Enhanced thermoelectric performance in spark plasma textured bulk n-type BiTe2.7Se0.3 and p-type Bi0.5Sb 1.5Te3

Bulk p and n-type bismuth tellurides were prepared using spark plasma texturization method. The texture development along the uniaxial load in the 001 direction is confirmed from both x-ray diffraction analysis and electron backscattering diffraction measurements. Interestingly, those textured samples outperform the samples prepared by conventional spark plasma sintering (SPS) leading to a reduced thermal conductivity in the ab-plane. The textured samples of n-type BiTe2.7Se0.3 and p-type Bi0.5Sb 1.5Te3 showed a 42% and 33% enhancement in figure of merit at room temperature, respectively, as compared to their SPS counterparts, opening the route for applications. © 2013 AIP Publishing LLC

High-throughput synthesis of functional oxide films

Epitaxy of metal oxides is of great interest since it provides a way to obtain desired novel properties for the applications such as electronics and energy. However, earlier epitaxy research's have been restricted because of the limited range of compositions and low-index of commercially available single crystal substrates. Consequently, novel epitaxy synthesis methods need to be developed in order to go beyond the present demands of of single crystal substrates in terms of phase, composition, size, orientation and symmetry. In this research work, we have developed a high-throughput synthesis process, called combinatorial substrate epitaxy (CSE), where an oxide film is grown epitaxially on a polycrystalline substrate. As a proof-of-concept, we firstly fabricated Ca3Co4O9 films on Al2O3 ceramics. Films have a good local epitaxial registry, and the Seebeck coefficient is about 170 µV/K at 300 K. High quality BiFeO3/La0.7Sr0.3MnO3 thin film heterostructures were secondly deposited on dense LaAlO3 ceramics prepared by spark plasma sintering. Piezoforce microscopy was used to confirm the local ferroelectric properties. Thirdly, we investigate the growth of of metastable monoclinic Dy2Ti2O7 epitaxial films on polycrystalline La2Ti2O7 substrates. We conclude that CSE approach opens the way towards unexpected electronic properties in oxide films

Enhanced thermoelectric performance in spark plasma textured bulk n -type BiTe 2.7 Se 0.3 and p-type Bi 0.5 Sb 1.5 Te 3

International audienceBulk p and n-type bismuth tellurides were prepared using spark plasma texturization method. The texture development along the uniaxial load in the 001 direction is confirmed from both x-ray diffraction analysis and electron backscattering diffraction measurements. Interestingly, those textured samples outperform the samples prepared by conventional spark plasma sintering (SPS) leading to a reduced thermal conductivity in the ab-plane. The textured samples of n-type BiTe2.7Se0.3 and p-type Bi0.5Sb1.5Te3 showed a 42% and 33% enhancement in figure of merit at room temperature, respectively, as compared to their SPS counterparts, opening the route for applications

Manipulation of Exchange Bias Effect via All-Solid-State Li-Ion Redox Capacitor with Antiferromagnetic Electrode

The electric field control of the exchange bias has considerable application scope in modern spintronic devices such as magnetic random-access memories. Herein, we utilize an all-solid-state Li-ion redox capacitor with an antiferromagnetic electrode for reversible control of the exchange bias in a Co/Co3O4 heterostructure. The controlled intercalation and deintercalation of Li ions in the antiferromagnetic Co3O4 anode via galvanostatic charge and discharge enables reversible and nonvolatile control of the exchange bias. The mechanism of exchange-bias control in the Co/Co3O4 heterostructure is studied using various characterization techniques. This work establishes an approach to control the exchange bias in all-solidstate magnetoionics, which is of great practical importance for the development of modern spintronic devices

Reversible Control of Magnetic Anisotropy and Magnetization in Amorphous Co40Fe40B20 Thin Films via All-Solid-State Li-ion Redox Capacitor

Reversible Control of Magnetic Anisotropy and Magnetization in Amorphous Co40Fe40B20 Thin Films via All-Solid-State Li-ion Redox Capacito

High-throughput investigation of orientations effect on nanoscale magnetization reversal in cobalt ferrite thin films induced by electric field

