane magnetic anisotropy the spin current decreases when the magnon temperature enhances. Enlarging the difference between the temperatures of the nonmagnetic metals, the linear response becomes important, as confirmed by analytical expressions inferred from the Fokker-Planck approach and by the results obtained upon a full numerical integration of the stochastic Landau-Lifshitz-Gilbert equation.

  14. Magnetic Nernst effect

    NASA Astrophysics Data System (ADS)

    Brechet, Sylvain D.; Ansermet, Jean-Philippe

    2015-09-01

    The thermodynamics of irreversible processes in continuous media predicts the existence of a magnetic Nernst effect that results from a magnetic analog to the Seebeck effect in a ferromagnet and magnetophoresis occurring in a paramagnetic electrode in contact with the ferromagnet. Thus, a voltage that has DC and AC components is expected across a Pt electrode as a response to the inhomogeneous magnetic induction field generated by magnetostatic waves of an adjacent YIG slab subject to a temperature gradient. The voltage frequency and dependence on the orientation of the applied magnetic induction field are quite distinct from that of spin pumping.

  15. Analysis of Residual Acceleration Effects on Transport and Segregation During Directional Solidification of Tin-Bismuth in the MEPHISTO Furnace Facility

    NASA Technical Reports Server (NTRS)

    Alexander J. Iwan D. (Principal Investigator)

    1996-01-01

    The objective of this work is to approach the problem of determining the transport conditions (and effects of residual acceleration) during the plane-front directional solidification of a tin-bismuth alloy under low gravity conditions. The work involves using a combination of 2- and 3-D numerical models, scaling analyses, ID models and the results of ground-based and low-gravity experiments. The latter are to be conducted during the MEPHISTO experiment scheduled for USMP-3 in early 1996. The models will be used to predict the response of the transport conditions and consequent solute segregation in directionally solidifying tin-bismuth melt. Real-time Seebeck voltage variations across a Sn-Bi melt during directional solidification in MEPHISTO on USMP-1 show a distinct variation which can be correlated with thruster firings. The Seebeck voltage measurement is related to the response of the instantaneous average melt composition at the melt-solid interface. This allows a direct comparison of numerical simulations with the Seebeck signals obtained on USMP-1. The effects of such accelerations on composition for a directionally solidifying Sn-Bi alloy have been simulated numerically. USMP-1 acceleration data was used to assist in our choice of acceleration magnitude and orientation. The results show good agreement with experimental observations. The USMP-3 experiments took place earlier this year (February 22 through March 6). There were several differences between the USMP-3 experiments as compared to USMP-1. Firstly a more concentrated alloy was solidified and, secondly, Primary Reaction Control System thruster burns were requested at particular times during four separate growth runs. This allowed us to monitor the response Seebeck response under well-characterized growth conditions. In addition, we carried out simulations during the experiment in order to interpret the Seebeck signal. Preliminary results are described here.

  16. Doping effects on thermoelectric properties of the off-stoichiometric Heusler compounds Fe{sub 2−x}V{sub 1+x}Al

    SciTech Connect

    Nishino, Y. Tamada, Y.

    2014-03-28

    The thermoelectric properties of Heusler-type Fe{sub 2−x}V{sub 1+x}Al{sub 1−y}Si{sub y} and Fe{sub 2−x}V{sub 1+x−y}Ti{sub y}Al alloys have been investigated to clarify which off-stoichiometric alloy, i.e., V-rich (x > 0) or V-poor (x < 0), is more effective in enhancing the Seebeck coefficient when doped by Si and Ti, while retaining a low electrical resistivity. Large Seebeck coefficients of −182 μV/K and 110 μV/K at 300 K are obtained for n-type Fe{sub 1.95}V{sub 1.05}Al{sub 0.97}Si{sub 0.03} and p-type Fe{sub 2.04}V{sub 0.93}Ti{sub 0.03}Al, respectively. When the Seebeck coefficient is plotted as a function of valence electron concentration (VEC), the VEC dependence for the doped off-stoichiometric alloys falls on characteristic curves depending on the off-stoichiometric composition x. It is concluded that a larger Seebeck coefficient with a negative sign can be obtained for the V-rich alloys rather than the V-poor alloys, whilst good p-type materials are always derived from the V-poor alloys. Substantial enhancements in the Seebeck coefficient for the off-stoichiometric alloys could be achieved by a favorable modification in the electronic structure around the Fermi level through the antisite V or Fe defect formation.

  17. Evaluation of Temperature-Dependent Effective Material Properties and Performance of a Thermoelectric Module

    NASA Astrophysics Data System (ADS)

    Chien, Heng-Chieh; Chu, En-Ting; Hsieh, Huey-Lin; Huang, Jing-Yi; Wu, Sheng-Tsai; Dai, Ming-Ji; Liu, Chun-Kai; Yao, Da-Jeng

    2013-07-01

    We devised a novel method to evaluate the temperature-dependent effective properties of a thermoelectric module (TEM): Seebeck coefficient ( S m), internal electrical resistance ( R m), and thermal conductance ( K m). After calculation, the effective properties of the module are converted to the average material properties of a p- n thermoelectric pillar pair inside the module: Seebeck coefficient ( S TE), electrical resistivity ( ρ TE), and thermal conductivity ( k TE). For a commercial thermoelectric module (Altec 1091) chosen to verify the novel method, the measured S TE has a maximum value at bath temperature of 110°C; ρ TE shows a positive linear trend dependent on the bath temperature, and k TE increases slightly with increasing bath temperature. The results show the method to have satisfactory measurement performance in terms of practicability and reliability; the data for tests near 23°C agree with published values.

