Hot nano-particles in polar or paramagnetic liquids interact as   monopoles
  When neutral nano-particles are heated or cooled in a polar liquid, they will interact with each other as if they carry an electrostatic charge that is proportional to the temperature difference between the particle and the surrounding fluid. The same should hold for paramagnetic liquids, in which case the nano-particles should behave as magnetic monopoles. However, the analogy with electrostatics/magnetostatics is not complete: heated/cooled nano-particles do not move under the influence of an applied field. They should, however, interact as monopoles. 
Daan Frenkel
cond-mat.soft