  Two different approaches to the problem of carrier-induced ferromagnetism in
the system of the disordered magnetic ions, one bases on self-consistent
procedure for the exchange mean fields, other one bases on the RKKY
interaction, used in present literature as the alternative approximations is
analyzed. Our calculations in the framework of exactly solvable model show that
two different contributions to the magnetic characteristics of the system
represent these approaches. One stems from the diagonal part of carrier-ion
exchange interaction that corresponds to mean field approximation. Other one
stems from the off-diagonal part that describes the interaction between ion
spins via free carriers. These two contributions can be responsible for the
different magnetic properties, so aforementioned approaches are complementary,
not alternative. A general approach is proposed and compared with different
approximations to the problem under consideration.
