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We report on drastic change of vortex dynamics with increase of quenched disorder: for rather weak disorder we found a single vortex creep regime, which we attribute to a Bragg-glass phase, while for enhanced disorder we found an increase of both the depinning current and activation energy with magnetic field, which we attribute to entangled vortex phase. We also found that introduction of additional defects always increases the depinning current, but it increases activation energy only for elastic vortex creep, while it decreases activation energy for plastic vortex creep.PACS numbers: 74.60. Jg, 74.60.Ge, 74.60.Ec, 74.72.Bk The effect of random pinning on crystalline order and on dynamics of the flux-line-lattice (FLL) was a subject of numerous experimental and theoretical investigations. . The field H on was interpreted as a phase boundary between low field ordered and high field disordered vortex phases. These experimental results are supported by theoretical studies. It was shown that in presence of rather weak disorder the FLL retains a quasilong-range order resulting in the so-called Bragg glass phase [4]. However, with the increase of random pinning or magnetic field a transition to strongly disordered entangled vortex phase (glass phase) is predicted [5,6]. A sharp increase in magnetization below the fish-tail peak position H p was observed in N d 1.85 Ce 0.15 CuO 4−d [7] and non twinned YBa 2 Cu 3 O 7−δ [8] single crystals.Magnetic measurements showed that in optimally doped YBa 2 Cu 3 O 7−δ crystals no fishtail behavior is observed both in detwinned [9] and twinned [10] samples, while decrease of the oxygen content always induced non monotonous J m (H)-curves. Two distinctive peculiarities in the magnetization curves of oxygen deficient [10] and electron irradiated [11] crystals were observed: (1) the peaks H on and H p shift toward lower magnetic fields with increasing defect concentration, and (2) in magnetic fields H < H p the current J m increases, while in magnetic fields H > H p the current J m decreases with increasing defect concentration. It is believed [12,13] that the peak H p separates elastic vortex creep in low and plastic vortex creep, mediated by motion of the FLL dislocations, in high magnetic fields. Thus the introduction of additional defects leads to an increase of vortex pinning in the region of elastic creep and such behavior is expected. On the other hand, decrease of pinning force with increasing disorder observed in the region of plastic creep is non trivial, and reasons of such behavior are not known. The aim of this paper is to show the effect of point-like defects concentration on vortex dynamics and pinning parameters in YBa 2 Cu 3 O 7−δ single crystals.The investigated sample was YBa 2 Cu 3 O 7−δ single crystal with T c ≈ 93.5 K and ∆T c < 0.5 K. Twin planes (TP's) inside the measured part of the sample were aligned in one direction. The transport current was applied along the ab-plane and at an angle α = 45 • with respect to TP's. Measurements were performed in magnet...

For pt.I see ibid., vol.4, p.10199 (1992). The recovery of short-range ordered Ni(Al) and Ni(Al,Ti) solid solutions and long-range-ordered Ni3Al intermetallic compounds was investigated by residual electrical resistivity measurements as a function of composition and of fluence, after low-temperature (4-9 K) irradiation with 2.95 MeV electrons. In the solid solutions, long-range defect migration resulted in increases of local order, self-interstitials were found to be mobile above 110 K (at least in the binary alloys) and vacancies to be mobile above 330 K. The recovery spectrum of irradiated intermetallic compounds showed some similarity with that of pure nickel, with a smaller amount of fine structure. The mobility of self-interstitials (corresponding mainly to Ni-Ni dumbbells) occurs at a higher temperature (75 K) than in nickel (50 K) and does not induce significant ordering. By contrast, the Ni vacancies, which are the dominant vacancy species, are slightly less mobile than in nickel and promote some increase of long-range order.

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