G. W. Kim

Changwon National University, Changnyeong, South Gyeongsang, South Korea

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Publications (7)8.37 Total impact

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    ABSTRACT: A detailed investigation of the magnetic and the magnetocaloric properties of La0.7Sr0.3MnO3, La0.7Ca0.3MnO3 and La0.7Ca0.1Sr0.2MnO3 for possible application in magnetic refrigeration is presented. The adiabatic magnetic entropy change was determined for a magnetic field change from 0 to 2.5 T by using magnetization data. A broad table-like entropy change with a relative cooling power of 111 J/kg in an applied magnetic field of 2.5 T with an operating temperature range of 54 K was observed in the La0.7Ca0.1Sr0.2MnO3 sample. The broadening in the magnetic entropy change in La0.7Ca0.1Sr0.2MnO3 is discussed in light of the tricritical mean-field theory. The tricritical exponent (δ) was calculated for the La0.7Ca0.1Sr0.2MnO3 sample and found to be ∼ 4.76 ± 0.03, which is very close to the proposed value δ = 5 for the tricitical exponent. The studied samples can be considered as giant magnetocaloric materials for room-temperature refrigeration.
    Journal- Korean Physical Society 06/2013; 62(12). · 0.51 Impact Factor
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    ABSTRACT: We report microwave assisted hydrothermal synthesis and magnetocaloric properties of La0.67Sr0.33MnO3 manganite. The synthesized La0.67Sr0.33MnO3 nanoparticles was characterized using X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDS) and magnetization measurements. The XRD results indicated that La0.67Sr0.33MnO3 nanoparticles have polycrystalline nature with monoclinic structure. FE-SEM results suggested that La0.67Sr0.33MnO3 nanoparticles are assembled into rod like morphology. Magnetization measurements show that La0.67Sr0.33MnO3 nanoparticles exhibit transition temperature (Tc) above room temperature. The maximum magnetic entropy change (deltaS(M))max was found to be 0.52 J/kg K near Tc approximately 325 K at applied magnetc field of 20 kOe. This compound may considered as potential material for magnetic refrigeration near room temperature.
    Journal of Nanoscience and Nanotechnology 07/2012; 12(7):5523-6. · 1.15 Impact Factor
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    ABSTRACT: The magnetic and electrical properties of (La0.7Sr0.3MnO3)1−x/(CuFe2O4)x have been investigated. The (La0.7Sr0.3MnO3)1-x/(CuFe2O4)x composites with x = 0, 0.01, 0.03, 0.06 and 0.09 wt.% were prepared by conventional solid state reaction method, respectively. The structures, morphology, magnetic and electrical properties of the samples have been studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and physical property measurement system (PPMS). The resistance measured as a function of temperature demonstrates that the pure LSMO samples display metal to semiconductor transition. On the other hand, the others indicated semiconductor/insulator behaviors. The MR was measured in an applied magnetic field of 0.5T. The results clearly show that the magnetoresistance (MR) effect is enhanced at a wide temperature range with CuFe2O4 composition. It may be helpful to improve the low-field magnetoresistance (LFMR) under the influence of the spin-polarized tunneling and the spin-dependent scattering.
    Journal of Physics Conference Series 01/2011; 266(1):012106.
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    ABSTRACT: We report structural, magnetic and electronic structure study of Mn doped TiO2 thin films grown using pulsed laser deposition method. The films were characterized using X-ray diffraction (XRD), dc magnetization, X-ray magnetic circular dichroism (XMCD) and near edge X-ray absorption fine structure (NEXAFS) spectroscopy measurements. XRD results indicate that films exhibit single phase nature with rutile structure and exclude the secondary phase related to Mn metal cluster or any oxide phase of Mn. Magnetization studies reveal that both the films (3% and 5% Mn doped TiO2) exhibit room temperature ferromagnetism and saturation magnetization increases with increase in concentration of Mn doping. The spectral features of XMCD at Mn L3,2 edge show that Mn2+ ions contribute to the ferromagnetism. NEXAFS spectra