  18. Anomalous Nernst Effect of Perpendicularly Magnetic Anisotropy TbFeCo Thin Films

    NASA Astrophysics Data System (ADS)

    Ando, Ryo; Komine, Takashi; Hasegawa, Yasuhiro

    2016-07-01

    In this study, we investigated anomalous Nernst effect (ANE) of perpendicularly magnetized TbFeCo thin films with various Tb content, and especially studied the relation between ANE and anomalous Hall effect. As a result, the hysteresis of anomalous Nernst coefficient showed the same behavior as that of anomalous Hall resistivity, and the sign of anomalous Nernst coefficient was consistent with that of anomalous Hall voltage in any Tb content, whereas the Seebeck coefficient and the resistivity were almost constant even if the applied magnetic field was varied. Taking into account of thermoelectric coefficient tensor, it was revealed that the off-diagonal thermopower corresponding to the ANE in TbFeCo thin films is the product of Hall angle and Seebeck coefficient.

  19. Harnessing Topological Band Effects in Bismuth Telluride Selenide for Large Enhancements in Thermoelectric Properties through Isovalent Doping.

    PubMed

    Devender; Gehring, Pascal; Gaul, Andrew; Hoyer, Alexander; Vaklinova, Kristina; Mehta, Rutvik J; Burghard, Marko; Borca-Tasciuc, Theodorian; Singh, David J; Kern, Klaus; Ramanath, Ganpati

    2016-08-01

    Dilute isovalent sulfur doping simultaneously increases electrical conductivity and Seebeck coefficient in Bi2 Te2 Se nanoplates, and bulk pellets made from them. This unusual trend at high electron concentrations is underpinned by multifold increases in electron effective mass attributable to sulfur-induced band topology effects, providing a new way for accessing a high thermoelectric figure-of-merit in topological-insulator-based nanomaterials through doping. PMID:27167512

  20. Thermoelectric effects in graphene nanostructures.

    PubMed

    Dollfus, Philippe; Hung Nguyen, Viet; Saint-Martin, Jérôme

    2015-04-10

    The thermoelectric properties of graphene and graphene nanostructures have recently attracted significant attention from the physics and engineering communities. In fundamental physics, the analysis of Seebeck and Nernst effects is very useful in elucidating some details of the electronic band structure of graphene that cannot be probed by conductance measurements alone, due in particular to the ambipolar nature of this gapless material. For applications in thermoelectric energy conversion, graphene has two major disadvantages. It is gapless, which leads to a small Seebeck coefficient due to the opposite contributions of electrons and holes, and it is an excellent thermal conductor. The thermoelectric figure of merit ZT of a two-dimensional (2D) graphene sheet is thus very limited. However, many works have demonstrated recently that appropriate nanostructuring and bandgap engineering of graphene can concomitantly strongly reduce the lattice thermal conductance and enhance the Seebeck coefficient without dramatically degrading the electronic conductance. Hence, in various graphene nanostructures, ZT has been predicted to be high enough to make them attractive for energy conversion. In this article, we review the main results obtained experimentally and theoretically on the thermoelectric properties of graphene and its nanostructures, emphasizing the physical effects that govern these properties. Beyond pure graphene structures, we discuss also the thermoelectric properties of some hybrid graphene structures, as graphane, layered carbon allotropes such as graphynes and graphdiynes, and graphene/hexagonal boron nitride heterostructures which offer new opportunities. Finally, we briefly review the recent activities on other atomically thin 2D semiconductors with finite bandgap, i.e. dichalcogenides and phosphorene, which have attracted great attention for various kinds of applications, including thermoelectrics. PMID:25779989

  1. Compensation of voltage drops in solid-state switches used with thermoelectric generators

    NASA Technical Reports Server (NTRS)

    Shimada, K.

    1972-01-01

    Seebeck effect solid state switch was developed eliminating thermoelectric generator switch voltage drops. Semiconductor switches were fabricated from materials with large Seebeck coefficients, arranged such that Seebeck potential is generated with such polarity that current flow is aided.

  2. Enhancement of thermospin effect in germanene based normal/ferromagnetic stub/normal junction

    NASA Astrophysics Data System (ADS)

    Zheng, Jun; Chi, Feng; Guo, Yong

    2015-11-01

    Spin thermoelectric effects in ferromagnetic (FM) germanene are theoretically investigated by using the nonequilibrium Green's function method. It is found that the spin Seebeck effect can be generated by temperature bias Δ T when a FM germanene is considered in the central region. However, the obtained spin resolved Seebeck coefficients is quite low with maximum value of S σ ≃ 700 μ V / K . The spin Seebeck effect is shown to increase enormously in different energy states with the assistance of electric field or stub structure. By modulating the geometric parameters of stub, the spin thermopower Ss has distinct peak values in the bulk states. Moreover, varying the Fermi energy within the bulk gap by the gate, Ss can be significantly enhanced by increasing the strength of electric field. The spin thermopower obtained by each method is predicted to be 2500 μ V / K , which is more than 300% larger relative to the case without electric field or stub. In addition, the magnitude and sign of spin thermopower can be manipulated by adjusting the Fermi energy. The results show that such FM germanene stub device exhibits much better thermoelectric performance and may be used as a wide energy range tunable spin thermoelectric generator.

