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Fukuhara M.,Tohoku University | Fukuhara M.,Research Institute for Electromagnetic Materials | Yoshida H.,Tohoku University | Yoshida H.,Research Institute for Electromagnetic Materials
Journal of Alloys and Compounds | Year: 2014

In anticipation of prompt ac charging/discharging characteristics, the capacitance of de-alloyed Si1-x(Al0.5,V 0.5)x (x = 0.15, 0.2, 0.3, and 0.4) alloy ribbons with resistivities of 0.01-4300 Ωcm was measured as a function of frequency between 1 mHz and 1 MHz, using exponential transient analysis for electric charging/discharging. The capacitance of de-alloyed Si-7.5 at.%.Al-7.5 at.%. V obtained by prompt (100 ms-25 ns) charging/discharging decreased logarithmically from 105 μF to 18 pF as frequency increased from 1 mHz to 10 kHz, and then saturated between 10 kHz and 1 MHz. From the observed electrode distance dependence on capacitance, we deduced that the alloy consisted of a distributed constant equivalent circuit (series with 1.2% parallel), analogous to electric double layer capacitors. © 2012 Elsevier B.V. All rights reserved.

Kobayashi N.,Research Institute for Electromagnetic Materials | Masumoto H.,Tohoku University | Takahashi S.,Tohoku University | Maekawa S.,Japan Atomic Energy Agency
Nature Communications | Year: 2014

The electric and magnetic properties of matter are of great interest for materials science and their use in electronic applications. Large dielectric and magnetoelectric responses of materials at room temperature are a great advantage for electromagnetic device applications. Here we present a study of FeCo-MgF nanogranular films exhibiting giant dielectric and magnetoelectric responses at room temperature; with dielectric constant ε′ = 490 and magnetoelectric response Δε′/ε′0 = 3%. In these films, Fe-Co alloy-based nanometer-sized magnetic granules are dispersed in a Mg-fluoride-based insulator matrix. Insulating nanogranular films are a new class of multifunctional materials. The giant responses are caused by spin-dependent charge oscillation between magnetic granules via quantum-mechanical tunnelling. A possible application of such insulating nanogranular materials with giant response is in the construction of a tunable device, in which impedance components such as capacitance and inductance are tunable at room temperature. © 2014 Macmillan Publishers Limited. All rights reserved.

Kijima H.,Tohoku University | Ohnuma S.,Tohoku University | Ohnuma S.,Research Institute for Electromagnetic Materials | Masumoto H.,Tohoku University
IEEE Transactions on Magnetics | Year: 2011

Co-Al-N films with wide Co compositional range were prepared by the rf-sputtering method in order to obtain soft magnetic properties at high frequencies. The films consisted of Co nano-granules 3-5 nm in diameter, randomly dispersed in an AlN amorphous matrix. Ferromagnetic properties were obtained in the film with a Co content of 47-80 at.%. The films were shown perpendicular magnetic anisotropy with coercivity around 20-50 Oe, and had the same magnetization curve in all film plane directions. Co-Al-N films showed an excellent frequency response of permeability. The permeability (μ) of Co 80Al14N6 film, in particular, was constant up to 1 GHz, and exhibited a clear peak at the resonance frequency (fr) at around 1.2 GHz. The origin of this specific μ -f response of isotropic Co-Al-N films with perpendicular magnetic anisotropy can be attributed to the rotatable magnetic anisotropy. © 2011 IEEE.

Fukuhara M.,Tohoku University | Fukuhara M.,Waseda University | Sugawara K.,Research Institute for Electromagnetic Materials
Thin Solid Films | Year: 2015

Amorphous titanium oxide film on Ti–Ni–Si amorphous alloy ribbons was prepared by anodic polarization process in ten kinds of electrolyte solutions. Addition of NH4F in (NH4)2SO4 solution accelerates an increase in current, i.e. formation of soluble Ti-fluoride complexes, resulting in the amorphous titanium oxide layers with nanometer-sized pores. Pore size decreases down to 12 nm with decreasing of applied voltage from 30 to 5 V. However, parallel capacitance Cp, series capacitance Cs, and RCs constant increase with decrease of pore size from 23 to 18 nm and then decrease in pore size region from 18 to 12 nm by formation of penetrating tunnels in the layer. It needs further enhancement of RCs for realization of superior electric storage capacitor. © 2015 Elsevier B.V.

Abe S.,Research Institute for Electromagnetic Materials
Materials for Renewable and Sustainable Energy | Year: 2015

This study investigates one-step synthesis of composite thin film with ZnSe and PbTeSe ternary solid solution using hot-wall deposition (HWD) with multiple resources of PbTe and ZnSe. HWD consists of three electric furnaces, designated as wall, source-1, and source-2. The PbTe and ZnSe sources were located in the source-2 and source-1 furnaces for simultaneous evaporation to a glass substrate (Corning Eagle 2000). The substrate temperature was changed by circulating water controlled at temperatures of 340-274 K. X-ray diffraction indicates that composite thin films contain ZnSe with zinc-blende structure and PbTeSe ternary solid solution with NaCl structure. The Raman spectrum also suggests formation of ZnSe without alloying with Pb or Te. The lattice constant of the ternary solid solution gradually increases with increasing source temperature of PbTe. High-resolution transmission electron microscopy indicates that the ternary solid solution forms isolated nanocrystals of 16-30 nm in the composite thin film. Therefore, composite thin films are composed of PbTeSe ternary solid solution nanocrystals embedded in a ZnSe matrix. © 2015 The Author(s).

