The critical current density (J _c ) of YBa ₂ Cu ₃ O _7-z films doped with varying flux pinning nanoparticle additions was systematically studied, for applied magnetic fields of H = 0-9 T and operation temperatures T = 20-77 K. Films were prepared with pulsed laser deposition by (M/YBCO) _N multilayer or (YBCO) _1-x M _x single-target methods, for different M phases including Y ₂ O ₃ , Y ₂ BaCuO ₅ (Y211) green-phase, and BaZrO ₃ . Very significant differences of J _c (H//c,20-77 K) were measured for optimized M phase additions, that are difficult to model or predict at present. Multilayer films with Y211 and Y ₂ O ₃ nanoparticle additions had the highest J _c (20-77 K) for H < 4 T, and YBCO+BZO-nanorod samples had the strongest J _c (H) for H > 4 T and 65-77 K, however not for T < 50 K. Seemingly unusual J _c (H,T) properties were measured for (BZO/YBCO) _N multilayer films when compared to YBCO and other doped films; J _c (H) was almost the same as YBCO at 77 K, however at 30 K J _c (H > 2 T) had the strongest properties increasing 70% compared to YBCO+nanoaddition films and increasing 400% compared to YBCO.

M. J. Mullins

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