  Magnetic Doppler imaging from four Stokes parameter observations has
uncovered a new level of complexity of stellar magnetic fields previously not
known. This new information is of interest to the evolution and structure of
magnetic fields of intermediate and high-mass stars.
  Recently, we performed magnetic Doppler imaging study of the chemically
peculiar star HD 24712 using phase-resolved spectropolarimetric observations of
line-profiles in all four Stokes parameters. The observations were obtained
with the HARPSpol instrument on the 3.6-m ESO telescope. Our analysis shows
that the magnetic field of HD 24712 has very strong dipolar component with weak
small-scale contributions.
  The finding of dipole-like field for HD 24712 gives evidence for the
hypothesis that old Ap stars have predominantly dipolar magnetic fields. We
plan on performing magnetic Doppler imaging from four Stokes parameter
observations for other Ap/Bp stars as well, which will help us understand the
nature of magnetic fields in these stars.
