Temperature dependence and mechanisms for vortex pinning by periodic arrays of Ni dots in Nb films

Pinning interactions between superconducting vortices in Nb and magnetic Ni dots were studied as a function of current and temperature to clarify the nature of pinning mechanisms. A strong current dependence is found for a square array of dots, with a temperature dependent optimum current for the observation of periodic pinning, that decreases with temperature as (1-T/Tc)3/2. This same temperature dependence is found for the critical current at the first matching field with a rectangular array of dots. The analysis of these results allows to narrow the possible pinning mechanisms to a combination of two: the interaction between the vortex and the magnetic moment of the dot and the proximity effect. Moreover, for the rectangular dot array, the temperature dependence of the crossover between the low field regime with a rectangular vortex lattice to the high field regime with a square configuration has been studied. It is found that the crossover field increases with decreasing temperature. This dependence indicates a change in the balance between elastic and pinning energies, associated with dynamical effects of the vortex lattice in the high field range.Comment: 12 text pages (revtex), 6 figures (1st jpeg, 2nd-6th postscript) accepted in Physical Review

Towards a Model for Shared Data Abstraction with Performance

ion with Performance 2 by D M Goodeve 3 , S A Dobson 4 , J M Nash, J R Davy, P M Dew, M Kara & C P Wadsworth 5 April 1997 1 The work reported in this paper was supported by the UK Engineering and Physical Sciences Research Council under the project `TallShiP: High-level sharing for parallel programming'. 2 This paper has been submitted for publication in Journal of Parallel and Distributed Computing 3 Now at Department of Computer Science, University of York, York, North Yorkshire, Y01 5DD, UK 4 Well-founded Systems Unit, CLRC Rutherford Appleton Laboratory, Chilton, Didcot, Oxfordshire OX11 0QX, UK 5 Formerly at CLRC Rutherford Appleton Laboratory and now an independent consultant Abstract This paper demonstrates the utility of typed shared data abstractions as an effective high-level means of structuring and coordinating parallel programs. Access to data shared by concurrent processes is expressed through operations of Shared Abstract Data Types (SADTs). SADTs abstr..