• Title/Summary/Keyword: magnetization dynamics

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Effect of Nucleation and Growth Dynamics on Saturation Magnetization of Chemically Synthesized Fe Nanoparticles

  • Ogawa, T.;Seto, K.;Hasegawa, D.;Yang, H.T.;Kura, H.;Doi, M.;Takahashi, M.
    • Journal of Magnetics
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    • v.16 no.3
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    • pp.308-311
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    • 2011

  • In order to obtain mono-dispersed Fe NPs with high saturation magnetization, quantitative analysis method to investigate the growth dynamics of the Fe NPs synthesized by a conventional thermal decomposition method has been developed. As a result, fast nucleation process promotes formation of ~4 nm of initial nucleus with a non-equilibrium phase, resulting in low saturation magnetization. And slow particle growth with atomic-scaled surface precipitation mode (< 100 atoms/($min{\cdot}nm^2$)) can form the growth layer on the surface of initial nucleus with high saturation magnetization (~190 emu/$g_{Fe}$) as an equilibrium a phase of Fe. Therefore, higher stabilization of small initial nucleus generated just after the injection of $Fe(CO)_5$ should be one of the key issues to achieve much higher $M_s$ of Fe NPs.

  • https://doi.org/10.4283/JMAG.2011.16.3.308 인용 PDF KSCI

The vortex dynamics in $Bi_2$$Sr_2$Ca$Cu_2$$O_8$single crystals unirradiated and with low-density columnar defect (저밀도 원통형 결함이 $Bi_2Sr_2CaCu_2O_8$ 단결정의 볼텍스 동역학에 미치는 영향)

  • Lee, T.W.;Lee, C.W.;Shim, S.Y.;Ha, D.H.;Kim, D.H.
    • Progress in Superconductivity
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    • v.3 no.1
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    • pp.36-40
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    • 2001

  • We have studied vortex dynamics in$ Bi_2$$Sr_2$$CaCu_2$O$_{8}$single crystals of unirradiated and irradiated samples by using 100 $\times$ $100\mu\textrm{m}^2$Hall sensor. Doses equivalent magnetic fields are 20 G, 100 G and 1 kG. In the magnetization measurement, a second magnetization peak (SMP) was observed in unirradiated, 20 G dose and 100 G dose samples in contrast to 1 kG dose sample. In the unirradiated sample, the SMP was observed in the range of 18 K ~ 35 K and the amplitude of the SMP decreased with increasing temperature. With increase of the irradiation dose, temperature region and sharpness of the SMP were reduced. In the magnetic relaxation measurement, we observed that the normalized relaxation rate S decreased with increasing the irradiation dose. Our results suggest that the vortex dynamics is not greatly affected by low-density columnar defects.s.

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Negative Dynamic Resistance and RF Amplification in Magnetic Tunnel Junctions

  • Tomita, Hiroyuki;Maehara, Hiroki;Nozaki, Takayuki;Suzuki, Yoshishige
    • Journal of Magnetics
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    • v.16 no.2
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    • pp.140-144
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    • 2011

  • We report on a numerical calculation study of two new functional properties in magnetic tunnel junctions (MTJs), negative dynamic resistance and RF amplification. The magnetic dynamics in a conventional CoFeB/MgO/CoFeB MTJ with in-plane magnetization was investigated using a macro-spin model simulation. To examine the influence of thermal fluctuations, random external magnetic fields were also included. Using a voltage controlled bias circuit, the negative dynamic resistance was obtained from time averaged I-V characteristics at both 0 K and 300 K under appropriate external magnetic fields and bias voltages. Using this negative dynamic resistance property, we demonstrated RF amplification with a 100 MHz high frequency signal. Sizable RF amplification gain was observed without thermal fluctuation. However, at 300 K, the RF signal was not amplified because low frequency magnetization dynamics were dominant.

  • https://doi.org/10.4283/JMAG.2011.16.2.140 인용 PDF KSCI