• Journal of the Korean Magnetic Resonance Society
• /
• v.10 no.1
• /
• pp.59-73
• /
• 2006

Spin-lattice relaxation pathway of $CH_2$ spin system by two dimensional NOESY sequence has been discussed. Two-dimensional spectra governed by dipolar relaxation mechanism were simulated in term of transfer mode, the generalization of conventionally used magnetization mode in one dimension. The transfer matrix directly related to the Redfield relaxation matrix can be constructed by the multiplet of transfer mode. The observable relaxation transfer modes causes to variation of the off-diagonal signal intensity of phase sensitive NOESY spectra from which variable spectral density can be extracted with simple group theoretical calculation. The variation of the J-coupling peak intensity as a function of the mixing time in 2-D spectra for $n-Undecane-5-^{13}C$ and Bromoacetic $2-^{13}C$ acid has been theoretically traced.

• Journal of the Korean Magnetics Society
• /
• v.5 no.5
• /
• pp.655-658
• /
• 1995

Magnetization behavior of sputter-deposited Co/Pd multilayers were characterized, and it has been found that even when the multilayers are sputtered at low pressure (10 mTorr), the coercivity of the multilayers can be increased to large extent without noticeable change of saturation magnetization by increasing the deposition pressure of Pd underlayer. It turned out that the surface topology of Pd underlayer gets rough as deposition pressure increases, which consequently affects the magnetization reversal mode of Co/Pd multilayers from domain wall motion to magnetic spin rotation. The enhancement of coercivity is attributed to the domain wall pinning effect which is comected with the surface roughness of Pd underlayer on which Co/Pd multilayers grow.

• Proceedings of the Korean Magnestics Society Conference
• /
• 2001.10a
• /
• pp.18-19
• /
• 2001

• Journal of Magnetics
• /
• v.16 no.3
• /
• pp.308-311
• /
• 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.

• Journal of the Korean Magnetics Society
• /
• v.4 no.1
• /
• pp.1-6
• /
• 1994

The magnetization dynamics was investigated by solving possible origins of overdamped susceptibility observed in ultra-soft magnetic amorphous thin films. The experimental high frequency spectrum and computational spectrum calculated from Gilbert's equation of motion were compared in order to find proper damping factor $\alpha{\approx}20$ and demagnetizing coefficients $D_{x}{\approx}D_{y}{\approx}D_{z}{\approx}0$ for ultra-soft magnetic films. A magnetization vortex mode was, then, proposed to explain the origin of the reversible susceptibility and other anomalies of the ultra-soft magnetic heterogeneous thin films. In this mode it is suggested that there occur, within the nanoscale structural features of the ultra-soft films, incoherent rotational spin motions that are highly damped by the energy transfer from short wavelength spin wave modes and local defect structure mode interactions.

• Journal of the Korean Magnetics Society
• /
• v.5 no.5
• /
• pp.524-527
• /
• 1995

The temperature dependence of spin wave mode separation in amorphous $Co_{89.5}Zr_{10.5}$ thin film has been investigated at temperatures between 100 K and 300 K. The magnetization and the spectroscopic splitting factor were obtained for the main resonance mode in parallel and perpendicular magnetic field. ${\Delta}H_{2-3}$, the difference between resonance field of mode 2 and the resonance field of mode 3, increases with decreasing temperature. The linewidth increases for all the modes with decreasing temperature. Especially in mode 3 it increases rapidly below 200 K. This phenomenon could be caused by the increase of exchange stiffness constant or the decrease of surface magnetic anisotropy constant with decreasing temperature.

• Proceedings of the Korean Magnestics Society Conference
• /
• 2011.06a
• /
• pp.23-23
• /
• 2011

• Journal of the Korean Magnetics Society
• /
• v.4 no.3
• /
• pp.256-262
• /
• 1994

$200{\AA}$ thick Co/Pd multilayered thin films were fabricated by sputtering. Two thicknesses of cobalt sublayer, $2{\AA}$ and $4{\AA}$ were chosen and the effects of sputtering pressure on the perpendicular magnetic anisotropy were investigated. It has been found that the optimum pressure for maximum perpendicular magnetic anisotropy(PMA) existed and the pressure for maximum PMA was lower for the multilayer with $2{\AA}$ cobalt layer than that with $4{\AA}$ cobalt thickness. As the sputtering gas presssure increased, domain wall motion with magnetization became difficult and the predominant mode of magnetization reversal changed from domain wall motion to magnetic moment rotation. It turned out that the perpendicular magnetic anisotropy was higher in case of $2{\AA}$ cobalt thickness than $4{\AA}$ cobait thickness.

• Proceedings of the KIEE Conference
• /
• 1999.07a
• /
• pp.259-261
• /
• 1999

In this paper, we investigated the frequency dependences of AC loss and the magnetic properties of a superconductor using magnetization method. We used the YBCO bulk superconductor sample which has a square-shaped cross sectional area of $6mm{\times}6mm$. and 43mm-long in axial direction. The applied AC magnetic field was parallel to the direction of sample axis. It is observed that YBCO bulk has the diamagnetic properties. AC loss calculation of YBCO bulk superconductor was performed by evaluating the total area of magnetization traces. We performed two cases of experiments, one for $B_m<B_p$ and the other for $B_m<B_p$. The experiments showed that the AC loss dependences on frequency were different in each mode, as was indicated in other publications.

• Journal of Electrical Engineering and Technology
• /
• v.9 no.5
• /
• pp.1527-1536
• /
• 2014

This paper investigates the optimal values of turn-on and turn-off angles, and ratio of flux linkage at turn-off angle and peak phase current positions of optimal control for accomplishing maximum output power in an 8/6 Switched Reluctance Generator (8/6 SRG). Phase current waveform is analyzed to determine optimal excitation angles (optimal turn-on and turn-off angles) of the SRG for maximum output power which is applied from a nonlinear magnetization curve in terms of control variables (dc bus voltage, shaft speed, and excitation angles). The optimal excitation angles in single pulse mode of operation are proposed via the analytical model. Simulated and experimental results have verified the accuracy of the analytical model.