  The synthesis and crystallographic and physical properties of polycrystalline
EuNiGe3 are reported. EuNiGe3 crystallizes in the noncentrosymmetric
body-centered tetragonal BaNiSn3-type structure. The physical property data
consistently demonstrate that this is a metallic system in which Eu spins S =
7/2 order antiferromagnetically at a temperature TN = 13.6 K. Magnetic
susceptibility chi data for T > TN indicate that the Eu atoms have spin 7/2
with g = 2, that the Ni atoms are nonmagnetic, and that the dominant
interactions between the Eu spins are ferromagnetic. Thus we propose that
EuNiGe3 has a collinear A-type antiferromagnetic structure. A fit of chi(T <
TN) by our molecular field theory is consistent with a collinear magnetic
structure. Electrical resistivity rho data from TN to 350 K are fitted by the
Bloch-Gruneisen model for electron-phonon scattering, yielding a Debye
temperature of 265(2) K. A strong decrease in rho occurs below TN due to loss
of spin-disorder scattering. Heat capacity data at 25 K < T < 300 K are fitted
by the Debye model, yielding the same Debye temperature 268(2) K as found from
rho(T). The extracted magnetic heat capacity is consistent with S = 7/2. The
magnetic entropy at TN = 13.6 K is 83% of the expected asymptotic high-T value,
with the remainder recovered by 30 K.
