Irreversibility field above 14 T at 77 K in (Nd--Eu--Gd)Ba2Cu3Oy

In (Nd_0.33Eu_0.38Gd_0.28)Ba₂Cu₃O_y, a new type of nanometer-scale pinning center was created by choosing an appropriate matrix chemical ratio. Such a pinning center could be controlled via externally added small quantity of 211 (NEG-211 or Gd-211) secondary phase. Microstructure analysis combined with magnetic characterization clarified that the sample with a high irreversibility field always exhibits chemical modulation and formation of a special nanometer-scale lamellar structure. High magnification STM observations revealed that the nano-lamellas consist of rows of aligned NEG-rich clusters 3 to 4 nm in size. This new material with the Nd:Eu:Gd ratio of 1:1.25:0.85 combined with 5 mol% 211 secondary phase exhibits the high secondary peak position at around 4.5 T and the irreversibility field over 14 T at 77 K for H_a||c-axis.