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165 results on '"Reith, Heiko"'

1. Multiferroic Microstructure Created from Invariant Line Constraint

Author

Kar, Satyakam, Ikeda, Yuki, Nielsch, Kornelius, Reith, Heiko, Maaß, Robert, and Fähler, Sebastian

Subjects
Condensed Matter - Materials Science, Condensed Matter - Mesoscale and Nanoscale Physics
Abstract

Ferroic materials enable a multitude of emerging applications, and optimum functional properties are achieved when ferromagnetic and ferroelectric properties are coupled to a first-order ferroelastic transition. In bulk materials, this first-order transition involves an invariant habit plane, connecting coexisting phases: austenite and martensite. Theory predicts that this plane should converge to a line in thin films, but experimental evidence is missing. Here, we analyze the martensitic and magnetic microstructure of a freestanding epitaxial magnetic shape memory film. We show that the martensite microstructure is determined by an invariant line constraint using lattice parameters of both phases as the only input. This line constraint explains most of the observable features, which differ fundamentally from bulk and constrained films. Furthermore, this finite-size effect creates a remarkable checkerboard magnetic domain pattern through multiferroic coupling. Our findings highlight the decisive role of finite-size effects in multiferroics., Comment: 27 pages, 6 figures

Published
2024

3. Probing the carrier dynamics of polymer composites with single and hybrid carbon nanotube fillers for improved thermoelectric performance

Author

Konidakis, Ioannis, Krause, Beate, Park, Gyu-Hyeon, Pulumati, Nithin, Reith, Heiko, Pötschke, Petra, and Stratakis, Emmanuel

Subjects
Physics - Applied Physics, Condensed Matter - Materials Science
Abstract

The incorporation of carbon nanotubes (CNTs) within polymer hosts offers a great platform for the development of advanced thermoelectric (TE) composite materials. Over the years, several CNT/polymer composite formulations have been investigated on an effort to maximize the TE performance. Meanwhile, several studies focused on the decay dynamics of the charged excitons within CNTs itself and therefrom derived structures, aiming to investigate the lifetimes and the corresponding recombination processes of free charge carriers. The latter physical phenomena play a crucial role in the performance of various types of energy converting and scavenging materials. Nevertheless, up to this date, there is no systematic study on the combination of TE parameters and the critical charge carrier dynamics within CNT containing TE polymer composites. Herein, a variety of composites with single and hybrid CNT fillers based on polycarbonate (PC) and polyether ether ketone (PEEK) polymer matrices were prepared by melt-mixing in small scale. At the same loading, the addition of single fillers in PC results in higher Seebeck coefficients and similar conductivities when compared to the use of hybrid filler systems. In contrast, with hybrid filler systems in PEEK composites, higher power factors could be reached than in single filler composites. Moreover, the PC-based composites are studied using ultrafast laser time-resolved transient absorption spectroscopy (TAS), for the investigation of the exciton lifetimes and the physical origins of free charge carrier transport within the TE films. The findings of this study reveal interesting links between the TE parameters and the obtained charge carrier dynamics.

Published
2022
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4. Fluctuation-Dissipation in Thermoelectrics

Author

Tran, Ngoc Anh Minh, Dutt, Aditya Savitha, Pulumati, Nithin Bharadwaj, Reith, Heiko, Hu, Anjun, Dumont, Alexandre, Nielsch, Kornelius, Tremblay, André-Marie, Schierning, Gabi, Reulet, Bertrand, and Szkopek, Thomas

Subjects
Condensed Matter - Materials Science, Condensed Matter - Mesoscale and Nanoscale Physics, Condensed Matter - Statistical Mechanics
Abstract

Thermoelectric materials exhibit correlated transport of charge and heat. The Johnson-Nyquist noise formula $ 4 k_B T R $ for spectral density of voltage fluctuations accounts for fluctuations associated solely with Ohmic dissipation. Applying the fluctuation-dissipation theorem, we generalize the Johnson-Nyquist formula for thermoelectrics, finding an enhanced voltage fluctuation spectral density $4 k_B T R (1 + ZT)$ at frequencies below a thermal cut-off frequency $f_T$, where $ZT$ is the dimensionless thermoelectric material figure of merit. The origin of the enhancement in voltage noise is thermoelectric coupling of temperature fluctuations. We use a wideband ($f_T\sim1$ kHz), integrated thermoelectric micro-device to experimentally confirm our findings. Measuring the $ZT$ enhanced voltage noise, we experimentally resolve temperature fluctuations with an amplitude of $0.8~\mu \mathrm{K} \mathrm{Hz}^{-1/2}$ at a mean temperature of 295 K. We find that thermoelectric devices can be used for thermometry with sufficient resolution to measure the fundamental temperature fluctuations described by the fluctuation-dissipation theorem.

