We report on a new type of correlated nanometer-scale pinning structure observed in a melt-processed [Formula presented] (NEG-123). It consists of [Formula presented]-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 ([Formula presented]). We believe that the new pinning medium enables one to significantly broaden the limits for high-field applications.
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