Dissipation in granular high-temperature superconductors: New approach to describing the magnetoresistance hysteresis and the resistive transition in external magnetic fields

An approach to describing the R(H) magnetoresistance hysteresis in granular high-temperature superconductors and behavior of the R(T) resistive transition in these objects in an external magnetic field is proposed. The dissipation is attributed to the subsystem of intergrain boundaries, which form a Josephson junction network. The approach is based on accounting for the effect of magnetic moments of superconducting grains on the resulting (effective) field in the intergrain medium. The described procedure includes (i) establishing of the degree of magnetic flux crowding in the intergrain medium by comparing the experimental data on the R(H) magnetoresistance hysteresis and magnetization M(H), (ii) determining the effective field B_eff in the intergrain medium as a function of external field H and temperature T with regard to the thermomagnetic prehistory, and (iii) fitting the experimental R(H) and R(T) dependences using the Arrhenius expression R ∼ exp(–E_J/ k_B T), where E_J is the parameter corresponding to the Josephson coupling energy. The fundamental novelty of the proposed approach is the extraction of the functional dependences of E_J on the effective field B_eff in the intergrain medium rather than on the external field H, as was made in many previous works. It is shown that the proposed approach makes it possible to adequately describe both the R(H) hysteretic dependences and R(T) dependences of the Y-Ba-Cu-O high-temperature superconductor samples with different morphologies and critical current densities.