Magnetostriction of several high-T c superconductors

We report on magnetostriction measurements of superconducting and nonsuperconducting YBa₂Cu₃O_7– and of two Bi samples with the nominal compositions Bi₂CaSr₂Cu₂O_x and Bi_0.8Pb_0.2Sr_0.8CaCu_1.5O_x. Both types of high temperature superconductors show a nearly identical strongly hysteretic field dependence of the magnetostriction (MS) (l/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 YBa₂Cu₃O_7– is at least two orders of magnitude smaller than that of the superconductor.