  The study of variation of measured cyclotron lines is of fundamental
importance to understand the physics of the accretion process in magnetized
neutron star systems. We investigate the magnetic field formation, evolution
and distribution for several High- Mass X-ray Binaries (HMXBs). We focus our
attention on the cyclotron lines that have been detected in HMXB classes in
their X-ray spectra. As has been correctly pointed out, several sources show
variation in cyclotron lines, this can result due to the effect of accretion
dynamics, and hence that would reflect the magnetic field characteristics.
Besides, the difference in time scales of variation of accretion rate and
different type of companion can be used to distinguish between magnetized
neutron stars.
