Observation of the vortex-glass and the melting transitions in NdBa2Cu3O7-y single crystals grown by different methods

Abstract

We present the transport and magnetization properties of NBCO single crystals grown by the travelling solvent floating zone (TSFZ) and the self-flux (SF) methods under low O2 partial pressure. The TSFZ-grown crystal shows a continuous transition exhibiting a vortex-glass behaviour in V-I characteristics for H = 1 T. In contrast, a first-order melting transition was observed in the crystal grown by the SF method under 0.03% O2 partial pressure displaying a kink and hysteresis in resistance. The temperature dependent magnetization curves show a change in slope at the melting transition. The V-I characteristics in field for the SF-grown crystal exhibited a characteristic S-shape behaviour at the melting transition. The different behaviour in transport properties between two set of crystals suggests that the presence of twin planes and the substitutional defects play a major role in the observed vortex dynamics.