  Geometrical frustration and the enhancement of strong quantum fluctuations in
two-dimensional triangular antiferromagnets can lead to various intriguing
phenomena. Here, we studied the spin-1/2 triangular lattice antiferromagnet
NdAuAl$_4$Ge$_2$. Thermodynamic and transport properties, such as magnetization
and specific heat together with the resistivity measurements were performed. In
zero field, two successive phase transitions were observed at $T_{\rm
N1}=1.75\pm 0.02$ K and $T_{\rm N2}=0.49\pm 0.02$ K, respectively. Under
magnetic field, $\rm XXZ$-type anisotropy was revealed, with the moments
pointing along the easy $c$ axis. For $B\parallel c$, multiple field-induced
states were observed, and the magnetic phase diagram was established based on
the specific heat and magnetization data. The temperature-dependent resistivity
measurements indicate that NdAuAl$_4$Ge$_2$ is a good metal. It is very likely
that both the long-range RKKY interactions and the geometrical frustration play
an important roles in this case.
