Temperature dependence of vortex flux pinning in melt-textured superconductors

Magnetic properties of melt-textured YBa₂Cu₃O ₇ superconductor are studied at different temperatures from 77 K up to the critical temperature, T_C = 91 K, using vibrating sample magnetometer. Initial magnetization curve is measured from the demagnetized state in an applied magnetic field from 0 to 13.5 kOe, followed by measuring the full hysteresis loop. This procedure is repeated at different temperatures between 77 and 91 K. In all the measurements, the magnetic field was applied along the ab-plane of the sample which is perpendicular to the c-axis. Within the framework of the Bean critical state model, our results show that the maximum pinning forces which are represented by the magnetization remanence at which the internal field is zero are found to decrease with increasing temperature and they obey the empirical scale law ΔM(emu/cm³)= 34 × (1- T/T_c)^1/n, where n ≈ 2.9.