Determination of levitation force and pinning properties of (Sm123)(1-x)(Yb211)(x) bulk superconductor depending on Yb211 doping ratio

The vertical force density curves of (Sm123)(1-x)(Yb211)(x) high temperature superconductor (HTS) samples prepared by a melt-powder-melt-growth technique were measured during vertical and lateral traverses in zero field cooling (ZFC) regime for various doping levels (x). It was determined that the maximum vertical force density of the samples increases when the doping level increases and after certain level of the doping the force saturates. The pinning properties, which create attractive force, were enhanced up to a certain Yb211 doping level by introducing locally suppressed superconducting regions. These results indicate that the optimization fabrication conditions and Yb211 doping level should be further investigated for larger dimensional samples to enhance technological applicability. The frozen image model was used to predict the experimentally measured levitation force between a permanent magnet (PM) and the superconductor samples. Various configurations of the PM/HTS force interaction were tested according to the magnet and superconductor size. The doped HTS samples do not show very strong; diamagnetic behavior as the frozen image model predicts. The levitation force behavior regarding the dimensions of the PM and HTS indicates an illustration how the diamagnetic behavior of the superconductor transforms into the flux pinning. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim