Yuncai Xue

Influence of Gd/Eu Substitution on the Local Electron Density and the Superconductivity of Y1−xRxBa2Cu3O7−δ (R=Gd, Eu) Systems

The influences of Gd or Eu substitution on the local electronic density, lattice structure and the superconductivity are systemically studied by means of positron annihilation technique (PAT) and x‐ray diffraction (XRD) for Y1−xRxBa2Cu3O7−δ (R=Gd, Eu; x=0.0, 0.2, 0.5, 1.0) systems. XRD results show that all of the Y1−xRxBa2Cu3O7−δ samples have an orthorhombic phase as same as YBa2Cu3O7−δ (YBCO) sample. The positron annihilation experiments show that the mean positron lifetime increases with increasing Eu or Gd substitution content. The local electron density ne is evaluated as a function of the substitution content. The results indicate that the substitution ions in Y sites not only influence the local electron density around Y ion, but also change the distribution of electron density around Cu‐O chains. These results prove that the changes of ne, the degree of orthorhombic distortion and the coupling between the Cu‐O chains and the CuO2 planes all have an effect on the superconductivity of Y1−xRxBa2Cu3O7...

Spin Correlated Scattering and Metal‐Semiconductor Transition in CMR Manganites

The CMR manganites are one of the most interesting and widely noticed objects in the physical and materials sciences based on their possible application on CMR properties and sensor technology at low‐temperature, strong correlation characteristic, ordering of spin/charge/orbital including lattice degree of freedom. In this paper, a Kondo‐like transport was observed in the term of a metal‐semiconductor transition at low temperature in this ferromagnetic metallic phase system. The experiments show that this kind of Kondo‐like behavior can be tuned with an applied magnetic field and depends strongly on the content of a spin glass phase, which can be explained by the scattering of spin disorder or/and antiferromagnetic cluster in a micro‐scale. In undoped sample, the M‐SC transition would mean the existence of intrinsic spin disorder with magnetic inhomogeneities and gives a direct evidence of Kondo effect in ferromagnetic metallic manganites. It was also proved that Kondo‐like abnormity appears not only in t...