Remanent magnetization of layered and isotropic superconductors (abstract)

Abstract

There are contradicting data on the anisotropy of remanent magnetization of high-temperature superconductors. To clarify the mechanism of this anisotropy we performed a comparative study of thermoremanent (TRM) and isothermal remanent (IRM) magnetizations. We report on the results obtained on layered single crystals of LaCrSuO and RBaCuO (R=Y,Gd) families as well as on isotropic soft alloy Bi:Pb:Sn and nontextured ceramic YBaCuO samples. The experiments were done by means of a vibrating-sample magnetometer. The external magnetic field up to 8 kOe was applied to magnetize the samples at arbitrary directions. It was found that all the studied plate-like samples show the effect of ‘‘easy remanent magnetization axis:’’ the vectors of IRM and TRM tend to point along the normal of the plate at any magnetizing or cooling angle. In the case of TRM this effect can be well described considering the influence of the sample shape. This fact was proved by measurements on samples with substantially different aspect ratios. Thus, we argue that the anisotropy of TRM is not related to anisotropic flux trapping. The anisotropy of IRM is a more complex phenomenon, as it involves inhomogeneous flux distribution in the sample. Nevertheless, it was found that the dependence of IRM direction on the magnetizing angle is also governed mainly by the sample shape. The corrections to the effective demagnetization factors were calculated, which arise due to the flux distribution. The analysis of the absolute value of IRM on the magnetizing angle allows one to distinguish between the influence of the critical current anisotropy and the sample shape.