Magnetostriction of several high-T c superconductors

We report on magnetostriction measurements of superconducting and nonsuperconducting YBa2Cu3O7−δ and of two Bi samples with the nominal compositions Bi2CaSr2Cu2O x and Bi0.8Pb0.2Sr0.8CaCu1.5O x . Both types of high temperature superconductors show a nearly identical strongly hysteretic field dependence of the magnetostriction (MS) (Δl/l∼+(2–6)*10−6 at 5 T and 1.5 K). In both cases the MS is a linear function of field in the region 1–5 T, which we explain by striction due to surface currents. Between 1.5 and 35 K the hysteresis of the MS decreases strongly with increasing temperature, which implies a decrease of the pinning force. The MS of quenched nonsuperconducting YBa2Cu3O7−δ is at least two orders of magnitude smaller than that of the superconductor.