An inductive methodology simultaneously enabling the determination of grain- and intergrain critical current densities of YBa2Cu3O7−x coated conductors is developed. This noninvasive method is based on the identification of a clear peak in the reverse branch of the magnetization loop at a positive magnetic field, as a signature of the electromagnetic granularity inherent to these materials. A quantitative evaluation of the return magnetic field at the grain boundaries allows us to understand the existence of this magnetization peak and quantify the grain critical current density. This methodology is envisaged to sort out granularity effects from vortex pinning effects on coated conductors.

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The structural state and static and dynamic magnetic properties of TbCu2 nanoparticles are reported. The nanoparticles were produced by mechanical milling under inert atmosphere with low milling times ≤ 15 hours. The randomly dispersed nanoparticles as detected by TEM retain the bulk symmetry with an orthorhombic Imma lattice and Tb and Cu in 4c positions. Rietveld refinements confirm that the milling produces a controlled reduction of particle sizes reaching down to ≃ 6 nm and an increase of the microstrain ≃ 0.6 %. The DC-susceptibility shows a reduction of the Néel transition (from 49 K to 43 K) and a progressive increase of the spin glass peak (from 9 to 15 K) in the zero field cooled magnetization with size reduction. The exchange anisotropy is very weak (bias field of ≃ 30 Oe) and is due to the presence of a disordered (thin) shell coupled to the antiferromagnetic core. The dynamic susceptibility evidences a critical slowing down in the spin disordered state with a tendency to increase of zv and β exponents when the size becomes smaller (zv ≃ 6.6 and β ≃ 0.85). A Rietveld analysis of neutron diffraction patterns 1.8 ≤ T ≤ 60 K including the magnetic structure determination reveals that there is a reduction of the expected moment (≃ 80 %) which must be connected to the presence of the disordered particle shell. The core magnetic structure retains the bulk antiferromagnetic arrangement. The overall interpretation is based on a superantiferromagnetic behavior which at low temperatures coexists with a canting of surface moments. We propose a novel magnetic phase diagram as a function of the particle size.

An unusual 4f-superantiferromagnetic state characterized by simultaneous antiferromagnetic and spin-glass behaviors induced by particle-size reduction is revealed in metallic nanoparticles (≈9 nm) of TbCu 2. The Néel temperature is 46 K and the glassy freezing is below ≈9 K and governed by a critical slowing down process. Neutron diffraction at 1.8 K establishes the superantiferromagnetism. The latter is settled by the nanoparticle moments and the freezing mechanism is provided by the surface spins.

Compared with mono-rare earth 123 films, ternary rare earth (Nd,Eu,Gd)Ba2Cu3O7−δ (NEG123) films show higher critical current density (Jc) and improved irreversibility field (Hirr), but no increase in the characteristic field corresponding to a crossover from a low-field plateau to a linear region in a log Jc–log H plot. At intermediate fields, Jc vs H scales as H(−0.5±0.05) for NEG123, in contrast to H(−0.73±0.05) for mono-rare earth samples such as Gd123. The slow power decay of Jc vs H together with the improved Jc and Hirr strongly implies that extra flux pinning centers exist in NEG123, which are thought to be noncorrelated stress fields induced by lattice mismatch.