Published
2022
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7. Intra-wire coupling in segmented Ni/Cu nanowires deposited by electrodeposition

Author

Sergelius, Philip, Lee, Ji, Fruchart, Olivier, Salem, Mohamed, Allende, Sebastian, Escobar, Robert, Gooth, Johannes, Zierold, Robert, Toussaint, Jean-Christophe, Schneider, Sebastian, Pohl, Darius, Rellinghaus, Bernd, Martin, Sylvain, Garcia, Javier, Reith, Heiko, Spende, Anne, Toimil-Molares, Maria, Altbir, Dora, Cowburn, Russel, Görlitz, Detlef, and Nielsch, Kornelius

Subjects
Condensed Matter - Materials Science
Abstract

Segmented magnetic nanowires are a promising route for the development of three dimensional data storage techniques. Such devices require a control of the coercive field and the coupling mechanisms between individual magnetic elements. In our study, we investigate electrodeposited nanomagnets within host templates using vibrating sample magnetometry and observe a strong dependence between nanowire length and coercive field (25 nm to 5 $\mu$m) and diameter (25 nm to 45 nm). A transition from a magnetization reversal through coherent rotation to domain wall propagation is observed at an aspect ratio of approximately 2. Our results are further reinforced via micromagnetic simulations and angle dependent hysteresis loops. The found behavior is exploited to create nanowires consisting of a fixed and a free segment in a spin-valve like structure. The wires are released from the membrane and electrically contacted, displaying a giant magnetoresistance effect that is attributed to individual switching of the coupled nanomagnets. We develop a simple analytical model to describe the observed switching phenomena and to predict stable and unstable regimes in coupled nanomagnets of certain geometries.

Published
2016
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15. Integration of Multifunctional Epitaxial (Magnetic) Shape Memory Films in Silicon Microtechnology.

Author

Fink, Lukas, Kar, Satyakam, Lünser, Klara, Nielsch, Kornelius, Reith, Heiko, and Fähler, Sebastian

Subjects
SHAPE memory alloys, SILICON films, HEUSLER alloys, EPITAXY, MICROTECHNOLOGY, ENERGY harvesting, DENTAL metallurgy
Abstract

Magnetic shape memory alloys exhibit various multifunctional properties, which range from high stroke actuation and magnetocaloric refrigeration to thermomagnetic energy harvesting. Most of these applications benefit from miniaturization and a single crystalline state. Epitaxial film growth is so far only possible on some oxidic substrates, but they are expensive and incompatible with standard microsystem technologies. Here, epitaxial growth of Ni–Mn–based Heusler alloys with single crystal‐like properties on silicon substrates is demonstrated by using a SrTiO3 buffer. It is shown that this allows using standard microfabrication technologies to prepare partly freestanding patterns. This approach is versatile, as its applicability for the NiTi shape memory alloy is demonstrated and spintronic and thermoelectric Heusler alloys are discussed. This paves the way for integrating additional multifunctional effects into state‐of‐the‐art microelectronic and micromechanical technology, which is based on silicon. [ABSTRACT FROM AUTHOR]

Published
2023
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17. Exchange Bias Effect of Ni@(NiO,Ni(OH)2) Core/Shell Nanowires Synthesized by Electrochemical Deposition in Nanoporous Alumina Membranes

Author

García, Javier, primary, Gutiérrez, Ruth, additional, González, Ana S., additional, Jiménez-Ramirez, Ana I., additional, Álvarez, Yolanda, additional, Vega, Víctor, additional, Reith, Heiko, additional, Leistner, Karin, additional, Luna, Carlos, additional, Nielsch, Kornelius, additional, and Prida, Víctor M., additional

Published
2023
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23. Doped Organic Micro-Thermoelectric Coolers with Rapid Response Time

Author

Wang, Shu-Jen, Wohlrab, Steve, Reith, Heiko, Berger, Dietmar, Kleemann, Hans, Nielsch, Kornelius, Leo, Karl, Wang, Shu-Jen, Wohlrab, Steve, Reith, Heiko, Berger, Dietmar, Kleemann, Hans, Nielsch, Kornelius, and Leo, Karl

Abstract

Local thermal management has important implications regarding comfort, energy consumption, and electronic device performance/lifetime. While organic thermoelectrics have emerged as promising materials for flexible thermoelectric energy harvesting devices, their potential as Peltier cooling element has been largely overlooked. Here, micro-thermoelectric coolers based on doped small molecule thin-films with a fast response time (around 25 µs) which is among the fastest micro-thermoelectric coolers reported are presented. This experimental cooling performance is supported by simulation using the finite-element method for thermal transport. The results show that organic thermoelectrics offer great potential for flexible and wearable micro-thermoelectric cooling applications.

