  A remarkable progress towards functional ferromagnetic semiconductor
materials for spintronics has been achieved in p-type (Ga,Mn)As. Robust
hole-mediated ferromagnetism has, however, been observed also in other III-V
hosts such as antimonides, GaP or (Al,Ga)As which opens a wide area of
possibilities for optimizing the host composition towards higher ferromagnetic
Curie temperatures. Here we explore theoretically ferromagnetism and Mn
incorporation in Ga(As,P) and (Al,Ga)As ternary hosts. While alloying (Ga,Mn)As
with Al has only a small effect on the Curie temperature we predict a sizable
enhancement of Curie temperatures in the smaller lattice constant Ga(As,P)
hosts. Mn-doped Ga(As,P) is also favorable, as compared to (Al,Ga)As, with
respect to the formation of carrier and moment compensating interstitial Mn
impurities. In (Ga,Mn)(As,P) we find a marked decrease of the partial
concentration of these detrimental impurities with increasing P content.
