Abstract
Experimental results on non-heat-treated (NHT) samples with CuNi matrix, whose filament diameter df ranges from 0.061 to 0.314μm, are given. In case of 4.2K, Jc values at low fields are very different among samples. As df decreases to below 0.1μm, the Jc surprisingly increases and exceeds 1×106A/cm2 at 2T. However, samples which have high Jc values at low fields show a large decrease in Jc with magnetic field. A rise in temperature causes a marked decrease in Jc, especially, for samples with finer filaments. An anomalous change in Jc around 0.1T was also seen at temperatures close to Tc for the sample with df=0.314μm. The reduced pinning curves (Fp/Fp, max vs. B/Bc2) of each sample at various temperatures coincide with each other. Values of reduced field bm indicating the position of Fp, max are lower, 0.15-0.2. The highest value of Fp, max was obtained for a sample with df=0.072μm. Its pinning exponents p and q expressed in the form of Fp={Bc2}nbp(1-b)q are ≈0.5 and ≈2.5, respectively, The critical current density and the pinning properties of these samples are compared to those of heat-treated samples.
