• Proceedings of the Korean Magnestics Society Conference
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• 2011.12a
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• pp.14-14
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• 2011

Limited understanding of the surface properties of $Pt_3Ni$ for the oxygen reduction reaction (ORR) in polymer electrolyte membrane fuel cell (PEMFC) has motivated the study of magnetic properties and electronic structures of Pt segregated $Pt_3Ni$ (111) surface during adsorption of oxygen molecule on it. The first principle method based on density functional theory (DFT) is carried out. Nonmagnetic Pt has induced magnetic moment due to strong hybridization between Ni 3d and Pt 5d. It is found that an oxygen molecule prefers bridge site with Pt rich subsurface environment for adsorption on the surface of Pt segregated $Pt_3Ni$ (111). It is seen that there is very small charge transfer from $O_2$ to Pt. The curve of energy versus magnetic moment of the oxygen explains the magnetic moments in transition states. We found the dissociation barrier of 1.07eV significantly higher than dissociation barrier 0.77eV on Pt (111) suggesting that the dissociation is more difficult on Pt segregated $Pt_3Ni$ (111) surface. The spin polarized densities of states are presented in order to understand electronic structures of Pt and $O_2$ during the adsorption in detail.

• Journal of the Korean Magnetics Society
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• v.22 no.4
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• pp.117-120
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• 2012

Compounds such as NaN belong to an interesting class of materials in which a magnetic order may appear despite the lack of d electrons. The magnetic properties of these materials are ascribed to the partially filled p shells. Recently, on the basis of electronic structure calculations from first principles, it has been found that NaN is a ferromagnetic half-metal in rocksalt (RS) and zinc-blende (ZB) structures with half-metallic band gaps in majority electron channels. The former structure has appeared to be more stable. From the first-principles calculation, we found that the half-metallic properties of the bulk RS and ZB NaN are conserved at the RS(001) and ZB(110) surfaces. Due to the interactions between Na s and N p electrons, N atoms become positively polarized. In the RS NaN (001) the calculated values of the magnetic moments of the N atoms is about $0.73{\mu}_B$. The magnetic moment on the N atom in the top most layer of ZB(110) is slightly larger than that of the RS(001) surface, i.e., $0.75{\mu}_B$. The Na atoms in the both structure are hardly polarized.

• Korean Journal of Materials Research
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• v.13 no.1
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• pp.48-52
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• 2003

The substituted yttrium iron garnet systems $Y_{ 3-x}$/Gd$_{x}$X$0.2_{0.2}$ $Fe_{4.8}$ $O _{12}$ (x = 0.2, 0.4, 0.6) have been investigated by means of X-ray diffraction, Mossbauer spectroscopy and SQUID. The X-ray diffraction patterns at room temperature confirm the samples to have a single phase of the garnet structure over the whole composition range. The lattice constants of all the samples linearly change with increasing x due to the size of substituted ions in the dodecahedral sites. $Y_{3-x}$ $Gd_{x}$ X$Fe_{4.8}$ $In_{0.2}$ $O_{12}$ system which $Y_{3-x}$ ions are substituted with Gd$^{ 3＋}$ ions, the Mossbauer spectrum consists of three Zeeman sextets at room temperature, one due to the $Fe^{3＋}$ ions on the octahedral(a-) sites and the others due to the $Fe^{3＋}$ ions on the tetrahedral(d-, d'-) sites, respectively. From the hysteresis loop measured by means of SQUID over the whole composition range, the saturation magnetization $M_{s}$ and magnetic moments $\mu_{ B}$ per unit cell have been obtained. The increment of Gd-ion content causes $M_{s}$ and $\mu_{B}$ decrease while the increment of In-ion content does not.

• Current Applied Physics
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• v.18 no.11
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• pp.1190-1195
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• 2018

By employing soft X-ray magnetic circular dichroism (XMCD), soft X-ray absorption spectroscopy (XAS), and photoemission spectroscopy (PES), we have investigated the electronic structure of the candidate zero-moment half-metallic $Mn_3Ga$. We have studied the ball-milled and annealed $Mn_3Ga$ powder samples that exhibit nearly zero magnetization. Mn 2p XAS revealed that Mn ions in $Mn_3Ga$ are nearly divalent for both of the Mn ions having the locally octahedral symmetry and those having the locally tetrahedral symmetry. The measured Mn 2p XMCD spectrum of $Mn_3Ga$ is very similar to that of ferrimagnetic $MnFe_2O_4$ having divalent Mn ions. The sum-rule analysis of the Mn 2p XMCD spectrum shows that both the spin and orbital magnetic moments of Mn ions in $Mn_3Ga$ are negligibly small, in agreement with the nearly compensated-ferrimagnetic ground state of $Mn_3Ga$. The valence-band PES spectrum of $Mn_3Ga$ agrees well with the calculated density of states, supporting the half-metallic electronic structure of $Mn_3Ga$.

