  Exchange bias is a horizontal shift of the hysteresis loop observed for a
ferromagnetic layer in contact with an antiferromagnetic layer. Since exchange
bias is related to the spin structure of the antiferromagnet, for its
fundamental understanding a detailed knowledge of the physics of the
antiferromagnetic layer is inevitable. A model is investigated where domains
are formed in the volume of the AFM stabilized by dilution. These domains
become frozen during the initial cooling procedure carrying a remanent net
magnetization which causes and controls exchange bias. Varying the anisotropy
of the antiferromagnet we find a nontrivial dependence of the exchange bias on
the anisotropy of the antiferromagnet.
