Flux motion and isotropic effects in MgB2 near the critical temperature
Abant Izzet Baysal University, Department of Physics,
Turgut Gulez Research Laboratory, 14280
a e-mail: email@example.com
Published online: 22 November 2012
The anisotropic behaviour of polycrystalline MgB2 was studied in details by means of angle dependent magnetovoltage measurements (V-θ curves) at the temperatures near the critical temperature Tc, where θ is the angle between the external magnetic field H and the transport current I. The measurement of V-θ curves was carried out at fixed temperatures below Tc for different values of H and I in a range of θ = −20°–200°. Magnetovoltage measurements (V-H curves) were performed for perpendicular and parallel orientations of H with respect to I, i.e., the V⊥-H curves for and V∥-H curves for . The analysis of V-θ curves does not give any agreement with V(θ) ~ sin2(θ) or any modified angular relationship, so that the measured dissipation is nearly independent of the angle between H and I. The isotropic effects observed in MgB2 were discussed in the frame of the continuum approximation, the discrete case and the flux line cutting associated with the double critical state model derived in the literature. Finally, it is concluded that structural disorder induced isotropic effects can explain the isotropic angular dissipation observed in V-θ, I-V and V-H curves.
Key words: Solid State and Materials
© EDP Sciences, Società Italiana di Fisica and Springer-Verlag, 2012