Published
2022

24. Exchange Bias Effect of Ni@(NiO,Ni(OH) 2) Core/Shell Nanowires Synthesized by Electrochemical Deposition in Nanoporous Alumina Membranes.

Author

García, Javier, Gutiérrez, Ruth, González, Ana S., Jiménez-Ramirez, Ana I., Álvarez, Yolanda, Vega, Víctor, Reith, Heiko, Leistner, Karin, Luna, Carlos, Nielsch, Kornelius, and Prida, Víctor M.

Subjects
NANOWIRES, SEMICONDUCTOR technology, EXCHANGE bias, MAGNETIC fields, MAGNETIC properties, MAGNETIC control, ALUMINUM oxide
Abstract

Tuning and controlling the magnetic properties of nanomaterials is crucial to implement new and reliable technologies based on magnetic hyperthermia, spintronics, or sensors, among others. Despite variations in the alloy composition as well as the realization of several post material fabrication treatments, magnetic heterostructures as ferromagnetic/antiferromagnetic coupled layers have been widely used to modify or generate unidirectional magnetic anisotropies. In this work, a pure electrochemical approach has been used to fabricate core (FM)/shell (AFM) Ni@(NiO,Ni(OH)2) nanowire arrays, avoiding thermal oxidation procedures incompatible with integrative semiconductor technologies. Besides the morphology and compositional characterization of these core/shell nanowires, their peculiar magnetic properties have been studied by temperature dependent (isothermal) hysteresis loops, thermomagnetic curves and FORC analysis, revealing the existence of two different effects derived from Ni nanowires' surface oxidation over the magnetic performance of the array. First of all, a magnetic hardening of the nanowires along the parallel direction of the applied magnetic field with respect their long axis (easy magnetization axis) has been found. The increase in coercivity, as an effect of surface oxidation, has been observed to be around 17% (43%) at 300 K (50 K). On the other hand, an increasing exchange bias effect on decreasing temperature has been encountered when field cooling (3T) the oxidized Ni@(NiO,Ni(OH)2) nanowires below 100 K along their parallel lengths. [ABSTRACT FROM AUTHOR]

Published
2023
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28. Terahertz conductivity of nanograined bulk Bi2Te3

Author

Han, Jeong Woo, primary, Izadi, Sepideh, additional, Salloum, Sarah, additional, Wolff, Ulrike, additional, Schnatmann, Lauritz, additional, Bhattacharya, Ahana, additional, Asaithambi, Aswin, additional, Matschy, Sebastian, additional, Schlörb, Heike, additional, Reith, Heiko, additional, Perez, Nicolas, additional, Nielsch, Kornelius, additional, Schulz, Stephan, additional, Schierning, Gabi, additional, and Mittendorff, Martin, additional

Published
2022
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33. Interface‐Dominated Topological Transport in Nanograined Bulk Bi 2 Te 3

Author

Izadi, Sepideh, primary, Han, Jeong Woo, additional, Salloum, Sarah, additional, Wolff, Ulrike, additional, Schnatmann, Lauritz, additional, Asaithambi, Aswin, additional, Matschy, Sebastian, additional, Schlörb, Heike, additional, Reith, Heiko, additional, Perez, Nicolas, additional, Nielsch, Kornelius, additional, Schulz, Stephan, additional, Mittendorff, Martin, additional, and Schierning, Gabi, additional

Published
2021
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36. Crystal Structure Analysis and Magneto-Transport Investigation of Co1-xFexSi (with x=0% to x=20%)

Author

Schnatmann, Lauritz, Lammel, Michaela, Damm, Christine, Levin, Aleksandr A., Perez, Nicolas, Novikov, Sergey, Burkov, Alexander, Reith, Heiko, Nielsch, Kornelius, and Schierning, Gabi

Subjects
charge density wave, chiral anomaly, cobalt silicide, quantum transport
Abstract

