  According to Ginzburg-Landau theory, it has been generally accepted that the
diamagnetic property decreases after the lower critical field. However, we
found that (Fe, Ti) particle doped MgB2 specimens reveal the Delta H = Delta B
section in the magnetization curves, which are not following the theory. We
present whether this phenomenon appears to be only confined to (Fe, Ti)
particle doped Magnesium diborid superconductor, whether there is a theoretical
basis and why it does not appear in other superconductors. We have understood
that the cause of the Delta H = Delta B section is the pinning phenomenon of
defects in the superconductor and it only occurs in volume defect dominating
superconductors. The width of the Delta H = Delta B section along the number of
defects and Hc2 was estimated assuming that defects are in the ideal state, and
compared with experimental results. We hypothesized that pinned fluxes have to
be picked out from the defect and move into an inside of a superconductor
regardless free energy depth of the defect if the distance between fluxes
pinned at the defect is equal to the one of upper critical field. It is
considered that the reason that this phenomenon has not been reported yet is
the flux jump of the volume defect dominating superconductor. The section means
that the fluxes that have penetrated into a inside of a superconductor in which
volume defects exist are preferentially pinned on them over the entire specimen
before Ginzburg-Landau behavior. If the size of volume defects is uniform in
some extent, the influence of the planar and line defects is small and the flux
jump does not occur, we believe that the section must be observed in any
superconductor. It is because this is one of the basic natures of pinning
phenomenon in the volume defect dominating superconductor.