The magnetoelectric device concept which enables the non-volatile electric field control of magnetism needs to be investigated for the development of practical information storage devices. In this aspect, the emerging field of magneto-ionics based on the modulation of magnetism by field-driven ion migration is promising because it only requires a simple sample structure in the solid state and has good cyclability. However, the degree of ion migration within the magnetic structure is strongly dependent on the crystal orientations. Since the epitaxial films growing on the commercial single crystal substrates have limited orientations, the ability of magnetism modulated by field-driven ion migration cannot be optimized and understood by using these data. In this work, we utilized the high-throughput synthesis approach, namely, combinatorial substrate epitaxy, which utilizes a polycrystalline substrate. This provides a platform to develop and understand the degree of ionic migration in different orientations of the model system CoFe2O4 (CFO) films. The library of electric driven nanoscale magnetization reversal data of CFO with different orientations was obtained by applying the electric field in the same region of known CFO grain orientations. It was determined from the analysis that the [110] crystal direction exhibits the maximum nanoscale magnetization reversal ratio. This is mainly attributed to the ease Co2+ migration in the [110] direction under the electric field assisted by a Fe3+ and oxygen vacancies. (C) 2017 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/)

Reversibly controlled magnetic domains of Co film via electric field driven oxygen migration at nanoscale

Electric field control of perpendicular magnetic anisotropy (PMA) can enable low power consumption for perpendicular magnetic random access memory devices. However, the tuning of PMA by the electric field in ferromagnetic metal thin films is less efficient and limited to the interface due to the screening effect. Alternatively, the magnetoionic effect can control PMA efficiently, which utilizes ion migrations over the surface of the ferromagnetic metal by interfacing it with the charge reservoir of oxygen ions like GdOx. In this paper, we report the reversibly controlled magnetic domains of PMA Co in the Pt/Co/GdOx trilayer via the electric field at the nanoscale using conductive atomic force microscopy and magnetic force microscopy (MFM). The magnetic domain phase values determined by MFM decrease and increase when negative and positive bias voltages of magnitude 4V are applied to the surface of GdOx, respectively. These results suggest a path toward control of PMA materials at the nanoscale by the electric field for information storage devices.National Key R&D Program of China [2016YFA0201102]; National Natural Science Foundation of China [51871232, 51571208, 51525103, 6171101158]; Key Research Program of the Chinese Academy of Sciences [KJZD-EW-M05]; Ningbo Science and Technology Bureau (2025 ST Megaprojects); Ningbo Science and Technology Innovation Team [2015B11001]; Youth Innovation Promotion Association of the Chinese Academy [2016270]12 month embargo; published online: 10 June 2019This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Spin-valve-like magnetoresistance in a Ni-Mn-In thin film

Spin valve devices, the resistive state of which is controlled by switching the magnetization of a free ferromagnetic layer with respect to a pinned ferromagnetic layer, rely on the scattering of electrons within the active medium to work. Here we demonstrate spin-valve-like effect in the Ni-Mn-In thin films, which consists of a ferromagnetic phase embedded in an antiferromagnetic matrix. Through transport and magnetic measurements, we confirm that scattering at the interfaces between the two phases gives rise to a unidirectional anisotropy and the spin-valve-like effect in this system. The magnitude of the spin-valve-like magnetoresistance (about 0.4% at 10 K) is stable within the temperature range of 10-400 K. The low- and high-resistance states cannot be destroyed even under a high magnetic field of 100 k Omega e. This finding opens up a way of realizing the spin valve effect in materials with competing ferromagnetic and antiferromagnetic interactions, where the interface between these phases acts as the active medium

2D Magnetic Mesocrystals for Bit Patterned Media

Bit patterned media exhibits great potential in satisfying the increasing demand for higher information storage density, but the present media fabrication technique is complicated. Here, a 2D magnetic mesocrystal with monodisperse CoFe2O4 (CFO) nanocrystals is fabricated through a combination of nanoseeds layer growth and oxides self-assembly method. The monodisperse CFO nanomagnets protrude from the substrate surface with perfect crystal facets, specific crystallographic orientation, and are fully relaxed. Systematic magnetic characterizations, such as dynamic cantilever magnetometry for single CFO nanocrystal, magnetic force microscopy, and superconducting quantum interference device magnetometry for large area, reveal the novel tilted magnetic anisotropy and the switchable single domain state. This work provides a new way to fabricate bit patterned media with controlled material structure simply by a nanoseeds-mediated self-assembly method

Enhanced thermoelectric performance in spark plasma textured bulk n -type BiTe 2.7 Se 0.3 and p-type Bi 0.5 Sb 1.5 Te 3

International audienc