Cobalt monosilicide, CoSi, belongs to the new class of materials, featuring Weyl nodes in the bulk band structure, located very close to the Fermi energy. By shifting the chemical potential into these Weyl nodes using Fe-doping, quantum effects like the chiral anomaly and weak anti localization have been evidenced. However, the behavior of these effects with respect to the doping concentration is largely unexplored. Crystal structure and the electrical transport properties in single crystalline CoSi micro-ribbons with different Fe-doping are studied to identify the characteristic temperatures of electronic quantum and correlation effects. For the crystal structure analysis, transmission electron microscopy and powder X-ray diffraction analysis with a refined structural model is performed based on Le Bail fitting to analyze the lattice parameter. Hereby, the change of the lattice parameter of Co1-xFexSi is shown with increasing Fe content. In the electrical transport analysis, the occurrence of chiral anomaly and the weak anti localization effect in Fe-doped CoSi are presented. It is shown that these effect can be tailored by Fe-doping in CoSi.

Published
2021

37. Influence of Nanoparticle Processing on the Thermoelectric Properties of (BiₓSb₁−X)₂Te₃ Ternary Alloys

Author

Salloum, Sarah, Bendt, Georg, Heidelmann, Markus, Loza, Kateryna, Bayesteh, Samaneh, Sepideh Izadi, M., Kawulok, Patrick, He, Ran, Schlörb, Heike, Perez, Nicolas, Reith, Heiko, Nielsch, Kornelius, Schierning, Gabi, and Schulz, Stephan

Subjects
Chemie
Abstract

The synthesis of phase-pure ternary solutions of tetradymite-type materials (BiₓSb₁−ₓ)₂Te₃ (x=0.25; 0.50; 0.75) in an ionic liquid approach has been carried out. The nanoparticles are characterized by means of energy-dispersive X-ray spectroscopy (EDX), powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), and transmission electron microscopy. In addition, the role of different processing approaches on the thermoelectric properties - Seebeck coefficient as well as electrical and thermal conductivity - is demonstrated. CA Schulz und CA extern (Schierning)

Published
2021

41. Influence of Nanoparticle Processing on the Thermoelectric Properties of (Bi x Sb 1−X ) 2 Te 3 Ternary Alloys

Author

Salloum, Sarah, primary, Bendt, Georg, additional, Heidelmann, Markus, additional, Loza, Kateryna, additional, Bayesteh, Samaneh, additional, Sepideh Izadi, M., additional, Kawulok, Patrick, additional, He, Ran, additional, Schlörb, Heike, additional, Perez, Nicolas, additional, Reith, Heiko, additional, Nielsch, Kornelius, additional, Schierning, Gabi, additional, and Schulz, Stephan, additional

Published
2021
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44. Study of the Annealing Effects of Sputtered Bi2Te3 Thin Films with Full Thermoelectric Figure of Merit Characterization.

Author

Naumochkin, Maksim, Park, Gyu-Hyeon, Nielsch, Kornelius, and Reith, Heiko

Subjects
THIN films, CHARGE carrier mobility, POINT defects, ENERGY harvesting, HIGH temperatures, THERMOELECTRIC power
Abstract

Micro‐thermoelectric (TE) devices have a great potential for future applications in the field of energy harvesting to power autonomous sensors. Bi2Te3 sputtered at elevated substrate temperatures exhibits a high figure of merit (ZT) suitable for the fabrication of micro‐TE devices. However, a lift‐off process that does not allow higher substrate temperatures is often used, and although Bi2Te3 is a well‐studied TE material, it lacks full ZT characterization of thin films. Herein, the full TE characterization of sputtered Bi2Te3 thin films is presented, including the charge carrier concentration and mobility, which are deposited at room temperature and postannealed between 150 and 300 °C. The influence of the annealing time and temperature is investigated on a 90 nm‐thick Bi2Te3 film. A maximum ZT of 0.20 is found, which results from the increasing crystallinity and reduction of point defects. To investigate the thickness dependency, Bi2Te3 films with thicknesses of 90, 170, 350, and 470 nm are annealed at 250 °C. A maximum ZT value of 0.26 is observed for the 350 nm Bi2Te3 film. Furthermore, it can be shown that with increasing film thickness, the annealing time has to be increased to maximize ZT. [ABSTRACT FROM AUTHOR]

Published
2022
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45. Crystal Structure Analysis and Magneto‐Transport Investigation of Co1−xFexSi (with x = 0% to x = 20%).