  3. Effective material properties of thermoelectric composites with elliptical fibers

    NASA Astrophysics Data System (ADS)

    Wang, Yi-Ze

    2015-06-01

    In the present work, the effective material properties of thermoelectric composites with elliptical fibers are studied. Explicit solutions are derived by the conformal mapping function and Mori-Tanaka method. Numerical simulations are performed to present the behaviors of normalized effective material constants. From the results, it can be observed that both the effective electric and thermal conductivities can be reduced by increasing the filling ratio and a/ b. Such influences can also be found for the effective thermoelectric figure of merit. But they are different from those on the effective Seebeck and Peltier coefficients.

  4. Effect of pressure on electronic and thermoelectric properties of magnesium silicide: A density functional theory study

    NASA Astrophysics Data System (ADS)

    Kulwinder, Kaur; Ranjan, Kumar

    2016-05-01

    We study the effect of pressure on electronic and thermoelectric properties of Mg2Si using the density functional theory and Boltzmann transport equations. The variation of lattice constant, band gap, bulk modulus with pressure is also analyzed. Further, the thermoelectric properties (Seebeck coefficient, electrical conductivity, electronic thermal conductivity) have been studied as a function of temperature and pressure up to 1200 K. The results show that Mg2Si is an n-type semiconductor with a band gap of 0.21 eV. The negative value of the Seebeck coefficient at all pressures indicates that the conduction is due to electrons. With the increase in pressure, the Seebeck coefficient decreases and electrical conductivity increases. It is also seen that, there is practically no effect of pressure on the electronic contribution of thermal conductivity. The paper describes the calculation of the lattice thermal conductivity and figure of merit of Mg2Si at zero pressure. The maximum value of figure of merit is attained 1.83×10‑3 at 1000 K. The obtained results are in good agreement with the available experimental and theoretical results. Project supported by the Council of Scientific & Industrial Research (CSIR), India.

  5. Synthetic conditions and their doping effect on {Beta}-K{sub 2}Bi{sub 8}Se{sub 13}.

    SciTech Connect

    Kyratsi, Th.; Kika, I.; Hatzikraniotis, E.; Paraskevopoulos, K. M.; Chrissafis, K.; Kanatzidis, M. G.

    2009-04-01

    In this work the synthetic conditions for K{sub 2}Bi{sub 8}Se{sub 13} and their effect on its thermoelectric properties were investigated. K{sub 2}Bi{sub 8}Se{sub 13} was prepared as a single phase using K{sub 2}Se and Bi{sub 2}Se{sub 3} as starting materials in a furnace or via a reaction using direct flame, followed by remelting or annealing. Seebeck coefficient measurements showed that the doping level in the material is sensitive to the synthetic conditions. Higher synthesis temperatures as well as the flame reaction technique followed by annealing gave more homogenous samples with higher Seebeck coefficient. IR optical spectroscopic measurements showed a wide range of doping level achieved among the different synthetic conditions. These findings suggest that synthetic conditions can act as a useful tool for the optimization of the thermoelectric properties of these materials.

  6. Ab initio optimization of phonon drag effect for lower-temperature thermoelectric energy conversion.

    PubMed

    Zhou, Jiawei; Liao, Bolin; Qiu, Bo; Huberman, Samuel; Esfarjani, Keivan; Dresselhaus, Mildred S; Chen, Gang

    2015-12-01

    Although the thermoelectric figure of merit zT above 300 K has seen significant improvement recently, the progress at lower temperatures has been slow, mainly limited by the relatively low Seebeck coefficient and high thermal conductivity. Here we report, for the first time to our knowledge, success in first-principles computation of the phonon drag effect--a coupling phenomenon between electrons and nonequilibrium phonons--in heavily doped region and its optimization to enhance the Seebeck coefficient while reducing the phonon thermal conductivity by nanostructuring. Our simulation quantitatively identifies the major phonons contributing to the phonon drag, which are spectrally distinct from those carrying heat, and further reveals that although the phonon drag is reduced in heavily doped samples, a significant contribution to Seebeck coefficient still exists. An ideal phonon filter is proposed to enhance zT of silicon at room temperature by a factor of 20 to ∼ 0.25, and the enhancement can reach 70 times at 100 K. This work opens up a new venue toward better thermoelectrics by harnessing nonequilibrium phonons. PMID:26627231

  7. Anomalous effect of vanadium boride seeding on thermoelectric properties of YB{sub 22}C{sub 2}N

    SciTech Connect

    Prytuliak, A.; Maruyama, S.; Mori, T.

    2013-05-15

    Highlights: ► We doped YB{sub 22}C{sub 2}N; the long awaited n-type counterpart to p-type boron carbide. ► VB{sub 2} seeding of YB{sub 22}C{sub 2}N showed striking results. ► Thermal treatment effects led to VB{sub 2} being intrinsically doped. ► Large increase of both Seebeck coefficient and electrical conductivity was obtained. - Abstract: Vanadium boride seeded YB{sub 22}C{sub 2}N were synthesized and the thermoelectric properties investigated. YB{sub 22}C{sub 2}N is representative of the series of rare earth borocarbonitrides which is the potential long awaited n-type counterpart to p-type boron carbide. VB{sub 2} seeded samples of YB{sub 22}C{sub 2}N were prepared using VB{sub 2} directly as an initial additive and V{sub 2}O{sub 3} which also results in formation of vanadium diboride in the final product. The resistivity and Seebeck coefficient of samples were measured in the temperature range of 323 K to 1073 K. A dramatic effect of thermal treatment on the Seebeck coefficient of VB{sub 2} seeded samples was observed, and it is indicated that there is possible partial intrinsic doping of vanadium into YB{sub 22}C{sub 2}N. VB{sub 2} is revealed to be a promising additive to improve the thermoelectric properties of YB{sub 22}C{sub 2}N. An enhancement of more than 220% of the maximum absolute value of the Seebeck coefficient was obtained while the resistivity was also reduced considerably.