measured at O K edge show a strong hybridization between Mn, Ti 3d and O 2p orbitals. NEXAFS spectra measured at Mn and Ti L3,2 edge show that Mn exist in +2 valence state, whereas, Ti is in +4 state in Mn doped TiO2 films.Highlights► We have synthesized single phase Mn doped TiO2 thin films using PLD technique. ► XRD results indicate that films exhibit single phase nature with rutile structure and exclude the secondary phase. ► Field cooled magnetization and magnetic hysteresis loop studies infer that Mn doped TiO2 films show room temperature ferromagnetism. ► XMCD measurements at Mn L3,2 edge show that Mn2+ ions contribute to the ferromagnetism. ► NEXAFS spectra measured at Mn and Ti L3,2 edge show that Mn exist in +2 valence state, whereas, Ti is in +4 state in Mn doped TiO2 films.
    Applied Surface Science 01/2011; 257(24):10557-10561. · 2.54 Impact Factor
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    ABSTRACT: The electromagnetic properties and microstructures of a Cu75–Fe5–Ni20 alloy have been investigated on isothermal annealing at 1073 K, using a superconducting quantum interference device magnetometer, quantum design, physical property measurement system and transmission electron microscopy. Nanoscale magnetic particles were formed randomly in the Cu-rich matrix after receiving a short annealing due to the phase decomposition in the alloy. With increasing isothermal annealing time, however, rod-type precipitates aligned along the 1 0 0 directions were observed in the matrix, on isothermal annealing at 1073 K. Although the size of the precipitates became larger (from ~10 nm to >300 nm) after further annealing, no significant change (less than 2%) was detected in the MR value. The largest MR value (MR ~16% at H = 7 T and T = 10 K) was attained, in particular, for the as-quenched specimen. This study revealed that several significant influences were introduced into the magnetic and magnetoresistive properties during the phase decomposition process in the Cu–Fe–Ni alloy.
    Journal of Physics D Applied Physics 09/2010; 43(41):415001. · 2.53 Impact Factor
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    ABSTRACT: In this study, the magnetic and the magnetocaloric properties of the La0.66Sr0.34MnO3 (LSMO) compound were investigated. The X-ray diffraction result indicates that the LSMO sample has a single phase of rhombohedral symmetry without any impurity phase. The magnetic study reveals that the specimen La0.66Sr0.34MnO3 exhibits a ferromagnetic-paramagnetic transition at T C ∼ 376 K. Using Arrott plots, the phase transition from ferromagnetic to paramagnetic is found to be of second order. A maximum magnetic entropy change of 1.25 J/kgK has been observed for a low applied magnetic field of 1T. The relative cooling power values exhibit a nearly linear dependence on the applied magnetic field. Moreover, the analysis of the magnetocaloric effect (MCE) using the Landau theory o f phase transitions shows good agreement with the experimental results, confirming the importance of magnetoelastic coupling and electron interactions in the magnetocaloric properties of perovskite manganites. This investigation suggests that La0.66Sr0.34MnO3 can be used as a potential magnetic refrigeration material.
    Journal- Korean Physical Society 60(10). · 0.51 Impact Factor
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    ABSTRACT: The magnetocaloric properties of new complex magnetic material La0.65Sr0.35Cu0.1Mn0.9O3, suitable for the Ericsson cycle, have been investigated. For this material, the effect of Cu doping can be attributed to a combination of doping disorder, Cu-Mn super exchange interactions and a site-percolation mechanism, which suppress the metallic conduction and Curie temperature. The Curie temperature decreases to 355 K. The magnetocaloric study exposes a comparable value of the magnetic entropy change for La0.65Sr0.35Cu0.1Mn0.9O3 sample, the value of the maximum entropy change, increases from 1.132 J/kgK to 3.11 J/kgK as magnetic field increases from 1 T to 4 T. A large relative cooling power (RCP) has been observed for La0.65Sr0.35Cu0.1Mn0.9O3. As a result, the studied sample can be considered as potential material for magnetic refrigeration.
    Journal of Electroceramics 30(1-2). · 1.14 Impact Factor