We present simulations of flux-gradient-driven superconducting rigid vortices interacting with square and triangular arrays of columnar pinning sites in an increasing external magnetic field. These simulations allow us to relate spatio-temporal microscopic information of the vortex lattice with typically measured macroscopic quantities, such as the magnetization M(H). Near the magnetization matching fields, the flux lattice becomes commensurate with the pins only in certain regions of the sample. Matching fields related to unstable vortex configurations do not produce peaks in M(H). In large systems, different matching fields are present at the same external field forming a terraced flux profile.
Figures (a-d) show the Voronoi (Wigner-Seitz) cell construction indicating
the location of the vortices as they move through the first
matching peak. Larger (smaller) cells correspond to low (high) densities
of flux lines and are indicated in dark (light) shading. The vortices
penetrate the sample at the left and right edges of each figure.
(a) Before the matching peak. (b) Exactly at the matching peak. In
(a) and (b) the vortex lattice is commensurate only near the edges
of the sample, as indicated by the squares. (c) Just past the peak, the
commensurability reaches the center of the sample. (d) Beyond the peak,
the commensurability is destroyed throughout the sample.
Figures (a-b) show vortex configurations at much higher matching fields
in another sample. Vortex arrangements of different orientations
form complex domains of various shapes including (a) islands and (b) stripes.
These unexpected and striking flux domain patterns continuously evolve
as a function of the applied field.
C. Reichhardt, J. Groth, C. J. Olson, Stuart Field, and Franco Nori
Published in Physical Review B, 54 16108 (1996).
Two Java movies are available: a movie of low
matching fields, and a movie of higher matching
The paper's source (RevTeX, PostScript figures tar'ed and gzipped).
A PostScript version of the paper is also available.
Created by: Cynthia Olson
Last modified: 1/5/97