Journal of the Magnetics Society of Japan
Online ISSN : 1882-2932
Print ISSN : 1882-2924
ISSN-L : 1882-2924
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Power Magnetics
Magnetic Recoading
  • T. Shimizu, M. Ohtake, M. Futamoto, F. Kirino, N. Inaba
    2019 Volume 43 Issue 6 Pages 109-113
    Published: November 01, 2019
    Released: November 01, 2019
    [Advance publication] Released: October 19, 2019
    JOURNALS OPEN ACCESS

      10-nm-thick FePt alloy films without and with MgO, VC, and VN cap-layers of 2 nm thickness are prepared on MgO, VC, and VN single-crystal underlayers of (001) orientation by using a two-step method consisting of low-temperature deposition at 200 °C followed by high-temperature annealing at 600 °C. The surface energies of MgO and vanadium compounds (VC, VN) are respectively lower and higher than that of FePt alloy. The influences of combination of underlayer and cap-layer materials on the surface flatness, the lattice deformation, the degree of L10 ordering, and the magnetic anisotropy are investigated. FePt(001) single-crystal films without and with MgO, VC, and VN(001) single-crystal cap-layers grow epitaxially on all the underlayers. The in-plane lattice of FePt film is expanded in accommodation of lattice mismatch with underlayer and/or cap-layer. The lattice deformation aligns the c-axis perpendicular to the substrate surface and enhances L10 ordering. A higher order degree and a stronger perpendicular magnetic anisotropy are obtained by using a combination of VN underlayer and MgO cap-layer. The present study shows that employment of underlayer and cap-layer materials whose surface energies are respectively higher and lower than that of FePt alloy is effective in enhancing order degree and magnetic anisotropy.

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  • T. Kobayashi, Y. Nakatani, Y. Fujiwara
    2019 Volume 43 Issue 6 Pages 114-119
    Published: November 01, 2019
    Released: November 01, 2019
    [Advance publication] Released: October 19, 2019
    JOURNALS OPEN ACCESS

      The thermal stability factor KumVm /kT and the anisotropy constant ratio Ku /Kbulk necessary for 10 years of archiving in heat-assisted magnetic recording of 2 Tbpsi are evaluated by employing a bit error rate calculation using a grain error probability P. Although the attempt frequency f0 in P is a function of the Gilbert damping constant, the Curie temperature, Ku /Kbulk , the grain volume, and temperature, f0 can be treated as a constant. The Gilbert damping constant and the Curie temperature variation are parameters with little impact. On the other hand, the grain size variation, the grain number per bit n, the mean Curie temperature Tcm , and the storage temperature T are parameters with a strong impact on bit error rate. Although KumVm /kT decreases as n increases due to a statistical problem, a larger Ku /Kbulk is necessary as n increases due to a smaller grain size. A larger Ku /Kbulk is also necessary as Tcm decreases. The bit error rate increases rapidly as T increases.

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Spin Electronics
  • Y. Takamura, Y. Stutler, E. Matsushita, K. Shinohara, T. Suzuki, S. Na ...
    2019 Volume 43 Issue 6 Pages 120-124
    Published: November 01, 2019
    Released: November 01, 2019
    [Advance publication] Released: October 19, 2019
    JOURNALS OPEN ACCESS

      We systematically investigated perpendicular magnetic anisotropy (PMA) in bilayers comprising ultrathin full-Heusler Co2FeSi (CFS) alloy and MgO as an insulator. The MgO layer was fabricated using two different sputtering techniques: reactive sputtering and radio-frequency sputtering. The characteristics of the layers fabricated using the different methods were compared. Irrespective of the MgO fabrication technique, the CFS/MgO bilayers exhibited PMA when the CFS surface was exposed to oxygen, which resulted in additional Fe–O bonds at the interface. Additionally, we characterized PMA in the bilayers while varying the substrate temperature TS for CFS sputtering. CFS samples that were 0.6-nm thick exhibited PMA when they were formed at TS as high as 300°C. The bilayer formed at 350°C exhibited in-plane magnetic anisotropy. Quantitative analysis of the magnetic anisotropy energy density revealed that the dominant magnetic anisotropy contribution in PMA differed between the bilayers formed at 300°C and 350°C. We expect these findings to be useful in the further development of high spin-polarized ferromagnetic electrodes containing PMA for next-generation spintronics devices.

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Measurement Technique, High-Frequency Devices
  • S. Endo, M. Sato, Y. Bu, T. Mizuno
    2019 Volume 43 Issue 6 Pages 125-132
    Published: November 01, 2019
    Released: November 01, 2019
    [Advance publication] Released: October 19, 2019
    JOURNALS OPEN ACCESS

    To improve the fuel efficiency of electric vehicles, it is necessary to reduce the weight of the wireless power transfer coil in the vehicles. Resistance due to the skin effect or the proximity effect increases during wireless power transfer, decreasing the transmission efficiency. This study aims to reduce the weight of the coil by replacing it with an aluminum plate coil, which is easy to manufacture and inexpensive. The weight of the coil was reduced by 3/4 (from 1.9 to 0.44 kg) when compared with copper Litz wire. Furthermore, the AC resistance was reduced by applying magnetic coating to the same coil. Consequently, the transmission efficiency increased from 88.2% to 89.3%, an improvement of 1.1%. The optimal material for magnetic coating was revealed in an analysis.

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