  8. Thermoelectric and Seebeck coefficients of granular metals.

    SciTech Connect

    Glatz, A.; Beloborodov, I. S.; Materials Science Division; California State Univ.

    2009-01-01

    In this work we present a detailed study and derivation of the thermopower and thermoelectric coefficient of nanogranular metals at large tunneling conductance between the grains, g{sub T} >> 1. An important criterion for the performance of a thermoelectric device is the thermodynamic figure of merit which is derived using the kinetic coefficients of granular metals. All results are valid at intermediate temperatures, E{sub c} >> T/g{sub T} > {delta}, where {delta} is the mean energy-level spacing for a single grain and E{sub c} is its charging energy. We show that the electron-electron interaction leads to an increase in the thermopower with decreasing grain size and discuss our results in light of future generation thermoelectric materials for low-temperature applications. The behavior of the figure of merit depending on system parameters such as grain size, tunneling conductance, and temperature is presented.

  9. Giant intrinsic thermomagnetic effects in thin MgO magnetic tunnel junctions

    NASA Astrophysics Data System (ADS)

    Teixeira, J. M.; Costa, J. D.; Ventura, J.; Fernandez-Garcia, M. P.; Azevedo, J.; Araujo, J. P.; Sousa, J. B.; Wisniowski, P.; Cardoso, S.; Freitas, P. P.

    2013-05-01

    An intrinsic spin-dependent Seebeck effect in the linear tunneling transport regime of magnetic tunneling junctions (MTJs) was discovered recently. This effect leads to a nonlinear correction of Ohm's law in the dc response. We analyze this intrinsic magneto-thermoelectrical effect for MTJs with different MgO barrier (tb=0.7-1.35 nm) thicknesses. We report strong intrinsic effects in MTJs with thin MgO barriers (1189%), upon reversal of the magnetization of the two CoFeB layers. Such large effects are promising for useful spin caloritronic devices, integrating charge, heat, and spin tunnel transport.

  10. Improved thermoelectric cooling based on the Thomson effect

    NASA Astrophysics Data System (ADS)

    Snyder, G. Jeffrey; Khanna, Raghav; Toberer, Eric S.; Heinz, Nicholas A.; Seifert, Wolfgang

    2016-05-01

    Traditional thermoelectric cooling relies on the Peltier effect which produces a temperature drop limited by the figure of merit, zT. This cooling limit is not required from classical thermodynamics but can be traced to problems of thermoelectric compatibility. Alternatively, if a thermoelectric cooler can be designed to achieve full thermoelectric compatibility, lower temperature can be achieved even if the zT is low. In such a device the Thomson effect plays an important role. We present the theoretical concept of a "Thomson cooler," for cryogenic cooling which is designed to maintain thermoelectric compatibility and we derive the requirements for the Seebeck coefficient.

  11. A systematic study on the effect of electron beam irradiation on structural, electrical, thermo-electric power and magnetic property of LaCoO3

    NASA Astrophysics Data System (ADS)

    Benedict, Christopher J.; Rao, Ashok; Sanjeev, Ganesh; Okram, G. S.; Babu, P. D.

    2016-01-01

    In this communication, the effect of electron beam irradiation on the structural, electrical, thermo-electric power and magnetic properties of LaCoO3 cobaltites have been investigated. Rietveld refinement of XRD data reveals that all samples are single phased with rhombohedral structure. Increase in electrical resistivity data is observed with increase in dosage of electron beam irradiation. Analysis of the measured electrical resistivity data indicates that the small polaron hopping model is operative in the high temperature regime for all samples. The Seebeck coefficient (S) of the pristine and the irradiated samples exhibits a crossover from positive to negative values, and a colossal value of Seebeck coefficient (32.65 mV/K) is obtained for pristine sample, however, the value of S decreases with increase in dosage of irradiation. The analysis of Seebeck coefficient data confirms that the small polaron hopping model is operative in the high temperature region. The magnetization results give clear evidence of increase in effective magnetic moment due to increase in dosage of electron beam irradiation.

  12. Effect of magnetic anisotropy on spin-dependent thermoelectric effects in nanoscopic systems

    NASA Astrophysics Data System (ADS)

    Misiorny, Maciej; Barnaś, Józef

    2015-04-01

    Conventional and spin-related thermoelectric effects in electronic transport through a nanoscopic system exhibiting magnetic anisotropy, with both uniaxial and transverse components, are studied theoretically in the linear-response regime. In particular, a magnetic tunnel junction with a large-spin impurity, either a magnetic atom or a magnetic molecule, embedded in the barrier is considered as an example. Owing to magnetic interaction with the impurity, conduction electrons traversing the junction can scatter on the impurity, which effectively can lead to angular momentum and energy exchange between the electrons and the impurity. As we show, such processes have a profound effect on the thermoelectric response of the system. Specifically, we present a detailed analysis of charge, spin, and thermal conductance, together with the Seebeck and spin Seebeck coefficients (thermopowers). Since the scattering mechanism also involves processes when electrons are inelastically scattered back to the same electrode, one can expect the flow of spin and energy also in the absence of charge transport through the junction. This, in turn, results in a finite spin thermopower, and the magnetic anisotropy plays a key role for this effect to occur.

  13. Galvanomagnetic effects in Gd and Zn-substituted Bi{sub 2}Sr{sub 2}Ca{sub 1{minus}x}Gd{sub x}(Cu{sub 1{minus}y}Zn{sub y}){sub 2}O{sub 8+{delta}}

    SciTech Connect

    Ilonca, G.; Pop, A.V.; Tarta, G.; Jurcut, T.; Deltour, R.