Abe S.,Research Institute for Electromagnetic Materials | Watanabe M.,Research Institute for Electromagnetic Materials
Materials Research Express | Year: 2014

This paper proposes a simple technique for preparing maghemite (Fe2O3) thin film using RF sputtering without a heating substrate, an oxygen atmosphere, or postannealing. Thin film was prepared using a composite target of Mg chips set on ceramic hematite (Fe2O3) in a pure Ar atmosphere on a water-cooled substrate. The results indicated that adding Mg to hematite produces polycrystalline maghemite. In addition, x-ray photo-electron spectroscopy indicated that adding Mg forms a metallic state. Therefore, the film contains a phase mixture of maghemite and metallic Mg. © 2014 IOP Publishing Ltd.

Watanabe M.,Research Institute for Electromagnetic Materials | Abe S.,Research Institute for Electromagnetic Materials
Journal of Nanoscience and Nanotechnology | Year: 2016

Fe3O4 has been known to have attractive physical properties for spintronic applications such as half-metallicity, however, its complicated magnetism has yet to be elucidated fully. We investigated the sputtered polycrystalline Fe3O4 thin film in which Ge was added for stabilization of the spinal structure. From X-ray photoelectron and Raman spectroscopies, major part of added Ge is found to be quadrivalent and considered to be incorporated in the spinel structure. Out-of-plane alignment of the local moment was confirmed by conversion electron Mössbauer spectroscopy and magnetization measurements with an applied field up to 70 kOe also support it. The Pawley refinement of the X-ray diffraction profile with a series of possible space groups in the spinel structure suggests that the crystal symmetry is reduced from cubic to tetragonal or orthorhombic spinels with (100) or (010) strains up to -0.231%. The uniaxial anisotropy constants Ku for the tetragonally distorted cases estimated from the evaluated strains and the ab-initio calculation were found to be around 1.05×106 erg/cm3. We consider that the magnetic anisotropy induced by the lattice distortion contributes to the out-of-plane alignment of local moments in addition to the previously reported effect by the exchange coupling across crystallographic defects of the antiphase boundaries. Copyright © 2016 American Scientific Publishers. All rights reserved.

Kuroki Y.,Toyota Motor Corporation | Kosaka Y.,Toyota Motor Corporation | Takahashi T.,Toyota Motor Corporation | Niwa E.,Research Institute for Electromagnetic Materials | And 2 more authors.
Proceedings - IEEE International Conference on Robotics and Automation | Year: 2013

This paper proposes a new torque sensing method, Cr-N alloy strain sensitive thin-film based torque sensors and distributed joint torque servo systems that enable human support robots to have capabilities to make physical interaction in adaptive and safe operation tasks. Stiffer torque sensing with stable and high-resolution sensing to meet practical level of the developed torque sensors have been achieved. We have developed the joint torque control based 4-DOF arm models in order to verify practical effectiveness of the proposed joint torque servo systems. We also demonstrated the joint torque control based bilateral master slave system exploring future applications. © 2013 IEEE.

Abe S.,Research Institute for Electromagnetic Materials
Nanoscale Research Letters | Year: 2013

This study investigates the preparation of InSb-added TiO2 nanocomposite films by RF sputtering. The optical absorption spectra are obviously shifted to visible and near-infrared regions. High-resolution transmission electron microscopy indicates that sphere-shaped InSb nanocrystals with a size of about 15 nm are dispersed in a matrix. The X-ray diffraction result reveals that the matrix forms a phase mixture of TiO2 and In2O3, which is also produced by decomposing the InSb during postannealing at 723 K. Therefore, the absorption shift is clearly due to quantum size effects of the InSb nanocrystals embedded in the wide-gap oxides TiO2 and In2O3. © 2013 Abe.

Abe S.,Research Institute for Electromagnetic Materials
Nanoscale Research Letters | Year: 2012

This paper investigates the crystal structure and optical absorption of Ge-doped Nb-oxide (Nb-Ge-O) thin films prepared by RF sputtering. A wide-gap material, Nb2O5, is selectively produced as a matrix to disperse Ge nanocrystals through compositional optimization with Ge chip numbers and oxygen ratio in argon. The optical-absorption spectra are obviously shifted to visible (vis) and near-infrared (NIR) regions, suggesting that a composite thin film with Ge nanocrystals dispersed in Nb2O5 matrix exhibits quantum-size effects. Accordingly, the two valuable characteristics of the Nb2O5 matrix and the vis-NIR absorption are found to be retained simultaneously in Nb-Ge-O thin films. © 2012 Abe.

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