Yasuaki Onodera

Publications (3)1.61 Total impact

• Article: Anomalous magnetization due to the vortex lattice melting transition in YBa2Cu3Oy

  Terukazu Nishizaki, Yasuaki Onodera, Tomoyuki Naito, Norio Kobayashi
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  ABSTRACT: Magnetization measurements in YBa2Cu3Oy single crystals are performed as a function of the temperature T and the magnetic field H. It is found that an anomalous magnetization step which provides the thermodynamic evidence of the first-order vortex lattice melting transition and the resistive kink with the hysteresis are observed in the same phase boundary in H-T plane. For samples with a small value of the irreversibility field Hirr(T) as compared with the vortex lattice melting line Hm(T), the vortex lattice melting is observed in the reversible magnetization region and the entropy change per vortex per CuO2 layer at the transition is estimated to be s0.5–1.0 k B . For samples with a slightly larger value of Hirr(T) comparable to Hm(T), on the other hand, the jump height and the value of s is enhanced. Thus, the value of s is affected significantly by the relation between H irr (T) which varies from sample to sample and Hm(T) which is an universal line.
  Journal of Low Temperature Physics 11/1996; 105(5):1183-1188. · 1.19 Impact Factor
• Article: Magnetic phase diagram and vortex pinning in YBa2Cu3O y single crystals

  Terukazu Nishizaki, Yasuaki Onodera, Tomoyuki Naito, Hidehito Asaoka, Humihiko Takei, Norio Kobayashi
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  ABSTRACT: Magnetization measurements in YBa2Cu3O y single crystals are performed as a function of the temperatureT and the magnetic fieldH parallel to thec-axis. We find that the critical current densityJ c shows a sharp peeak just below the vortex lattice melting lineH m(T); the peak ofJ c (T) is enhanced whenH m(T) agrees with the irreversibility lineH irr(T).J c shows largeT dependence below the peak, following the power law dependence ofJ c α (1−t) n withn≈-5.5. The temperature decendence ofJ c is well described by the collective pinning theory using the elemental pinning force for small defects.
  Czechoslovak Journal of Physics 02/1996; 46:1595-1596. · 0.42 Impact Factor
• Article: Magnetization jump and the vortex-lattice melting transition in YBa_ {2} Cu_ {3} O_ {y}

  Terukazu Nishizaki, Yasuaki Onodera, Norio Kobayashi, Hidehito Asaoka, Humihiko Takei
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  ABSTRACT: Magnetization measurements in high-quality twinned YBa2Cu3Oy single crystals are performed as a function of temperature, magnetic field, and its direction. We find an anomalous magnetization jump just below the irreversibility line, which provides the thermodynamic evidence of the first-order vortex-lattice melting transition in YBa2Cu3Oy system, following a reasonable Lindemann criterion with cL=0.13. In addition, we demonstrate that a peak effect in the critical current density just below the melting line is associated with the enhanced vortex pinning due to the premelt softening of the vortex lattice and this peak is different from a so-called second peak.
  Phys. Rev. B. 12/1995; 53(1).