  We present a study of the magnetic properties of the electron doped
manganites Ca1-xYxMnO3 (for 0<=x<=0.25) in the paramagnetic regime. For the
less doped samples (x<=0.1) the magnetic susceptibility, c(T), follows a
Curie-Weiss (CW) law only for T > 450 K and, below this temperature, c^-1(T)
shows a ferrimagnetic-like curvature. We approached the discussion of these
results in terms of a simple mean-field model where double exchange,
approximated by a ferromagnetic Heisenberg-like interaction between Mn3+ and
Mn4+ ions, competes with classical superexchange. For higher levels of doping
(x>=0.15), the CW behaviour is observed down to the magnetic ordering
temperature (Tmo) and a better description of c(T) was obtained by assuming
full delocalization of the eg electrons. In order to explore the degree of
delocalization as a function of T and x, we analyzed the problem through
Montecarlo simulations. Within this picture we found that at high T the
electrons doped are completely delocalized but, when Tmo is approached, they
form magnetic polarons of large spin that cause the observed curvature in
c^-1(T) for x<=0.1.
