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Suhk Kun Oh 한국물리학회 2016 New Physics: Sae Mulli Vol.66 No.5
The time evolution of classical van der Waals spins in the presence of a heat bath consisting of a chain of one-dimensional classical harmonic oscillators, with the coupling term $ - S_z^2 \sum c_k x_k$, was studied. The exact harmonic oscillator bath variables, the averages of the total spin components, were obtained, and the relaxation behaviors of the total spin components in the system were examined. The bath variables averages of the x- and the y-components of the total spin showed no amplitude relaxation, but an interesting phase-angle relaxation was observed. The phase angles of the x- and the y-components of the total spin showed a transient, damped, oscillating behavior before settling to a steady increase with time; however, the z-component of the total spin remained constant.
Suhk Kun Oh 한국물리학회 2016 새물리 Vol.66 No.5
The nonequilibrium relaxation behaviors of noninteracting classical spins in a longitudinal magnetic field coupled to D(=1,2,3)-dimensional Debye heat baths were studied to see whether the dimensionality of the Debye heat baths significantly affected their behaviors. For the case of a one-dimensional Debye heat bath, the relaxation of the classical spins was manifested as a phase-angle relaxation in a manner almost identical to that of the heat bath consisting of a one-dimensional chain of classical harmonic oscillators. Nevertheless, for the cases of two- and three-dimensional Debye heat baths coupled to the classical spins, discontinuities in the phase-angle relaxation of the total spin components suddenly occured at time $t=0$.
Park, Chanae,Kim, Juhwan,Lee, Kangil,Oh, Suhk Kun,Kang, Hee Jae,Park, Nam Seok The Korean Vacuum Society 2015 Applied Science and Convergence Technology Vol.24 No.3
Nickel oxide (NiO) thin films were grown on soda-lime glass substrates by RF magnetron sputtering method at room temperature (RT), and they were post-annealed at the temperatures of $100^{\circ}C$, $200^{\circ}C$, $300^{\circ}C$ and $400^{\circ}C$ for 30 minutes in vacuum. The electronic structure, optical and electrical properties of NiO thin films were investigated using X-ray photoelectron spectroscopy (XPS), reflection electron energy spectroscopy (REELS), UV-spectrometer and Hall Effect measurements, respectively. XPS results showed that the NiO thin films grown at RT and post annealed at temperatures below $300^{\circ}C$ had the NiO phase, but, at $400^{\circ}C$, the nickel metal phase became dominant. The band gaps of NiO thin films post annealed at temperatures below $300^{\circ}C$ were about 3.7 eV, but that at $400^{\circ}C$ should not be measured clearly because of the dominance of Ni metal phase. The NiO thin films post-annealed at temperatures below $300^{\circ}C$ showed p-type conductivity with low electrical resistivity and high optical transmittance of 80% in the visible light region, but that post-annealed at $400^{\circ}C$ showed n-type semiconductor properties, and the average transmittance in the visible light region was less than 42%. Our results demonstrate that the post-annealing plays a crucial role in enhancing the electrical and optical properties of NiO thin films.
Dede Djuhana,Bambang Soegijono,Hong-Guang Piao,Suhk Kun Oh,Seong Cho Yu,김동현 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.63 No.3
We have investigated the domain wall (DW) depinning behavior around the symmetric notches inferromagnetic nanowires by means of a micromagnetic simulation. We observed that the depinningfield decreases as the size of the notch increases. The change in the ratio of the height to the lengthof the bottom of the triangular notch is also considered, and a relatively insensitive variation of thedepinning field is observed with for ratios greater than 2. When the depinning field strength is varied,the DW internal structure is found to change during the depinning process. At a lower depinningfield (< 4 mT), the DW keeps its initial transverse wall structure whereas at a higher depinningfield (> 4 mT), the DW is depinned with a transformation of the inner structure with an antivortexsoon after the DW has escaped from the notch due to the Walker breakdown phenomenon. Veryinterestingly, with any external field, the depinned DW with antivortex inner structure is observedto move back to the original notch position. This is explainable because the notch acts as anattractive pinning potential for the DW.