  We report the physical properties of GdAuGe single crystals, which were grown
using Bi flux. The powder x-ray diffraction data shows that the compound
crystallizes in hexagonal NdPtSb-type structure (space group P63mc).
Magnetization measurements performed for field configuration H||c and H||ab
show that GdAuGe orders antiferromagnetically at the Neel temperature, TN =
17.2 K. Around this temperature, heat capacity and electrical resistivity data
exhibit prominent anomaly due to the antiferromagnetic (AFM) transition. In
addition to an AFM phase transition, the magnetization data for H||c display
the signature of field-induced metamagnetic (MM) transitions below TN. The
critical field range for these transitions vary from 0.2 to 6.2 T. The critical
fields for the MM transitions decrease with increasing temperature and approach
zero value for temperature approaching TN. Interestingly, the magnetoresistance
(MR) data (for H||c) record a sharp increase in values at the critical fields
that coincide with those seen in magnetization data, tracking the presence of
MM transitions. MR is positive and large (169% at 9 T and 2 K) at low
temperatures. Above TN, MR becomes small and switches to negative values. Hall
resistivity data reveal the predominance of hole charge carriers in the system.
In addition, we observe an emergence of step-like feature in the Hall
resistivity data within the field range of second MM, and a significantly large
anomalous Hall conductivity of 1270 {\Omega}-1 cm-1 at 2 K. The H-T phase
diagram constructed from our detailed magnetization and magnetotransport
measurements reveals multiple intricate magnetic phase transitions. The
electronic and magnetic structure of GdAuGe are also thoroughly investigated
using first-principles methods. The electronic band structure calculations
reveal that GdAuGe is a Dirac nodal-line semimetal.
