Ettingshausen and Nernst effects in mixed state of YBa_2Cu_3O_<7-δ>(High Field Superconductors)

概要

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The dissipative behaviors under the Lorentz force and the thermal force are investigated for the same sample of QMG-YBa_2Cu_3O_<7-δ> by measuring the Ettingshausen and the Nernst effects, respectively, and compared with each other. The value of S_φ(T) obtained from the Nernst effect is found to be smaller than that obtained from the Ettingshausen effect, which suggests that the viscosity is not the same for the vortex motions under the Lorentz force and the thermal force. The QMG-YBa_2Cu_3O_<7-δ> always includes precipitates of Y_2BaCuO_5 phase which are finely dispersed by an addition of Pt. In order to investigate the effect of Y_2BaCuO_5 phase on the vortex motion, the Ettingshausen effect is also measured for the sample with 0.5 mass% Pt addition. The anisotropy of the dissipation under the thermal force is investigated by measuring the Nernst effect for the configurations; (1) H//c, (dT/dx)//ab, (2) H//ab, (dT/dr)//ab and (3) H//ab, (dT/dr)//c. For these vortex motions, viscosities are found to be in the ratio 30 : 1 : 100. The velocity of vortices is estimated from the Nernst field. Furthermore, using S_φ(T) the magnitude of viscosity is estimated to be 0.5-3×10^<-7> N s/m^2 in the temperature range from 90 to 75 K and the magnetic field of 13 T parallel to the c-axis.YBa_2Cu_3O_<7-δ>Ettingshausen effectNernst effectvortex motiontransport entropy of a vortex
東北大学の論文
1996-07-15