On the critical fields and current densities of YBa2Cu3O7 and La1.85Sr0.15CuO4 superconductors

Abstract

We report a detailed investigation of the magnetic hysteresis of YBa₂Cu₃O₇ oxide in fields ranging from ∼0.2 Oe to 35 kOe and at different temperatures (4.2≤T≤100 K). It is shown that the magnetic behavior is that of a granular type‐II superconductor in which strongly superconducting grains are coupled via less superconducting links. As a result, at low‐H (H≲20 Oe at 4.2 K) the sample appears like a single superconducting filament while at high enough field (H≳5 kOe) it behaves like a granular superconductor with most of the weak links being broken by the applied field. Five threshold fields are identified charaterizing the above magnetic regimes and the transition between them. It is concluded that the critical current density within the individual grains could attain 10⁷ A/cm².