We report on a new type of correlated nanometer-scale pinning structure observed in a melt-processed (Nd0.33Eu0.38Gd0.28)Ba(2)Cu(3)O(y) (NEG-123). It consists of NEG/Ba-rich clusters in the stoichiometric NEG-123 matrix forming a lamellar array with a period of a few nanometers. These lamellas appear within regular twins, thus representing their fine substructure-sometimes straight, sometimes wavy. This new material structure correlates well with the significant enhancement of pinning at high fields, represented by irreversibility field above 14 T at 77 K (B parallel c). We believe that the new pinning medium enables one to significantly broaden the limits for high-field applications.
The addition of long-term Zr 2 O 3 -ball milled Gd 2 BaCuO 5 particles to a standard (Nd,Eu,Gd)Ba 2 Cu 3 O y superconductor led to a spontaneous formation of extremely small ͑20-50 nm͒ Zr-rich ͑Nd,Eu,Gd͒-Ba-Cu-O particles during the melt-growth process. This pinning medium, approaching the interesting physical limit of point-like pins from the side of large normal ones, dramatically enhanced supercurrents up to 90 K, both in low and intermediate fields. As a result, levitation experiment could be performed with liquid oxygen as a coolant. The particle size effect resemblance with fast neutron irradiation of RE-Ba-Cu-O single crystals is discussed.
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