  In this paper, we report the experimental observation of diffraction patterns
in a ferrofluid comprising of Fe3O4 nanoparticles in hexane by a 10 mW He-Ne
laser beam. An external dc magnetic field (0-2 kG) was applied perpendicular to
the beam. The diffraction pattern showed variation at different depths of the
sample in both zero and applied magnetic field. The patterns also exhibit a
change in shape and size as the external field is varied. This effect is
presumably arising due to thermally induced self-diffraction under the
influence of gravity and external magnetic field.
