| we use the local density approximation ( lda ) and lda+u schemes to study the magnetism of ( gamn)as and ( gamn)n for a number of mn concentrations and varying number of holes . we show that for both systems and both calculational schemes the presence of holes is crucial for establishing ferromagnetism . for both systems , the introduction of @xmath0 increases delocalization of the holes and , simultaneously , decreases the p - d interaction . since these two trends exert opposite influences on the mn - mn exchange interaction the character of the variation of the curie temperature ( t@xmath1 ) can not be predicted without direct calculation . we show that the variation of t@xmath1 is different for two systems . for low mn concentrations we obtain the tendency to increasing t@xmath1 in the case of ( gamn)n whereas an opposite tendency to decreasing t@xmath1 is obtained for ( gamn)as . we reveal the origin of this difference by inspecting the properties of the densities of states and holes for both systems . the main body of calculations is performed within a supercell approach . the curie temperatures calculated within the coherent potential approximation to atomic disorder are reported for comparison . both approaches give similar qualitative behavior . the results of calculations are related to the experimental data . |