  Carrier-induced ferromagnetism is investigated in a diluted ferromagnetic
Kondo lattice model for several ordered impurity arrangements on square and
cubic lattices, allowing for quantitative comparison with different theoretical
pictures. The spin stiffness is found to be optimized with respect to hole
doping concentration, exchange interaction strength, as well as spin dilution
due to a competition involving magnitude of carrier spin polarization and its
oscillation length scale. The ferromagnetic transition temperature determined
within the spin-fluctuation theory is in good agreement with experimental
values for $\rm Ga_{1-x}Mn_xAs$.
