• Title/Summary/Keyword: magnetic transition

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The Effect of Cr doping on the Magnetic and Magnetocaloric Properties of MnCoGe Alloys

  • Emre, S. Yuce
    • Journal of Magnetics
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    • v.18 no.4
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    • pp.405-411
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    • 2013
  • The structural, magnetic and magnetocaloric properties of $CoMn_{1-x}Cr_xGe$ (x=0.05-0.125) have been investigated by using electron microscopy, x-ray diffraction, calorimetric and magnetic measurements. In this study, our aim is to justify the magnetocaloric effect by tuning the structural and magnetic transition temperature with Cr doping on CoMnGe pure system. The substitution of Cr for Mn leads to a decrease of both structural and magnetic transition temperatures. However, structural and magnetic transition temperatures do not close to each other. From magnetization measurement, we calculate that isothermal entropy change associated with magnetic transition can be as high as 3.82 J $kg^{-1}K^{-1}$ at 302 K in a field of 7 T. Meanwhile, structural phase transition contribution to isothermal entropy change is calculated as 5.85 J $kg^{-1}K^{-1}$ at 322 K for 7 T.

Magnetic Properties of Transition Metal Monolayers on Ta(001) Surfaces

  • Youn, S.J.;Hong, S.C.
    • Journal of Magnetics
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    • v.13 no.4
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    • pp.140-143
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    • 2008
  • The magnetic and structural properties of transition metal (Mn, Fe, Co) monolayers on Ta(001) surfaces are investigated theoretically by using the first principles full-potential linearized augmented plane wave method. Mn and Fe monolayers become ferromagnetic on Ta(001) surfaces while Co monolayers becomes non-magnetic. The paramagnetism of Co monolayers is explained by the Stoner theory of magnetism. The magnetic coupling of a transition metal overlayer with a substrate is ascribed to the orbital hybridization between the s and d orbitals of the transition metal.

Double Transition and Magnetic Phase Transition : An Electron Fluid Condensation Model for Superconductivity (이중 전이와 자화 상전이 : 초전도성에 대한 전자 유체의 응축 모델)

  • Park, Sung-Hoon;Choi, Dong-Seek;Shin, Doo-Soon;Kim, Won-Soo
    • Journal of the Korean Chemical Society
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    • v.42 no.6
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    • pp.599-606
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    • 1998
  • Since the discovery of ceramic superconductor the various theoretical developments has progressed but there are no definitive description about the superconducting transition mechanism. In special, both the double transition and the various magnetic phase transition add to the complication of the understanding of HTSC. In this paper, we presented the idea of the two-step mechanism for the superconducting transition in view of the condensation model of electron fluid for superconductivity. And these concepts are successfully applied to the double transition and the magnetic phase diagram of various types of superconductivity. Therefore, both the double transition and magnetic phase transition should be the touchstone of general theory for superconductivity.

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The Magnetic Field Dependence of the Confinement Potential due to the Interaction of Electron and Piezoelectric Phonon in GaAs Semiconducting Materials (구속 포텐셜의 전자-압전 포논 상호 작용에 따른 GaAs의 자기장 의존 특성)

  • Lee, Su-Ho;Kim, Hai-Jai;Joo, Seok-Min
    • The Transactions of the Korean Institute of Electrical Engineers P
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    • v.67 no.3
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    • pp.149-154
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    • 2018
  • We consider the system is subject to the linearly polarized oscillatory external field. We study the optical quantum transition Line shapes(QTLS) which show the absorption power and the quantum transition line widths(QTLW) of electron-piezoelectric phonon interacting system. We analyze the magnetic field dependence of the QTLS and the QTLW in various cases. In order to analysis the quantum transition, we compare the magnetic field dependence of the QTLW and the QTLS of two transition process, the intra-Landau level transition process and the inter-Landau level transition process.

Magnetic Properties of Carbon Chains Doped with 4d Transition Metals

  • Jang, Y.R.;Lee, J.I.
    • Journal of Magnetics
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    • v.13 no.1
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    • pp.7-10
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    • 2008
  • The structural and magnetic properties of functionalized carbon chains doped with 4d transition metals, such as Ru, Rh, and Pd, were investigated using the full-potential linearized augmented plane wave (FLAPW) method. The carbon nanowire doped with Ru exhibited a ferromagnetic ground state with a sizable magnetic moment, while those doped with Rh and Pd had nonmagnetic ground states. For the Ru-doped chain, the density of states at the Fermi level showed large spin polarization, which suggests that the doped nanowire could be used for spintronic applications.