    1999-09-10

    The authors had performed a study on magnetoresistivity Hall, Nernst and Seebeck effects in the mixed and normal state for Bi2212 bulk with Gd (0 {le} x {le} 0.50) and Zn (0 {le} y {le} 0.03) prepared by the conventional solid state reaction method in magnetic fields between 0 and 5 T and in the temperature range 5--300 K. The critical temperatures, the Hall concentration, the Nernst and Seebeck coefficients depend strongly on the Zn and Gd contents in the samples. Also, they have found an anomalous suppression of superconductivity at x = 0.30--0.35 and y = 0.025--0.030, when the hole concentration per Cu is p {approximately} 1/8 and the transport properties exhibit less metallic behavior than usual. There is a possibility that a kind of order of holes and/or spins is stabilized owing to pinning by Zn, as in the La-based cuprate.

  14. Photo-controllable thermoelectric properties with reversibility and photo-thermoelectric effects of tungsten trioxide accompanied by its photochromic phenomenon

    NASA Astrophysics Data System (ADS)

    Azuma, Chiori; Kawano, Takuto; Kakemoto, Hirofumi; Irie, Hiroshi

    2014-11-01

    The addition of photo-controllable properties to tungsten trioxide (WO3) is of interest for developing practical applications of WO3 as well as for interpreting such phenomena from scientific viewpoints. Here, a sputtered crystalline WO3 thin film generated thermoelectric power due to ultraviolet (UV) light-induced band-gap excitation and was accompanied by a photochromic reaction resulting from generating W5+ ions. The thermoelectric properties (electrical conductivity (σ) and Seebeck coefficient (S)) and coloration of WO3 could be reversibly switched by alternating the external stimulus between UV light irradiation and dark storage. After irradiating the film with UV light, σ increased, whereas the absolute value of S decreased, and the photochromic (coloration) reaction was detected. Notably, the opposite behavior was exhibited by WO3 after dark storage, and this reversible cycle could be repeated at least three times. Moreover, photo-thermoelectric effects (photo-conductive effect (photo-conductivity, σphoto) and photo-Seebeck effect (photo-Seebeck coefficient, Sphoto)) were also detected in response to visible-light irradiation of the colored WO3 thin films. Under visible-light irradiation, σphoto and the absolute value of Sphoto increased and decreased, respectively. These effects are likely attributable to the excitation of electrons from the mid-gap visible light absorption band (W5+ state) to the conduction band of WO3. Our findings demonstrate that the simultaneous, reversible switching of multiple properties of WO3 thin film is achieved by the application of an external stimulus and that this material exhibits photo-thermoelectric effects when irradiated with visible-light.

  15. Photo-controllable thermoelectric properties with reversibility and photo-thermoelectric effects of tungsten trioxide accompanied by its photochromic phenomenon

    SciTech Connect

    Azuma, Chiori; Kawano, Takuto; Kakemoto, Hirofumi; Irie, Hiroshi

    2014-11-07

    The addition of photo-controllable properties to tungsten trioxide (WO{sub 3}) is of interest for developing practical applications of WO{sub 3} as well as for interpreting such phenomena from scientific viewpoints. Here, a sputtered crystalline WO{sub 3} thin film generated thermoelectric power due to ultraviolet (UV) light-induced band-gap excitation and was accompanied by a photochromic reaction resulting from generating W{sup 5+} ions. The thermoelectric properties (electrical conductivity (σ) and Seebeck coefficient (S)) and coloration of WO{sub 3} could be reversibly switched by alternating the external stimulus between UV light irradiation and dark storage. After irradiating the film with UV light, σ increased, whereas the absolute value of S decreased, and the photochromic (coloration) reaction was detected. Notably, the opposite behavior was exhibited by WO{sub 3} after dark storage, and this reversible cycle could be repeated at least three times. Moreover, photo-thermoelectric effects (photo-conductive effect (photo-conductivity, σ{sub photo}) and photo-Seebeck effect (photo-Seebeck coefficient, S{sub photo})) were also detected in response to visible-light irradiation of the colored WO{sub 3} thin films. Under visible-light irradiation, σ{sub photo} and the absolute value of S{sub photo} increased and decreased, respectively. These effects are likely attributable to the excitation of electrons from the mid-gap visible light absorption band (W{sup 5+} state) to the conduction band of WO{sub 3}. Our findings demonstrate that the simultaneous, reversible switching of multiple properties of WO{sub 3} thin film is achieved by the application of an external stimulus and that this material exhibits photo-thermoelectric effects when irradiated with visible-light.

  16. Rubbing effect on surface morphology and thermoelectric properties of TTF-TCNQ thin films

    NASA Astrophysics Data System (ADS)

    Tamayo, E.; Hayashi, K.; Shinano, T.; Miyazaki, Y.; Kajitani, T.

    2010-05-01

    Thin films of tetrathiofulvalene-tetracyanoquinodimethane (TTF-TCNQ), a typical organic material of charge transfer salts, were prepared on glass substrates by evaporation using TTF-TCNQ powder. The rubbing effect on the surface morphology and thermoelectric properties was studied. TTF-TCNQ films exhibited a bush-like disordered growth on the as-received glass substrate, whereas those on the rubbed glass substrate had extremely flat surfaces tiled with small rectangular TTF-TCNQ single crystals. Due to the ordered alignment of TTF-TCNQ tiles, improvement in the electrical conductivity and enhancement of the Seebeck coefficient were achieved.

