Dynamic motion of vortices in Bi2Sr2CaCu2O8 single crystal with low
density columnar defects by using a magnetic force microscope. Single
crystal Bi2Sr2CaCu2O8 sample was irradiated by 1.3 GeV uranium ion
to form artificial pinning centers alog the crystalline c-axis. The
irradiation dose corresponded to a matching field of 20 gauss. The
radius of an individual vortex is approximately 140 nm, which is close
to the penetration depth of this material. Magnetic force microscope
(MFM) images show that intrinsic crystalline defects such as
stacking fault dislocations are very effective pinning centers for
vortices in addition to the pinning centers due to ion
bombardment. By counting the number of vortex, we found that the flux
trapped at each pinning center is a single flux quantum. At higher
magnetic field, the vortex structure showed an Abrikosov lattice
disturbed only by immobile vortices located at pinning centers.
When increasing or decreasing the external magnetic field, the
spatial distribution of vortices showed a Bean model like
behavior.