  Two-dimensional (2D) van der Waals (vdWs) materials have gathered a lot of
attention recently. However, the majority of these materials have Curie
temperatures that are well below room temperature, making it challenging to
incorporate them into device applications. In this work, we synthesized a
room-temperature 2D magnetic crystal Fe$_5$GeTe$_2$ with a Curie temperature
$T_c$ = 332 K, and studied its magnetic properties by vibrating sample
magnetometry (VSM) and broadband ferromagnetic resonance (FMR) spectroscopy.
The experiments were performed with external magnetic fields applied along the
$c$-axis ($H\parallel c$) and the $ab$-plane ($H\parallel ab$), with
temperatures ranging from 300 K to 10 K. We have found a sizable Land\'e
$g$-factor difference between the $H\parallel c$ and $H\parallel ab$ cases. In
both cases, the Land\'e $g$-factor values deviated from $g$ = 2. This indicates
a possible contribution of orbital angular momentum to the magnetic moment but
may also be caused by lack of saturation at FMR. The FMR measurements also show
a broadened linewidth at low temperatures; together with the VSM data, our
measurements indicate that magnetic domains of different orientations develop
within Fe$_5$GeTe$_2$ in both $H\parallel ab$ and $H\parallel c$ cases, with a
higher level of randomness in the $H\parallel c$ case, especially at lower
temperatures. Our experiments highlight key information regarding the magnetic
state and spin scattering processes in Fe$_5$GeTe$_2$, which promote the
understanding of magnetism in Fe$_5$GeTe$_2$, leading to implementations of
Fe$_5$GeTe$_2$ based room-temperature spintronic devices.
