• Journal of Magnetics
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• 제9권2호
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• pp.60-64
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• 2004

In this paper calculations of magnetisation and magnetoresistance characteristics of the Spin Valve (SV) and Pseudo Spin Valve (PSV) spintronics structures are reported and compared with the experimental data. The magnetisation reversal process was analysed with respect to the Stoner- Wohlfahrt model of total surface energy in terms of uniaxial anisotropy, exchange coupling between ferromagnetic layers, unidirectional exchange anisotropy of pinned layer (modelled by exchange coupling between magnetisation of pinned layer and net magnetisation of antiferromagnetic layer with high anisotropy). The numerical simulation of the model to the experimental magnetisation data yielded the above parameters for SV and PSV structures. These parameters were used to more sophistically micromagnetic modelling tool originating from the project called Object Oriented Micromagnetic Framework. Influence of the shape anisotropy of the Magnetic Tunnelling Junction cell used in MRAM was simulated by means of micromagnetic simulations. Results were compared to those obtained from the spot Kerr measurements.

• 한국자기학회:학술대회 개요집
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• 한국자기학회 2003년도 하계학술연구발표회 및 한.일 공동심포지엄
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• pp.150-151
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• 2003

In the past years, a giant magnetoresistance (GMR) effect found in perovskite-like structured materials has attracted considerable attention among scientists and manufacturers, since, a practical point of view, the capacity of producing magnetic and sensing sensors. In a stream of this interest, further efforts to understand the underlying mechanism that leads to the GMR effect relative to the correlation between transport and magnetic properties, have been extensively devoted. In these cases, spin-glass-like behaviors are ascribed to the frustration of random competing exchange interactions, namely the ferromagnetic double-exchange interaction between Co$\^$3+/ (or Mn$\^$3+/) and Co$\^$4+/(or Mn$\^$4+/) and the antiferromagnetic one like spins. Noticeably, the distinction of spin-glass region from cluster-glass one, involved in the remarkable changes in transport and magnetic properties at a critical value of doping concentration, was observed. Magnetic anomalies in zero-field-cooled (ZFC) magnetization as well as ac magnetic susceptibility below Curie temperature T$\sub$c/ and the charge/orbital fluctuation were also realized. In this work, we present a study of magnetic properties of a deficient manganese perovskites system of La$\sub$0.6/Sr$\sub$x/MnTi$\sub$y/O$_3$, and particularly provide its new magnetic phase diagram.

• Progress in Superconductivity
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• 제7권1호
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• pp.1-5
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• 2005

A pseudogap in the normal-state quasiparticle density of states of $high-T_c$ superconductors has been revealed in many different kinds of experiments. The existence of the pseudogap and the superconducting gap, and the correlation between them has attracted considerable attention because they are believed to be a key to understanding the mechanism of the $high-T_c$ superconductivity. The interlayer tunneling spectroscopy, excluding the surface-dependent effect, is one of the most accurate means to examine the electron spectral characteristics both in the superconducting and the normal states. In this study, a new constant-temperature intrinsic tunneling spectroscopic technique, excluding the overheating effect using the in-situ temperature monitoring combined with the digital proportional-integral-derivative control, is introduced. The implication on the $high-T_c$ superconductivity of the detailed temperature dependencies of the observed spectral weight in $Bi_{2}Sr_{2}CaCu_{2}O_{8+x}\;high-T_c$ material for overdoped and underdoped levels is discussed.

• 한국세라믹학회지
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• 제45권3호
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• pp.179-184
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• 2008

(40-x)BaO${\cdot}xFe_2O_3{\cdot}60P_2O_5$ glasses with $5{\leq}x{\leq}35mol%$ were investigated by ESR spectroscopy. Two resonances observed near g=2.0 and g=4.3. The line at g=4.3 disappeared with the increase of the $Fe_2O_3$ content. The resonance at $g{\approx}2.0$ displayed characteristic signal consisting of superposed extremely broad and narrow components. The broader one indicates the presence of the association of two or more $Fe^{3+}$ ions, antiferromagnetically and the narrow one is related to the microclusters involving iron ions. Temperature dependence of the ESR integrated intensity revealed short-range antiferromagnetic character for $x{\geq}15mol%$.

• Rapid Communication in Photoscience
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• 제4권1호
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• pp.25-28
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• 2015

The time-resolved photoexcitation dynamics of electrical conductivity of the magnetic organic superconductor ${\lambda}-(BETS)_2Fe_{0.45}Ga_{0.55}Cl_4$ has been studied with a nanosecond visible laser pulse at its three different phases, i. e., metallic phase, superconducting phase and insulating phase. A transient increase of the resistance is induced by photoirradiation at all the temperatures measured for all three phases, but the decay profile shows a significant temperature dependence. The relaxation rate in the metallic and insulating phase are different from each other, and the decay time is relatively faster and almost constant in the metallic phase. However, a prolongation of the relaxation time is observed at temperature just around the narrow superconducting phase. Nonbolometric (nonthermal) origin of the observed photoresponse of the electrical conductivity is confirmed in the superconducting phase.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2012년도 제42회 동계 정기 학술대회 초록집
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• pp.204-204
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• 2012

Peierls instability and spin ordering of zigzag graphene nanoribbons (GNR) created on a fully hydrogenated graphene (graphane) are investigated as a function of their width using first-principles density-functional calculations within the generalized-gradient approximation. For the width containing a single zigzag C chain (N=1), we find the presence of a Peierls instability with a bond alternated structure. However, for width greater than N=1, the Peierls distortion is weakened or disappears because of the incommensurate feature of Fermi surface nesting due to the interaction of C chains. Instead, there exists the antiferromagnetic (AFM) spin ordering in which the edge states are ferromagnetically ordered but the two ferromagnetic (FM) edges are antiferromagnetically coupled with each other, showing that electron-lattice coupling and spin ordering in GNR are delicately competing at an extremely thin width of N=2. It is found that, as the width of GNR increases, the energy gain arising from spin ordering is enhanced, but the energy difference between the AFM and FM (where two edge states are ferromagnetically coupled with each other) orderings decreases.

