The effects of density and size of BaMO3 (M=Zr, Nb, Sn) nanoparticles on the vortex glassy and liquid phase in (Y,Gd)Ba2Cu3Oy coated conductors

We studied the effect of systematically-controlled size (22–83 nm) and density (0.1–13 × 1021 m−3) of strong pinning random BaMO3 (M=Zr, Nb, Sn) nanoparticles (NPs) by engineering of their inclusion in (Y0.77Gd0.23)Ba2Cu3Oy ((Y,Gd)BCO) coated conductors. The critical current density (Jc) gradually increases from that of pure (Y,Gd)BCO to that of 3 wt% BZO with increasing density of NPs for H ‖ c and H ‖ 45°. Moreover, at low/intermediate fields the films with higher densities of isotropic pinning centers show nearly isotropic angular dependence at both 77 and 65 K, indicating that a high density of spherical nanoparticles effectively pins vortices over a broad angular range. We find that the enhancement of Jc depends mainly on the density of the NPs and not on their size. The vortex melting transition (characterized by the critical exponent (s) of the resistive transition) changes, particularly at H ‖ 45° in films with higher densities of NPs. This change is reflected in a decrease of s to a value very close to that observed for H ‖ c, similar to that of a Bose-glass. Thus, the density and morphology of the pinning centers are important factors determining not only Jc but also the character of the solid–liquid transition. (paper)