  17. Thermoelectric properties of single-wall carbon nanotube films: Effects of diameter and wet environment

    NASA Astrophysics Data System (ADS)

    Hayashi, Daisuke; Ueda, Tomohiro; Nakai, Yusuke; Kyakuno, Haruka; Miyata, Yasumitsu; Yamamoto, Takahiro; Saito, Takeshi; Hata, Kenji; Maniwa, Yutaka

    2016-02-01

    The Seebeck coefficient S and the electrical resistivity ρ of single-wall carbon nanotube (SWCNT) films were investigated as a function of the SWCNT diameter and carrier concentration. The S and ρ significantly changed in humid environments through p-type carrier doping. Experiments, combined with theoretical simulations based on the non-equilibrium Green’s function theory, indicated that the power factor P can be increased threefold by the enrichment of semiconducting SWCNTs, but the nanotube diameter has little effect. The improvement of the film resistivity strongly enhances the film thermoelectric performance, manifested as increasing the value of P above 1200 µW/(m·K2).

  18. Large extrinsic spin Hall effect in Au-Cu alloys by extensive atomic disorder scattering

    NASA Astrophysics Data System (ADS)

    Zou, L. K.; Wang, S. H.; Zhang, Y.; Sun, J. R.; Cai, J. W.; Kang, S. S.

    2016-01-01

    Spin Hall angle, which denotes the conversion efficiency between spin and charge current, is a key parameter in the pure spin current phenomenon. The search for materials with large spin Hall angle is indeed important for scientific interest and potential application in spintronics. Here the large enhanced spin Hall effect (SHE) of Au-Cu alloy is reported by investigating the spin Seebeck effect, spin Hall anomalous Hall effect, and spin Hall magnetoresistance of the Y3F e5O12 (YIG)/A uxC u1 -x hybrid structure over the full composition. At the near equiatomic Au-Cu composition with maximum atomic disorder scattering, the spin Hall angle of the Au-Cu alloy increases by two to three times together with a moderate spin diffusion length in comparison with Au. The longitudinal spin Seebeck voltage and the spin Hall magnetoresistance ratio also increase by two to three times. More importantly, no evidence of anomalous Hall effect is observed in all YIG/Au-Cu samples, in contrast to the cases of other giant SHE materials Pt(Pd), Ta, and W. This behavior makes Au-Cu free from any suspicion of the magnetic proximity effect involved in the hybrid structure, and thus the Au-Cu alloy can be an ideal material for pure spin current study.

  19. A Quantitative Model for the Thermocouple Effect Using Statistical and Quantum Mechanics

    NASA Astrophysics Data System (ADS)

    Bramley, Paul; Clark, Stewart

    2003-09-01

    This paper employs statistical and quantum mechanics to develop a model for the mechanism underlying the Seebeck effect. The conventional view of the equilibrium criterion for valence electrons in a material is that the Fermi Energy should be constant throughout the system. However, this criterion is an approximation and it is shown to be inadequate for thermocouple systems. An improved equilibrium criterion is developed by applying statistical and quantum mechanics to determine the total flow of electrons across an arbitrary boundary within a system. Dynamic equilibrium is then considered to be the situation where the Fermi Energy either side of the boundary is such that the flow of electrons in each direction is the same. This equilibrium criterion is then applied to the conditions along the thermocouple wires and at the junctions in order to generate a model for the Seebeck effect. The equations involved for calculating the electronic structure of a material cannot be solved analytically, so a solution is achieved using numeric models employing CASTEP code running on a Sun Beowulf cluster and iterative algorithms written in the Excel™ VBA language on a PC. The model is used to calculate the EMF versus temperature function for the gold versus platinum thermocouple, which is then compared with established experimental data.

  20. Thermal Cycling Effects on the Thermoelectric Properties of n-Type In, Ce based Skutterudite Compounds

    SciTech Connect

    Biswas, Krishnendu; Subramanian, Mas A.; Good, Morris S.; Roberts, Kamandi C.; Hendricks, Terry J.

    2012-06-14

    N-type In-filled CoSb3 are known skutterudite compounds that have shown promising thermoelectric (TE) properties resulting in high dimensionless figure of merit values at elevated temperatures. Their use in various waste heat recovery applications will require that they survive and operate after exposure to harsh thermal cycling environments. This research focused on uncovering the thermal cycling effects on thermoelectric properties of n-type In0.2Co4Sb12 and In0.2Ce0.15Co4Sb12 skutterudite compositions as well as quantifying their temperature-dependent structural properties (elastic modulus, shear modulus, and Poisson's ratio). It was observed that the Seebeck coefficient and resistivity increased only slightly in the double-filled In,Ce skutterudite materials upon thermal cycling. In the In-filled skutterudites the Seebeck coefficient remained approximately the same on thermal cycling, while electrical resistivity increased significantly after thermal cycling. Results also show that thermal conductivity marginally decreases in the case of In-filled skutterudites, whereas the reduction is more pronounced in In, Ce-based skutterudite compounds. The possible reason for this kind of reduction can be attributed to grain pinning effects due to formation of nano inclusions. High temperature structural property measurements (i.e., Young's modulus and shear modulus) are also reported and the results show that these structural properties decrease slowly as temperature increases and the compounds are structurally stable after numerous thermal cycles.

