Journal of the Magnetics Society of Japan
Online ISSN : 1882-2932
Print ISSN : 1882-2924
ISSN-L : 1882-2924
Volume 44 , Issue 3
Showing 1-6 articles out of 6 articles from the selected issue
Power Magnetics
  • A. Yao, R. Moriyama, T. Hatakeyama
    2020 Volume 44 Issue 3 Pages 52-55
    Published: May 01, 2020
    Released: May 01, 2020
    [Advance publication] Released: February 21, 2020
    JOURNAL OPEN ACCESS

      This paper discusses the iron loss and magnetic hysteresis properties of a ring core of nanocrystalline magnetic materials (NMM) at room temperature (RT) and high temperature (HT) under pulse-width-modulation (PWM) inverter excitation. As in the case of the DC hysteresis loop, the coercivity of the NMM ring core at 300C (HT) under PWM inverter excitation is larger than that at RT, mainly because of weakening of intergranular magnetic coupling at HT. In addition, in the NMM ring core, the area of the minor loops at HT increases compared with that at RT. Iron loss in the NMM core fed by the PWM inverter increases in tandem with an increase in temperature. Hysteresis loss increases dramatically in tandem with an increase in temperature for every tested case. In a low carrier frequency region, the eddy current loss at 300C increases.

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Spin Electronics
  • M. Ishikawa, Y. Saito, K. Hamaya
    2020 Volume 44 Issue 3 Pages 56-63
    Published: May 01, 2020
    Released: May 01, 2020
    [Advance publication] Released: April 09, 2020
    JOURNAL OPEN ACCESS

      In this paper, we introduce the current status of research and development on silicon-based spin metal-oxide-semiconductor field-effect transistors (Si spin-MOSFETs) in terms of electrical spin injection, spin transport, and spin detection in Si-based lateral spin-valve devices. First, it is important for understanding the spin transport in Si to obtain reliably large spin signals for analyses. By using n+-Si spin-transport layers with a small cross-sectional area of ~0.3 μm2, we can observe 50-fold the magnitude of four-terminal nonlocal (NL) magnetoresistance signals and NL Hanle signals at room temperature in previous works. Next, by analyzing these spin signals, we can reliably estimate the spin diffusion length and spin relaxation time of n+-Si at room temperature. Also, we clarify that inter-valley spin-flip scattering is one of the dominant spin relaxation mechanisms in n+-Si at room temperature. Furthermore, we find the crystal orientation effect on spin injection/detection efficiency in n+-Si and discuss the possible origins. Finally, we demonstrate a room-temperature MR ratio of 0.06%, twice as large as that in the previous work.

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Hard and Soft Magnetic Materials
  • R. Matsunami, M. Matsuura, N. Tezuka, S. Sugimoto
    2020 Volume 44 Issue 3 Pages 64-69
    Published: May 01, 2020
    Released: May 01, 2020
    [Advance publication] Released: April 09, 2020
    JOURNAL OPEN ACCESS

    In an effort to increase the maximum energy product ((BH)max) and coercivity (HcJ) of Zn-bonded Sm−Fe−N magnets, we developed a process for preparing Sm−Fe−N and Zn powders with low oxygen contents and subjected them to spark plasma sintering. The oxygen content, remanence, and coercivity of the Sm−Fe−N powder were 0.22 wt%, 151 A·m2·kg−1, and 0.72 MA·m−1, respectively. The oxygen content and secondary average particle size of the Zn powder were 0.083 wt% and 0.93 μm, respectively. The magnetic properties of the Zn-free Sm−Fe−N magnets included an HcJ of 0.86 MA·m−1 and a (BH)max of 188 kJ·m−3, while the Zn-bonded (10 wt%) Sm−Fe−N magnets exhibited excellent magnetic properties with a (BH)max of 200 kJ·m−3 and an HcJ of 1.28 MA·m−1. Compared with previous studies, this is the high (BH)max observed for a Sm−Fe−N bulk magnet simultaneously displaying a high HcJ. The (BH)max of the Zn-bonded magnets was greater than that of the Zn-free magnets owing to the higher relative density of the former. Therefore, Zn is an effective binder for increasing not only the coercivity but also the density of Sm−Fe−N magnets. Consequently, the procedure reported herein permits the successful preparation of high-performance Sm−Fe−N bulk magnets.

