  We present an experimental study for polycrystalline samples of the diluted
magnetic semiconductor Mn(x)Ga(1-x)N (x<0.04) in order to address some of the
existing controversial issues. Different techniques were used to characterize
the electronic, magnetic, and structural properties of the samples, and
inelastic neutron scattering was employed to determine the magnetic excitations
associated with Mn monomers and dimers. Our main conclusions are as follows:
(i) The valence of the Mn ions is 2+. (ii) The Mn(2+) ions experience a
substantial single-ion axial anisotropy with parameter D=0.027(3) meV. (iii)
Nearest-neighbor Mn(2+) ions are coupled antiferromagnetically. The exchange
parameter J= 0.140(7) meV is independent of the Mn content x, i.e., there is no
evidence for hole-induced modifications of J towards a potentially high Curie
temperature postulated in the literature.
