When doping the antiferromagnetically ordered high-T(c) cuprates with
holes magnetic polarons (spin-polarized clusters) are formed. We discu
ss two different mean-field approaches of the three-band Hubbard model
to calculate the binding energy and polarization of the clusters. At
higher hole concentrations and due to cluster diffusion a phase separa
tion is formed by establishing large fractal or percolative clusters.
This percolation picture allows us to understand experimentally obtain
ed results for phase separation as well as magnetic and conductive pha
se diagrams.