• Proceedings of the IEEK Conference
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• 1998.06a
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• pp.106-109
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• 1998

Wireless communication systems, in particular, must operate in a crowded electro-magnetic environmnet where in-band undesired signals are treated as noise by the receiver. These interfering signals are often random but not Gaussian Due to nongaussian noise, the distribution of the observables cannot be specified by a finite set of parameters; instead r-dimensioal sample space (pure noise samples) is equiprobably partitioned into a finite number of disjointed regions using quantiles and a vector quantizer based on training samples. If we assume that the detected symbols are correct, then we can observe the pure noise samples during the training and transmitting mode. The algorithm proposed is based on a piecewise approximation to a regression function based on quantities and conditional partition moments which are estimated by a RMSA (Robbins-Monro Stochastic Approximation) algorithm. In this paper, we develop a diversity combiner with modified detector, called Non-Linear Detector, and the receiver has a differential phase detector in each diversity branch and at the combiner each detector output is proportional to the second power of the envelope of branches. Monte-Carlo simulations were used as means of generating the system performance.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.33A no.5
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• pp.85-93
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• 1996

The far-zone scattered field patterns of a hyperbolic reflector antenna are analyzed by using uniform geometrical theory of diffraction(UTD). The main objective of this paper is to obtain the higher order diffraction contributions which provide the continuity over the shadow boundaries of the first order solution. to obtain the scattered magnetic field characteristics, the scattered field components of the secodn-order diffraction, diffraction-reflection, diffraction-reflection-diffraction terms are added to the result of the previous research. The results of the present research are compared to those of the first order solution and the method of moments. One can observe the improvemtn of the current approach over the first order solution. also, the results of the present method agree very well with those of the moment methods especially in the transition regions near the first order diffraction shadow boundaries.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.34D no.9
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• pp.28-35
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• 1997

A novel high-Q vertical jinductor for MMICs is proposed and characterized in a wide range of frequencies (DC~10 GHz) using the numerical methods such as the PeEC(partial equivalent element circuit), the FDM (finite difference method) and the MoM (method of moments). Electrical superiority of the vertical inductor to the horizontal is observed in terms of the magnetic flux linkage and the ground screening effect. The veritcal bondwire inductor is designed in consideration of the wire bonding feasibility and the optimum electrical peformance. This structure is also analyzed using the equivalent circuit and compared with the conventional spiral inductors From the calculated results, high Q-factor, inductance, and cut-off frequency are observed to be inherent characteristics of the veritcal bondwire inductor.

• Journal of the Korean Ceramic Society
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• v.48 no.6
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• pp.577-583
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• 2011

Stabilized biocompatible superparamagnetic iron oxide nanoparticles (SPIONs) were prepared by controlled coprecipitation method for hyperthermia application. ESR measurements determined that all of the interactions in the individual SPIONs (1 nm and 11 nm) were antiferromagnetic in nature because the ions contributed to the magnetization with a range of magnetic moments. In-situ monitoring of the temperature increment was performed, showing that the microwave absorption rate of the SPIONs was dispersed in an appropriate host media (polar or non-polar solvents) during microwave irradiation. Microwave absorption energy rates and heat loss of SPIONs in solvent were calculated by non-linear data fitting with an energy balance equation. The microwave absorption rates of SPIONs dispersed in solvent linearly increases when the concentration of SPIONs increases, implying that the microwave absorption rate can be tunable by changing the concentration of SPIONs.

• Progress in Superconductivity and Cryogenics
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• v.16 no.4
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• pp.17-20
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• 2014

We have investigated the effect of temperature and bias current on the stability of the inverse spin-switch effect in Permalloy(Py)/Nb/Permalloy pseudo spin-valves. The inverse spin-switch operates between two orientations of the ferromagnetic moments of Py layers; parallel (ON) and antiparallel-domain (OFF) state. Measuring time scans of the resistance changes between the ON and OFF state, ${\Delta}R_{ON-OFF}$, while alternating magnetic fields between the two states at various temperatures and bias currents, revealed that enhancement of ${\Delta}R_{ON-OFF}$ is a key factor to achieve successful operation of superconducting spin switch.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.28A no.9
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• pp.680-684
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• 1991

The scattering problem of a transverse electric (TE) plane wave by strip grating with a dielectric slab over a ground plane is analyzed by the method of moments. By use of equivalence principle, surface magnetic current density on the shorted slot is expanded in a series of Chebyshev polynomial a satisfying the appropriate edge condition. Numerical results for reflection coefficient are obtained and compared with other available results. Our numerical results obtained from the present method are in good agreement with other result available in the literature.