  1. Giant spin-dependent thermoelectric effect in magnetic tunnel junctions.

    PubMed

    Lin, Weiwei; Hehn, Michel; Chaput, Laurent; Negulescu, Béatrice; Andrieu, Stéphane; Montaigne, François; Mangin, Stéphane

    2012-01-01

    Thermoelectric effects in magnetic nanostructures and the so-called spin caloritronics are attracting much interest. Indeed it provides a new way to control and manipulate spin currents, which are key elements of spin-based electronics. Here we report on a giant magnetothermoelectric effect in a magnetic tunnel junction. The thermovoltage in this geometry can reach 1 mV. Moreover a magnetothermovoltage effect could be measured with ratio similar to the tunnel magnetoresistance ratio. The Seebeck coefficient can then be tuned by changing the relative magnetization orientation of the two magnetic layers in the tunnel junction. Therefore, our experiments extend the range of spintronic devices application to thermoelectricity and provide a crucial piece of information for understanding the physics of thermal spin transport. PMID:22434187

  2. Growth parameters effect on the electric and thermoelectric characteristics of Bi 2Se 3 thin films grown by MOCVD system

    NASA Astrophysics Data System (ADS)

    Al Bayaz, A.; Giani, A.; Artaud, M. C.; Foucaran, A.; Pascal-Delannoy, F.; Boyer, A.

    2002-06-01

    Bi 2Se 3 thin films were grown by metal organic chemical vapour deposition (MOCVD) on pyrex substrate in an horizontal reactor using Trimethylbismuth (TMBi) and Diethylselinium (DESe) as metal-organic sources. The effect of the growth parameters such as substrate temperature, Tg, and TMBi partial pressure, PTMBi, on the structural, electrical and thermoelectrical properties of Bi 2Se 3 films, has been investigated. We noticed that a high growth temperature is very important for a good orientation of crystallites, which can be directly related to the best values of Hall mobility and Seebeck coefficient found. Therefore, a large stability of the reactions over the substrates with following growth conditions: 455°C⩽ Tg⩽485°C,0.5×10 -4⩽ PTMBi⩽1×10 -4 atm and a total hydrogen flow rate DT=3 slm, is achieved. In these optimal growth conditions, we found a better crystalline structure of Bi 2Se 3 thin films using X-ray diffraction. Thus, these layers always displayed n-type conduction using Hall effect, with carrier concentration close to 2×10 19 cm -3 and maximum values of Hall mobility and Seebeck coefficient of μ=247 cm 2/V s and | α|=120 μV/K respectively. Then, these films appear to be very promising for thermoelectric applications.

  3. Influence of Thallium on the Shubnikov - de Haas effect and Thermoelectric Properties of Sb2Te3 and Bi2Se3

    NASA Astrophysics Data System (ADS)

    Kulbachinskii, V. A.; Kudryashov, A. A.; Kytin, V. G.

    2014-12-01

    Influence of Tl-doping on the Shubnikov de Haas effect (SdH) at T=4.2 K in magnetic field up to 38 T of p-Sb2-xTlxTe3 (x=0; 0.005; 0.015; 0.05) and n-Bi2-xTlxSe3 (x=0, 0.01; 0.02; 0.04; 0.06) single crystals has been investigated. By increasing the Tl content, the frequency of the SdH effect and hence the extremal cross-sections of the Fermi-surface decreases in both materials. The hole concentration decreases in Sb2-xTlxTe3 due to a donor effect of Tl and the electron concentration decreases in n-Bi2-xTlxSe3 due to an acceptor effect of Tl. Temperature dependence of the Seebeck coefficient S, electrical conductivity σ, thermal conductivity k and the figure of merit ZT single crystals were measured in the temperature range 77 K - 300 K. The values of k and σ decrease due to Tl doping in Sb2-xTlxTe3 and n-Bi2-xTlxSe3 and the Seebeck coefficient S for all compositions increases in the whole temperature range. The figure of merit ZT increases in both materials. The preferential scattering mechanism in Tl-doped samples changes from the acoustic phonon scattering to the ionized impurity scattering.

  4. Thermoelectric effect enhanced by resonant states in graphene

    NASA Astrophysics Data System (ADS)

    Inglot, M.; Dyrdał, A.; Dugaev, V. K.; Barnaś, J.

    2015-03-01

    Thermoelectric effects in graphene are considered theoretically with particular attention paid to the role of resonant scattering on impurities. Using the T -matrix method we calculate the impurity resonant states and the momentum relaxation time due to scattering on impurities. The Boltzmann kinetic equation is used to determine the thermoelectric coefficients. It is shown that the resonant impurity states near the Fermi level give rise to a resonant enhancement of the Seebeck coefficient and figure of merit Z T . The Wiedemann-Franz ratio deviates from that known for ordinary metals, where this ratio is constant and equal to the Lorentz number. This deviation appears for small chemical potentials and in the vicinity of the resonant states. In the limit of a constant relaxation time, this ratio has been calculated analytically for μ =0 .

  5. Competing spin pumping effects in magnetic hybrid structures

    NASA Astrophysics Data System (ADS)

    Azevedo, A.; Alves Santos, O.; Fonseca Guerra, G. A.; Cunha, R. O.; Rodríguez-Suárez, R.; Rezende, S. M.

    2014-02-01

    Pure spin current can be detected by its conversion into charge current in nanometer thick nonmagnetic metal layer with large spin-orbit coupling by means of the inverse spin Hall effect (ISHE). Recently, it has been shown that the metallic ferromagnet Permalloy (Py) can also be used as spin current detector in experiments in which an ISHE voltage is created in a Py layer in contact with the insulating ferromagnet yttrium iron garnet (YIG) under a thermal gradient in the longitudinal spin Seebeck configuration. Here, we report experiments with microwave driven spin pumping in heterostructures made with single crystal YIG film and a nanometer thick Py or Pt layer that show that Py behaves differently than nonmagnetic metals as a spin current detector. The results are attributed to the competition between the spin currents generated by the dynamics of the magnetizations in YIG and in Py, which are exchange coupled at the interface.

