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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). Source


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

The effect of Co content on the magnetic properties has been systematically investigated, to obtain high frequency soft magnetic Cox-(TiN) 1-x films. The films with Co content more than 73 at.% are perpendicular magnetic, and the films with Co content less than 45 at.% are both soft and super-para magnetic. In a wide-range of Co content (x=45-73 at.%), the Cox-(TiN)1-x nanogranular films show good soft magnetic properties, with coercivity as low as 4 Oe and magnetization around 6-12 kG. The permeability of the films is as high as about 400 and the resonance frequency is around 1 GHz. The films exhibit good thermal stability with the low coercivity of about 5 Oe even after the annealing at 500 ° C, which is very important in viewpoint of application like a CMOS-compatible fabrication technology. © 2011 IEEE. Source


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. Source


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. Source


Fukuhara M.,Tohoku University | Fukuhara M.,Research Institute for Electromagnetic Materials | Gangli C.,University of Tokyo | Matsubayashi K.,University of Tokyo | Uwatoko Y.,University of Tokyo
Applied Physics Letters | Year: 2012

Measurements under hydrostatic pressure of the electrical resistivity of (Ni 0.36Nb 0.24Zr 0.40) 100-xH x (x = 9.8, 11.5, and 14) glassy alloys have been made in the range of 0-8 GPa and 0.5-300 K. The resistivity of the (Ni 0.36Nb 0.24Zr 0.40) 86H 14 alloy changed its sign from negative to positive under application of 2-8 GPa in the temperature range of 300-22 K, coming from electron-phonon interaction in the cluster structure under pressure, accompanied by deformation of the clusters. In temperature region below 22 K, the resistivity showed negative thermal coefficient resistance by Debye-Waller factor contribution, and superconductivity was observed at 1.5 K. © 2012 American Institute of Physics. Source

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