• Title/Summary/Keyword: magnetic transition

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Research Trend of Metal-Organic Frameworks for Magnetic Refrigeration Materials Application (자기 냉동 재료 응용을 위한 MOF의 연구 동향)

  • Kim, Suhwan;Son, Kwanghyo;Oh, Hyunchul
    • Korean Journal of Materials Research
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    • v.30 no.3
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    • pp.136-141
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    • 2020
  • The magnetocaloric effect (MCE), which is the reversible temperature change of magnetic materials due to an applied magnetic field, occurs largely in the vicinity of the magnetic phase transition temperature. This phenomenon can be used to induce magnetic refrigeration, a viable, energy-efficient solid-state cooling technology. Recently, Metal-organic frameworks (MOFs), due to their structural diversity of tunable crystalline pore structure and chemical functionality, have been studied as good candidates for magnetic refrigeration materials in the cryogenic region. In cryogenic cooling applications, MCE using MOF can have great potential, and is even considered comparable to conventional lanthanum alloys and magnetic nanoparticles. Owing to the presence of large internal pores, however, MOF also exhibits the drawback of low magnetic density. To overcome this problem, therefore, recent reports in literature that achieve high magnetic entropy change using a dense structure formation and ligand tuning are introduced.

Velocity Oscillations in the Chromosphere and the Transition Region above Plage Regions

  • Kwak, Hannah;Chae, Jongchul
    • The Bulletin of The Korean Astronomical Society
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    • v.42 no.2
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    • pp.81.4-82
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    • 2017
  • We investigate velocity oscillations in the active region plage by using the high-spatial, high-spectral and high-temporal resolution spectral data acquired by the Interface Region Imaging Spectrograph (IRIS). From the Mn I $2801.907{\AA}$ (lower chromosphere), C II (lower transition region) and Si IV (middle transition region) lines, we measure the line of sight Doppler velocity at different atmospheric layers, and present results of wavelet analysis of the plage region with a range of periods from 2 to 8 minutes. In addition, we present correlations of the oscillations from the lower chromosphere to the middle transition region. Finally, we will discuss the regional dependence of the oscillation properties on physical properties such as temperature and magnetic field inclination.

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Magnetoconductance of a Hybrid Quantum Ring: Effects of Antidot Potentials

  • Kim, Nammee;Park, Dae-Han;Kim, Heesang
    • Proceedings of the Korean Vacuum Society Conference
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    • 2016.02a
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    • pp.335.1-335.1
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    • 2016
  • The electronic structures of a hybrid magnetic-electric quantum ring and two terminal conductance taking into account the resonant backscattering via both magnetic and electric edge channels are studied. The hybrid magnetic-electric quantum ring is formed by a magnetic quantum dot combined with an additional antidot electrostatic potential at the center of the dot. Electrons are both magnetically and electrically confined to the plane. The antidot potential repelling electrons from the center of the dot plays an important role in the energy spectra and magnetoconductance. The angular momentum transition in the ground state and the behavior of magnetoconductance due to a change of the antidot potential are shown in comparison with the conventional magnetic quantum dot.

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Magnetic Properties of SrRuO3 Thin Films Having Different Crystal Symmetries

  • Kim, Jin-I;Jung, C.U.
    • Journal of Magnetics
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    • v.13 no.2
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    • pp.57-60
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    • 2008
  • This study examined the effect of various types of epitaxial strain on the magnetic properties of $SrRuO_3$ thin films. Epitaxial $SrTiO_3$ (001), $SrTiO_3$ (110), and $SrTiO_3$ (111) substrates were used to apply different crystal symmetries to the grown films. The films were grown using pulsed laser deposition. The X-ray diffraction patterns of the films grown under optimum conditions showed very clear peaks for the $SrRuO_3$ film and $SrTiO_3$ substrates. The saturated magnetic moment at 5 K after 7 Tesla field cooling was $1.2-1.4\;{\mu}_B$/Ru. The magnetic easy axis for all three types of films was along the surface normal. The magnetic transition temperature for the $SrRuO_3$ film with lower symmetry was slightly larger than the $SrRuO_3$ film with higher symmetry.

