Showing papers by "Seong-Cho Yu published in 2010"
TL;DR: In this paper, a tri-critical point with critical exponents (β = 0.26−±-0.01, γ = 1.06−±−0.02) at the tricritical point was demonstrated.
168 citations
TL;DR: In this paper, the room-temperature photoluminescence (PL) properties of many nanostructured ZnO samples grown by chemical vapour deposition (CVD) were studied.
42 citations
TL;DR: In this article, the structural, optical, and magnetic properties of Zn1−xMnxO nanorods were studied based on thermal diffusion and x-ray diffraction.
Abstract: We prepared Zn1−xMnxO nanorods by thermal diffusion. These samples were then studied the structural, optical, and magnetic properties. The structural analyses basing on x-ray diffraction and transmission electron microscope revealed the absence of Mn-related secondary phases. The study of photoluminescence spectra revealed the blueshift in the UV emission when the Mn doping concentration was increased, as a consequence of the extension of the band gap energy. Besides this situation, the increase in emission intensity associated with extrinsic defects at about 680 nm also took place. Concerning the Raman scattering spectra, apart from conventional phonon modes related to the ZnO wurtize-type structure, there were some additional modes introduced by the doping. Their origin was assessed carefully. Particularly, the shift in peak position of E2(high) toward low frequencies due to the increase in the Mn doping concentration could be explained well by means of the spatial correlation model. Magnetic measuremen...
36 citations
TL;DR: In this paper, the magnetic properties of x at.% Co-doped rutile TiO 2 nanoparticles (with x = 1.0, 3.0, 5.0 ) synthesized by the sol-gel technique were studied.
8 citations
7 citations
TL;DR: In this article, a spontaneous domain wall motion in ferromagnetic nanowires at zero external magnetic field was explored by means of micromagnetic simulation, and the spontaneous zero-field wall motion was explained based on the minimization condition of the magnetostatic energy.
Abstract: We have explored a spontaneous domain wall motion in ferromagnetic nanowire at zero external magnetic field by means of micromagnetic simulation. Very interestingly, even with no external magnetic field, a spontaneous domain wall motion is observed with a speed about few tens of m/s, which is significant and not negligible in analysis of the domain wall dynamics on nanowires. The spontaneous zero-field wall motion is explained based on the minimization condition of the magnetostatic energy, preferring to have a wire magnetically saturated. Average speed of the spontaneous wall motion is found to increase as the wire thickness increases.
7 citations
TL;DR: Three-dimensional spin configurations in ferromagnetic nanocubes are investigated using micromagnetic simulation with variation of cube geometry to find the complex spin structure with a spontaneously broken symmetry.
Abstract: We have systematically investigated three-dimensional spin configurations in ferromagnetic nanocubes using micromagnetic simulation with variation of cube geometry. For thin cuboids, a spin configuration exhibits a four-domain Landau state with a magnetic vortex structure at the center as in the case of a thin film square. For a thick cube, a complex spin configuration with an S-type cylindrically asymmetric vortex having two cores on a pair of surfaces while a leaf-like and a C-type states are observed on the other two pairs of cube surfaces. Competition between the geometrical symmetry and magnetic energy minimization condition in ferromagnetic nanocubes leads to the complex spin structure with a spontaneously broken symmetry.
4 citations
4 citations
01 Jan 2010
TL;DR: In this article, the structural, optical, and magnetic properties of ZnO nanorods were studied based on thermal diffusion and x-ray diffraction and transmission electron microscopy.
Abstract: We prepared Zn 1�x Mn x O nanorods by thermal diffusion. These samples were then studied the structural, optical, and magnetic properties. The structural analyses basing on x-ray diffraction and transmission electron microscope revealed the absence of Mn-related secondary phases. The study of photoluminescence spectra revealed the blueshift in the UV emission when the Mn doping concentration was increased, as a consequence of the extension of the band gap energy. Besides this situation, the increase in emission intensity associated with extrinsic defects at about 680 nm also took place. Concerning the Raman scattering spectra, apart from conventional phonon modes related to the ZnO wurtize-type structure, there were some additional modes introduced by the doping. Their origin was assessed carefully. Particularly, the shift in peak position of E2high toward low frequencies due to the increase in the Mn doping concentration could be explained well by means of the spatial correlation model. Magnetic measurements proved the samples with Mn concentrations above 1.15 at. % exhibiting the weak-ferromagnetic order at low temperatures. The nature of the ferromagnetism was discussed by means of the results of the structural and optical investigations. © 2010 American Institute of Physics. doi:10.1063/1.3478709
4 citations
TL;DR: In this article, the authors investigated a damped oscillatory behavior of domain wall propagation in wavy nanowires under an external field higher than the Walker breakdown field using micromagnetic simulation.
Abstract: We have investigated a damped oscillatory behavior of domain wall propagation in wavy nanowires under an external field higher than the Walker breakdown field using micromagnetic simulation. In nanowires having sinusoidal edge distortions with variation of wavelengths, domain wall has been observed to pseudomorphically follow the sinusoidal wires with keeping an intrinsic transformational frequency of inner wall spin structure. Oscillation amplitude of the domain wall position decreases as the wavelength of the wire decreases by an interaction between the periodically distributed spins and the propagating domain wall. Oscillatory behavior of the domain wall position is found to decay in a wire having the wavelength well matching with an intrinsic transformational frequency of the propagating domain wall.