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Magnetic Phenomena
  • N. Yasuda, S. Kittaka, Y. Kono, T. Sakakibara, K. Kakizaki, K. Kamishi ...
    2020 Volume 44 Issue 3 Pages 70-74
    Published: May 01, 2020
    Released: May 01, 2020
    [Advance publication] Released: April 09, 2020
    JOURNAL OPEN ACCESS

      We investigated the synthesis conditions and magnetic properties of M-Ti substituted Ba12Fe28Ti15O84 with initial compositions of Ba12Fe28-2xTi15+xMxO84 (M = Zn, Mg, Ni, Cu, and Co) sintered at 1100-1300°C. The highest substitution amounts of M-Ti for Fe were consistent with the Ti-ion preference of each transition metal site reported before, suggesting that substituted Ti ions also preferred the sites with high Ti-ion occupancies. The spontaneous magnetizations and Curie temperatures were decreased as the substitution amount x was increased, which means that the substitution weakened the super-exchange interactions between Fe-O-Fe. The highest Zn-Ti substitution rate was lower than the other M-Ti substitution rates, which implies that Zn ions tend to enter specific M(2) and M(14) sites in Ba12Fe28Ti15O84. The sweep of the magnetic field from 0 to 80 kOe changed the relative dielectric constant of Ba12Fe28Ti15O84 by 0.283%. This variation of the dielectric constant caused by the application of magnetic fields is not negligible, showing that this compound should be categorized as a multiferroic material.

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Thin Films, Fine Particles, Multilayers, Superlattices
  • S. Goto, H. Kura, H. Yanagihara
    2020 Volume 44 Issue 3 Pages 75-78
    Published: May 01, 2020
    Released: May 01, 2020
    [Advance publication] Released: April 09, 2020
    JOURNAL OPEN ACCESS

      The nitrogen insertion and topotactic extraction (NITE) method was used to explore an unknown metastable phase of an FeNi alloy with an Fe:Ni ratio of 1:1. We found that partly ordered non-equilibrium L12-FeNi can be obtained through Fe2Ni2N as the intermediate nitride phase. The experimental results of both x-ray diffraction and transmission electron microscopy with energy dispersive x-ray spectrometry are consistent in identifying the denitrided material as L12-FeNi. Ni atoms preferentially occupy the corner sites in an estimated 96% of cases. No significant difference was found in the magnetization curves between the precursor of A1-FeNi and L12-FeNi particles. Our results suggest that the NITE method is not only a useful way for synthesizing fully ordered alloys of equilibrium phases such as L10-FeNi but also for creating metastable phases like L12-FeNi.

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Measurement Technique, High-Frequency Devices
  • D. Oyama, Y. Adachi, M. Miyamoto, N. Ono, A. Imamura, D. Watanabe
    2020 Volume 44 Issue 3 Pages 79-86
    Published: May 01, 2020
    Released: May 01, 2020
    [Advance publication] Released: April 09, 2020
    JOURNAL OPEN ACCESS

      We experimentally revealed that a direct current (DC) biased excitation method can reduce the noise in parallel fluxgate magnetometers composed of a permalloy ring core. The noise suppression was achieved by decreasing the Barkhausen noise and increasing the open-loop sensitivity using the nonlinearity of the B-H curve with the DC-biased excitation. The noise performance depends on the excitation parameters: frequency, amplitude, and DC-bias. We proposed that the parameters should be determined based on the evaluation of the sensitivity and noise level in both open-loop and closed-loop modes. Specifically, a contour map of the closed-loop noise is useful for understanding the noise decrease with different values of the amplitude and DC-bias. We also demonstrated the effectiveness of the DC-biased excitation method using a commercially available fluxgate magnetometer (APS520A, Applied Physics Systems). Using the DC-biased excitation method, the noise level was approximately one-fourth compared to that of the original electronics.

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