  6. Reciprocal spin Hall effects in conductors with strong spin-orbit coupling: a review

    NASA Astrophysics Data System (ADS)

    Niimi, Yasuhiro; Otani, YoshiChika

    2015-12-01

    Spin Hall effect and its inverse provide essential means to convert charge to spin currents and vice versa, which serve as a primary function for spintronic phenomena such as the spin-torque ferromagnetic resonance and the spin Seebeck effect. These effects can oscillate magnetization or detect a thermally generated spin splitting in the chemical potential. Importantly this conversion process occurs via the spin-orbit interaction, and requires neither magnetic materials nor external magnetic fields. However, the spin Hall angle, i.e. the conversion yield between the charge and spin currents, depends severely on the experimental methods. Here we discuss the spin Hall angle and the spin diffusion length for a variety of materials including pure metals such as Pt and Ta, alloys and oxides determined by the spin absorption method in a lateral spin valve structure.

  7. Large inverse spin Hall effect in the antiferromagnetic metal Ir20Mn80

    NASA Astrophysics Data System (ADS)

    Mendes, J. B. S.; Cunha, R. O.; Alves Santos, O.; Ribeiro, P. R. T.; Machado, F. L. A.; Rodríguez-Suárez, R. L.; Azevedo, A.; Rezende, S. M.

    2014-04-01

    A spin current is usually detected by converting it into a charge current through the inverse spin Hall effect (ISHE) in thin layers of a nonmagnetic metal with large spin-orbit coupling, such as Pt, Pd, and Ta. Here we demonstrate that Ir20Mn80, a high-temperature antiferromagnetic metal that is commonly employed in spin-valve devices, exhibits a large inverse spin Hall effect, as recently predicted theoretically. We present results of experiments in which the spin currents are generated either by microwave spin pumping or by the spin Seebeck effect in bilayers of singe-crystal yttrium iron garnet (YIG)/Ir20Mn80 and compare them with measurements in YIG/Pt bilayers. The results of both measurements are consistent, showing that Ir20Mn80 has a spin Hall angle similar to Pt, and that it is an efficient spin-current detector.

  8. Reciprocal spin Hall effects in conductors with strong spin-orbit coupling: a review.

    PubMed

    Niimi, Yasuhiro; Otani, YoshiChika

    2015-12-01

    Spin Hall effect and its inverse provide essential means to convert charge to spin currents and vice versa, which serve as a primary function for spintronic phenomena such as the spin-torque ferromagnetic resonance and the spin Seebeck effect. These effects can oscillate magnetization or detect a thermally generated spin splitting in the chemical potential. Importantly this conversion process occurs via the spin-orbit interaction, and requires neither magnetic materials nor external magnetic fields. However, the spin Hall angle, i.e. the conversion yield between the charge and spin currents, depends severely on the experimental methods. Here we discuss the spin Hall angle and the spin diffusion length for a variety of materials including pure metals such as Pt and Ta, alloys and oxides determined by the spin absorption method in a lateral spin valve structure. PMID:26513299

  9. Effect of Heat Treatment in Air on Thermoelectric Properties of Polycrystalline Type-I Silicon-Based Clathrate: Ba8Al15Si31

    NASA Astrophysics Data System (ADS)

    Anno, Hiroaki; Shirataki, Ritsuko

    2015-06-01

    The effect of heat treatment in air on the thermoelectric properties was investigated for polycrystalline Ba8Al15Si31, where the Al content is almost at the maximum in the Ba8Al x Si46- x system, to evaluate the thermal stability in air at high temperatures, which is indispensable for practical use in thermoelectric applications. Samples were prepared by combining arc melting and spark plasma sintering techniques. Heat treatments were performed in air at 873 K for 10 days and 20 days. The Seebeck coefficient, electrical conductivity, and thermal conductivity were measured before and after the heat treatments. The microstructure and chemical composition were also analyzed before and after the heat treatments, using scanning electron microscopy with energy-dispersive x-ray spectroscopy. Although an oxidation layer was formed on the surface by the heat treatment in air, the chemical composition of the interior of Ba8Al15Si31 was found to be stable in air at 873 K for 10 days and 20 days. The Seebeck coefficient, the electrical conductivity, and the thermal conductivity were found to be almost unchanged after the heat treatment, indicating that Ba8Al15Si31 clathrate is promising as a thermoelectric material with high thermal stability for use in air at 873 K.

  10. Effects of Thallium Doping on the Transport Properties of Bi2Te3 Alloy

    NASA Astrophysics Data System (ADS)

    Yao, L.; Wu, F.; Wang, X. X.; Cao, R. J.; Li, X. J.; Hu, X.; Song, H. Z.

    2016-02-01

    Thallium-doped Tl x Bi2-x Te3 (x = 0.0, 0.05, 0.1, and 0.2) nanopowders were synthesized by the hydrothermal method. The doping effect of thallium on the morphologies of the synthesized nanopowders was investigated. It was found that the doping of thallium can significantly change the morphologies of the synthesized nanopowders. The synthesized nanopowders were hot-pressed into bulk pellets and the doping effects of thallium on the transport properties of these pellets were investigated. The results show that the doping of thallium can enhance the Seebeck coefficient but increase the electrical resistivity. Moreover, the power factors of the thallium-doped samples decrease with the increasing of the thallium doping level as compared with the un-doped sample. This is attributed to the increase of the electrical resistivity and the disappearing of the flower-like morphologies of the doped nanopowders.