  We grew needle-shaped single crystals of GdAgGe, which crystallizes in a
noncentrosymmetric hexagonal crystal structure with space group
P$\overline{6}$2$m$ (189). The magnetic susceptibility data for $H \perp c$
reveal two pronounced antiferromagnetic transitions at $T_{N1}$ = 20 K and
$T_{N2}$ = 14.5 K. The magnetic susceptibility anomalies are less prominent for
$H \parallel c$. The transition at $T_{N1}$ is accompanied by a pronounced heat
capacity anomaly confirming the bulk nature of the magnetic transition. Below
$T_{N1}$, the electrical resistivity data follows a $T^{3/2}$ dependence. In
the magnetically ordered state, GdAgGe shows positive transverse
magnetoresistance, which increases with decreasing temperature and increasing
field, reaching a value of $\sim$ 27% at 9 T and 10 K. The Hall resistivity
data and electronic band structure calculations suggest that both the hole and
electron charge carriers contribute to the transport properties. The electronic
band structure displays linear band crossings near the Fermi level. The
calculations reveal that GdAgGe has a nodal line with drumhead surface states
coupled with a nonzero Berry phase, making it a nontrivial nodal-line
semimetal.