4 citations
TL;DR: In this paper, the structural evolution of Fe50Cr50 metastable alloys was analyzed by the extended x-ray absorption fine structure (EXAFS) with milling periods of 1, 2, 4, 6, 12 and 24 hours.
Abstract: Fe50Cr50 metastable alloys were prepared by the mechanical alloying method with milling periods of 1, 2, 4, 6, 12 and 24 hours, respectively. The structural evolution was analyzed by the extended x-ray absorption fine structure (EXAFS). In this work, the EXAFS analysis provided the local structural information around Fe central atom. The saturation magnetization was also measured by VSM. The magnetization decreased as the process mechanical alloying progressed. The magnetic property was related to the local structural variation as a function of processing time. The analysis showed that the diffusion Cr atoms into Fe clusters caused the reduction of magnetization. EXAFS analysis exhibited that the local ordering of magnetic atoms caused the magnetic ordering. Also, EXAFS analysis showed that the long range order of Fe atoms was destroyed completely in 24 hour milling.
TL;DR: In this article, the influence of the annealing temperature (Tan) on electron spin resonance (ESR) spectra of 2.0 wt.% Mn-doped metal oxides MO (Mn : MO, with M = Mg, Ca, Sr, Ba, Zn and Ni) and TiO2 2 was analyzed.
Abstract: This work presents the influence of the annealing temperature (Tan) on electron spin resonance (ESR) spectra of 2.0 wt.% Mn-doped metal oxides MO (Mn : MO, with M = Mg, Ca, Sr, Ba, Zn and Ni) and TiO2 annealed at temperatures Tan = 400°C - 1150°C. Experimental data obtained reveal that their ESR spectra depend strongly on Tan. There is a temperature value Ttr located in between 600°C and 800°C, where characteristic spectra of samples have a change in shape. For samples MgO:Mn, CaO:Mn and ZnO:Mn, their spectra at temperatures Tan ? Ttr show the Mn2+ hyperfine lines, revealing the substitution of Mn2+ into Mg2+, Ca2+ and Zn2+ sites in the host lattices MgO, CaO and ZnO, respectively. However, such features are absent from samples SrO:Mn, BaO:Mn, NiO:Mn and TiO2 : Mn, where their spectra can be a symmetrical single line (for SrO:Mn, BaO:Mn and TiO2 : Mn) or an asymmetrical line (for NiO:Mn). At temperatures Tan < Ttr, the spectra of the samples usually consist of two lines, one is attributed to MnO2 with the paramagnetic behavior, and the other is assigned to a ferromagnetic (and/or antiferromagnetic) phase probably caused by a magnetic correlation present at the interface between Mn and MnO2 formed by the annealing.
01 Jan 2010
TL;DR: In this paper, the structural evolution of Fe50Cr50 metastable alloys was analyzed by the extended x-ray absorption finest structure (EXAFS) and the saturation magnetization was measured by VSM.
Abstract: (Received 30 April 2010, Received in final form 23 June 2010, Accepted 5 July 2010)Fe50Cr50 metastable alloys were prepared by the mechanical alloying method with milling periods of 1, 2, 4, 6,12 and 24 hours, respectively. The structural evolution was analyzed by the extended x-ray absorption finestructure (EXAFS). In this work, the EXAFS analysis provided the local structural information around Fe cen-tral atom. The saturation magnetization was also measured by VSM. The magnetization decreased as the pro-cess mechanical alloying progressed. The magnetic property was related to the local structural variation as afunction of processing time. The analysis showed that the diffusion Cr atoms into Fe clusters caused the reduc-tion of magnetization. EXAFS analysis exhibited that the local ordering of magnetic atoms caused the mag-netic ordering. Also, EXAFS analysis showed that the long range order of Fe atoms was destroyed completelyin 24 hour milling.Keywords : Fe50Cr50, mechanical alloy, magnetization, local structure
TL;DR: In this article, the magnetic properties and structure of Ni45Al45C10 nanocrystalline alloys prepared by the mechanical alloying process are studied as a function of milling time.
Abstract: The magnetic properties and structure of Ni45Al45C10 nanocrystalline alloys prepared by the mechanical alloying process are studied as a function of milling time. The milling times are 1, 2, 4, 6, and 12 h. The effect of milling time on structural characterization was investigated by an X-ray diffractometer (XRD) and extended X-ray absorption fine structure spectroscopy (EXAFS). Both XRD and EXAFS studies showed that the alloying process occurred after 4-h milling. The nano particle size and shape are examined by scanning electron microscopy. Magnetic properties are examined by vibrating sample magnetometer. Magnetic saturation is decreased with milling time, which seemed be due to substitution of Ni atoms by Al or C atoms resulting in magnetic dilution and/or decreasing of particle size. The coercivity (Hc) is decreased with milling time indicating the increase in single-domain size owing to the crystallite size reduction.