• Journal of Electrochemical Science and Technology
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• 제6권1호
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• pp.16-25
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• 2015

Transition metal oxide nanocrystalline materials are playing major role in energy storage application in this scenario. Nickel oxide is one of the best antiferromagnetic materials which is used as electrodes in energy storage devices such as, fuel cells, batteries, electrochemical capacitors, etc. In this research work, nickel oxide nanoparticles were synthesized by combustion route in presence of organic fuels such as, glycine, glucose and and urea. The prepared nickel oxide nanoparticles were calcined at 600℃ for 3 h to get phase pure materials. The calcined nanoparticles were preliminarily characterized by XRD, particle size analysis, SEM and EDAX. To prepare nickel oxide electrode materials for application in supercapacitors, the calcined NiO nanoparticles were mixed with di-methyl-acetamide and few drops of nafion solution for 12 to 16 h. The above slurry was coated in the graphite sheet and dried at 50℃ for 2 to 4 h in a hot air oven to remove organic solvent. The dried sample was subjected to electrochemical studies, such as cyclic voltammetry, AC impedance analysis and chrono-coulometry studies in KOH electrolyte medium. From the above studies, it was found that nickel oxide nanoparticles prepared by combustion synthesis using glucose as a fuel exhibited resulted in low particle diameter (42.23 nm). All the nickel oxide electrodes have shown better good capacitance values suitable for electrochemical capacitor applications.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2002년도 추계학술대회 논문집 Vol.15
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• pp.260-263
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• 2002

There is great interest in developing magnetoresistance(MR) sensor, using ferromagnetic, electrically non-magnetic conducting and antiferromagnetic films, especially for the use in weak magnetic fields. Here, we report single and Wheatstone-bridge type of MR sensors made in Si(001)/NiO($300{\AA}$)/NiFe bilayers. Angular dependence of MR profiles was measured in Si(001)/NiO($300{\AA}$)/NiFe($450{\AA})$ films as a function of an angle between current and applied field direction, also, linearity was determined. AMR characteristics of single MR sensors was well explained with single domain model. Good linearity in $45^{\circ}$ Wheatstone-bridge type of MR sensors consisting of 4 single MR sensors made in Si(001)/NiO($300{\AA}$)/NiFe($450{\AA})$ was shown in the range of about ${\leq}{\pm}5$ Oe.

• Journal of Magnetics
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• 제10권2호
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• pp.52-57
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• 2005

In this research, magnetoresistance (MR) ratio (MR), resistivity, and exchange coupling field $(H_{ex})$ behaviors for sputter deposited spin valves with FeMn antiferromagnetic layer have been extensively investigated by rapid thermal annealing (RTA) as well as conventional annealing (CA) method. 10 s of RTA revealed that interdiffusion was not significant up to $325^{\circ}C$ at the interfaces between the layers when the RTA time was short. The MR of FeMn spin valves were reduced when the spin valves were exposed to temperature of $250^{\circ}C$, even for a short time period of 10 s prior to CA. $H_{ex}$ was maintained up to $325^{\circ}C$ of CA when the specimen was subjected to 10 s of RTA at $200^{\circ}C$ prior to CA, which is $25^{\circ}C$ higher than the result obtained from the CA without prior RTA. Therefore, the stability of $H_{ex}$ could be enhanced by a prior RTA before performing CA up to annealing temperature of $325^{\circ}C$. MR and sensitivity of the specimens annealed without magnetic field up to $275^{\circ}C$ were recovered to the values prior to CA, but $H_{ex}$ was not recovered. This means that reduced MR sensitivity and MR during the device fabrication can be recovered by a field RTA.

• 한국자기학회지
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• 제24권4호
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• pp.97-100
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• 2014

분자자성체 Mn-dimer의 전기구조 및 자기적 성질을 제1원리의 범밀도함수법을 이용하여 계산하였다. 계산 된 결과, 전자구조는 벌크 MnO와 비슷한 Mn 주위의 4개의 산소 원자에 의해 $t_{2g}$, $e_g$ 에너지 준위로 분리되어 있었다. 적은 수의 배위원자로 이 결정장 분리는 작았디. 총에너지 계산에서는 반강자성적 상호작용이 낮은 에너지를 가지고 있었다. 계산 된 $Mn^{+2}$ 원자 사이의 교환상호작용 크기는 다른 Mn-O 분자자성체보다 한 단위 큰 값을 얻었다. 이 원인은 Mn 3d 사이의 직접 상호작용과 Mn-O의 강한 결합으로 인한 초교환상호작용의 결과이다.