Possible Role of Disorder on Magnetostructural Transition in La1-xBaxMnO3

  • Kim, N.G.;Jung, J.H.
    • Journal of Magnetics
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    • v.12 no.3
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    • pp.103-107
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    • 2007
  • Magnetic field induced structural transition has been systematically investigated for $La_{1-x}Ba_xMnO_3$ with the fine control of carrier doping $(0.15{\leq}x{\leq}0.20)$. Application of a magnetic field results in the suppression of the rhombohedral-orthorhombic transition temperature $(T_s)$ and the increase of insulator-metal transition temperature $(T_{MI})$. Near x = 0.17, where $T_S$ is similar to $T_{MI}$ at zero magnetic field, we found that the $T_S$ smoothly decreased with magnetic field even though it intersected the $T_{MI}$ near 3 T. Also, the magnetostructural phase diagram obtained from the temperature sweep and from the magnetic field sweep is not significantly modified. By comparing the magnetostructural transition in $La_{1-x}Sr_xMnO_3$, we have suggested that the large disorder originated from ionic size differences between La and Ba may weaken the sensitivity of the kinetic energy of $e_g$ electrons on the degree of lattice distortion in $La_{1-x}Ba_xMnO_3$.

The Magnetic Field Dependence Properties of Quasi Two Dimensional Electron-piezoelectric Potential Interacting System in GaN and ZnO

  • Lee, S.H.;Sug, J.Y.;Lee, J.H.;Lee, J.T.
    • Journal of Magnetics
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    • v.16 no.4
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    • pp.408-412
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    • 2011
  • We investigated theoretically the magnetic field dependence of the quantum optical transition of qusi 2-Dimensional Landau splitting system, in GaN and ZnO. We apply the Quantum Transport theory (QTR) to the system in the confinement of electrons by square well confinement potential. We use the projected Liouville equation method with Equilibrium Average Projection Scheme (EAPS). Through the analysis of this work, we found the increasing properties of the optical Quantum Transition Line Shapes(QTLSs) which show the absorption power and the Quantum Transition Line Widths(QTLWs) with the magnetic-field in GaN and ZnO. We also found that QTLW, ${\gamma}(B)_{total}$ of GaN < ${\gamma}(B)_{total}$ of ZnO in the magnetic field region B < 25 Tesla.

Width-Dependent Transition of Magnetic Domain Configuration in Nanostructured CoFe/Pt Multilayered Nanowires

  • Je, Soong-Geun;Lee, Jae-Chul;Kim, Kab-Jin;Min, Byoung-Chul;Shin, Kyung-Ho;Choe, Sug-Bong
    • Journal of Magnetics
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    • v.17 no.4
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    • pp.242-244
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    • 2012
  • We report on the basis of experiments that magnetic domain structures exhibit a transition between single and dendrite domains with respect to the width of ferromagnetic nanowires. This transition is directly observed in CoFe/Pt multilayered nanowires having a width in the range of 580 nm to 4.2 ${\mu}m$ with a magnetic force microscope. Nanowires wider than 1.5 ${\mu}m$ show typical dendrite domain patterns, whereas the nanowires narrower than 690 nm exhibit single domain patterns. The transition occurs gradually between these widths, which are similar to the typical widths of the dendrite domains. Such a transition affects the strength of the domain wall propagation field; this finding was made by using a time-resolved magneto-optical Kerr effect microscope, and shows that the domain wall dynamics also exhibit a transition in accordance with the domain configuration.

Formation of Charged Exciton in GaAs-AlGaAs Double-Quantum-Well Structure at High Magnetic Field (GaAs 이중 양자우물구조에서 고자기장에 유도된 대전된 엑시톤의 발생)

  • Kim, Yong Min
    • Journal of Integrative Natural Science
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    • v.2 no.4
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    • pp.265-269
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    • 2009
  • The photoluminescence was measured in GaAs-AlGaAs double-quantum-well structure at high magnetic field. Although the phototransition characteristics displayed a free-particle transition at low magnetic field, the change of free-particle transition into bound-exciton transition was observed at high magnetic field (above 10 T). A charged exciton formation due to charge-unbalanced electron-hole was identified by using a spin-polarized photoluminescence method. An increase of exciton formation due to the localization of free-particle at magnetic field was observed according to the increase of magnetic field.

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Paraelectric-Ferroelectric Phase Transition of (NH4)2SO4 Single Crystals by 14N NMR

  • Lim, Ae Ran
    • Journal of the Korean Magnetic Resonance Society
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    • v.21 no.2
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    • pp.63-66
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    • 2017
  • The $^{14}N$ NMR spectra for $(NH_4)_2SO_4$ crystals were obtained near the phase transition temperature $T_C=223K$, and were found to precisely reflect the symmetry change in the crystal at this first-order phase transition. Changes in the resonance frequencies near $T_C$ were attributed to the structural phase transition. In the ferroelectric and paraelectric phases, two inequivalent NH4 groups were distinguished in the $^{14}N$ NMR spectra. The two types, $NH_4$(1) and $NH_4$(2), have slightly different local environments. Consequently, we conclude that the phase transition is caused by the change in the environment of the $^{14}N$ nuclei in the $NH_4$ groups, rather than by the $SO_4$ groups.