Author

Schnatmann, Lauritz, Lammel, Michaela, Damm, Christine, Levin, Aleksandr A., Pérez, Nicolas, Novikov, Sergey, Burkov, Alexander, Reith, Heiko, Nielsch, Kornelius, and Schierning, Gabi

Subjects
CRYSTAL structure, X-ray powder diffraction, LATTICE constants, FERMI energy, TRANSMISSION electron microscopy, COBALT
Abstract

Cobalt monosilicide, CoSi, belongs to the new class of materials, featuring Weyl nodes in the bulk band structure, located very close to the Fermi energy. By shifting the chemical potential into these Weyl nodes using Fe‐doping, quantum effects like the chiral anomaly and weak anti localization have been evidenced. However, the behavior of these effects with respect to the doping concentration is largely unexplored. Crystal structure and the electrical transport properties in single crystalline CoSi micro‐ribbons with different Fe‐doping are studied to identify the characteristic temperatures of electronic quantum and correlation effects. For the crystal structure analysis, transmission electron microscopy and powder X‐ray diffraction analysis with a refined structural model is performed based on Le Bail fitting to analyze the lattice parameter. Hereby, the change of the lattice parameter of Co1−xFexSi is shown with increasing Fe content. In the electrical transport analysis, the occurrence of chiral anomaly and the weak anti localization effect in Fe‐doped CoSi are presented. It is shown that these effect can be tailored by Fe‐doping in CoSi. [ABSTRACT FROM AUTHOR]

Published
2022
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46. Electrochemical Deposition: Thermoelectric Characterization Platform for Electrochemically Deposited Materials (Adv. Electron. Mater. 4/2020)

Author

Barati, Vida, primary, Garcia Fernandez, Javier, additional, Geishendorf, Kevin, additional, Schnatmann, Lauritz Ule, additional, Lammel, Michaela, additional, Kunzmann, Alexander, additional, Pérez, Nicolás, additional, Li, Guodong, additional, Schierning, Gabi, additional, Nielsch, Kornelius, additional, and Reith, Heiko, additional

Published
2020
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48. Topological Electronics: Signatures of a Charge Density Wave Phase and the Chiral Anomaly in the Fermionic Material Cobalt Monosilicide CoSi (Adv. Electron. Mater. 2/2020)

Author

Schnatmann, Lauritz, primary, Geishendorf, Kevin, additional, Lammel, Michaela, additional, Damm, Christine, additional, Novikov, Sergey, additional, Thomas, Andy, additional, Burkov, Alexander, additional, Reith, Heiko, additional, Nielsch, Kornelius, additional, and Schierning, Gabi, additional

Published
2020
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49. Doping High‐Mobility Donor–Acceptor Copolymer Semiconductors with an Organic Salt for High‐Performance Thermoelectric Materials

Author

Guo, Jing, primary, Li, Guodong, additional, Reith, Heiko, additional, Jiang, Lang, additional, Wang, Ming, additional, Li, Yuhao, additional, Wang, Xinhao, additional, Zeng, Zebing, additional, Zhao, Huaizhou, additional, Lu, Xinhui, additional, Schierning, Gabi, additional, Nielsch, Kornelius, additional, Liao, Lei, additional, and Hu, Yuanyuan, additional

Published
2020
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50. Signatures of a Charge Density Wave Phase and the Chiral Anomaly in the Fermionic Material Cobalt Monosilicide CoSi

Author

Schnatmann, Lauritz, Geishendorf, Kevin, Lammel, Michaela, Damm, Christine, Novikov, Sergey, Thomas, Andy, Burkov, Alexander, Reith, Heiko, Nielsch, Kornelius, and Schierning, Gabi

Subjects
charge density wave, cobalt silicide, chiral anomalies, quantum transport, 621.3
Abstract

Materials with topological electronic states have emerged as one of the most exciting discoveries of condensed quantum matter, hosting quasiparticles with extremely low effective mass and high mobility. Weyl materials contain such topological states in the bulk and additionally have a non-trivial chiral charge. However, despite known quantum effects caused by these chiral states, the interplay between chiral states, and a charge density wave phase, an ordering of the electrons to a correlated phase is not experimentally explored. Indications for the formation of a charge density wave phase in the Weyl material cobalt monosilicide CoSi are observed. Furthermore, the typical signatures of the charge density wave phase together with typical signatures of Weyl fermions in magnetic field dependent electrical transport characterization are investigated. The charge density wave and the chiral contribution to the electrical magneto-transport are separated as well as a suppression of the charge density wave phase is observed in magnetic fields. �� 2019 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Published
2019
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