Experimental Study for Ferrofluid Couette Flow between Two Coaxial Spheres (동축 구 사이의 자성 유체의 Couette 유동에 관한 연구)

  • 구도연;하옥남;전운학
    • Transactions of the Korean Society of Automotive Engineers
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    • v.4 no.3
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    • pp.1-9
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    • 1996
  • This study investigated torque characteristics for Couette flow experimentally under circumstaces that ferrofluids were between two coaxial spheres. Torque measurement was obtained for the situation where the inner sphere was rotating while the outer sphere was kept stationary. The magnetic field was imposed on the fluid, using a bar magnet which was inserted in the inner sphere. In the laminar flow region the torque increase when the magnetic field is applied and the critical Reynolds number is increased. However, in the transition regime, the effect of the magnetic field on the torque characteristics decrease as Reynolds number increases. The value of torque were the same as those of glycerine solution beyond the cirtical Reynolds number. We also made experimental equation which could obtain coefficient of torque within critical Reynolds number in terms of sphere spacing Reynolds number and magnetic properties of ferrofluid.

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SPIN REORIENTATION TRANSIT10N OF ULTRATHIN Co FILMS ON ARTIFICIALLY ROUGHENED Pd(111) SINGLE CRYSTAL (블록 공중합체를 이용한 CoCrPt 나노점 배열의 자기적 성질 연구)

  • Jeong, Jong-Ryul;Park, Yong-Sung;Kim, Jong-Hyun;Lee, Jeong-Won;Shin, Sung-Chul
    • Proceedings of the Korean Magnestics Society Conference
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    • 2002.12a
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    • pp.78-79
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    • 2002
  • It is well known that surface and interface roughnesses greatly affect the magnetic properties such as magnetic domain structure, magnetization reversal, magnetoresistance, and spin reorientation transition (SRT) of ultrathin magnetic films. Therefore, recent studies focus on artificially roughened surface, since it could be possible to systematically understand the effect of roughness on the magnetic properties as well as to obtain the desirable magnetic properties by artificially creating the surface structure and morphology. (omitted)

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Ordering of manganese spins in photoconducting $Zn_{1-x}Mn_xTe$

  • Kajitani, T.;Kamiya, T.;Sato, K.;Shamoto, S.;Ono, Y.;Sato, T.;Oka, Y.
    • Proceedings of the Korea Association of Crystal Growth Conference
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    • 1998.06a
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    • pp.39-43
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    • 1998
  • Single crystals of{{{{ { Zn}_{ 1-x} {Mn }_{x }{Te} }}}} with x=0.3-0.6 were prepared by the standard Bridgeman method. Diffuse neutron diffraction intensities due to the short range magnetic ordering is found in the vicinities of 1 1/2 0 reciprocal point and its equivalent point, indicating that the magnetic correlation of the clusters is the type III antiferromangetic one do the F-type Bravais class crystals, being identical with that of {{{{{ Cd}_{ 1-x} {Mn }_{x }Te }}}}. Neutron inelastic scattering measure-ment has been performed for {{{{{ Zn}_{ 0.6} { Mn}_{ 0.4}Te }}}} sample using the cold neutron spectrometer. AGNES. High resolution measurement with the energy resolution of {{{{ TRIANGLE E= +- .01meV}}}} was carried out in the temperature range from 10K to the ambient. Critical scattering, closely related with the spin glass transition, has been observed for the first time in this semimagnetic semi-conductor. The critical scattering is observed at temperatures in the vicinity of the spin glass transition temperature, 17K. The scattering is observed as a kind of quasielastic scattering in the reciprocal range where the elastic magnetic diffuse scattering has been observed, e.g., 11/20 reciprocal point, indicating the spin fluctuation has dynamic components in this material. Photoconductivity has been discovered below 150K in {{{{{ Zn}_{ 0.4} {Mn }_{0.6 } Te}}}}. The electric AC conductivity has been increased dramatically under the laser light with the wave lengths of {{{{ lambda =6328,5145 and4880 }}}}$\AA$ ,respectively. After the light was darkened, the conductivity was reduced to the original level after about 2000 seconds at 50K, being above the spin glass transition temperature. This phenomenon is the typical persistent photoconductivity; PPC which was similarly found in {{{{ { Zn}_{ 1-x} { Mn}_{x} Te}}}}.

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