A correlação entre irreversibilidade magnética e resistência elétrica nula em monocristais de YBa2Cu3O7-δ dopados quimicamente

Abstract

At this work is conducted an experimental study of dc magnetometry and ac electrical resistivity about the effects of substitution of Y for Ca up to 10% in YBa 2 Cu 3 O 7-δ structure on the magnetic irreversibility, T (H) and zero electric resistance, T 0 (H) temperatures. The Y 1-x Ca x Ba 2 Cu 3 O 7-δ irr (x = 0, 0,01 e 0,1) single crystals were prepared by self flux technique and the dc magnetization and magnetoresistance measurements were conducted respectively with a SQUID and a PPMS measurement systems. Magnetic fields up to 50kOe were applied parallel to the c axis of single crystals. The magnetoresistance transition of the McCa1% sample displayed a strong inhomogeneous character which was not reproduced to the McCa10% sample. The observation of this particular character to the McCa1% sample was attributed to the possible underdoped oxygen level of its structure. The magnetic irreversibility line (MIL) behavior of doped samples at the H-T diagram was characterized by predominance of the Josephson vortices dynamic to H ≤ 1kOe and to H > 1kOe the MIL was ruled by the Abrikosov vortices dynamic. In this scenario the MIL behavior to H ≤ 1kOe is interpreted by the superconducting glass model take into account the spin glass magnetic irreversibility analogy. In contrast, the MIL behavior to H > 1kOe is described by the giant flux creep (gfc) model. The gfc model was applied to the MIL interpretation of the YBa 2 Cu 3 O (McY) singlecrystal in its H-T diagram entirety. In the doped samples the T 7-δ irr (H) and T (H) correlation has been shown discordant to H ≤ 5kOe. This particular behavior suggests that these temperatures depend of different parts of sample as could be expected to a granular superconductor when the T irr 0 (H) is ruled by the interconnectivity established between the superconducting regions (grains) of the sample and the T (H) is ruled by the percolation of superconducting grains arrays over of cross section area of the sample. In contrast, the T 0 irr (H) and T (H) are identical to H > 5kOe what agrees to Abrikosov vortices dynamics preponderance on the high magnetic field regime.