  The quasi-two-dimensional van der Waals magnet Fe$_{5-\delta}$GeTe$_2$ has
emerged as a promising platform for electronic and spintronic functionalities
at room temperature, owing to its large ferromagnetic ordering temperature
$T_{\text{C}}$ $\sim$ 315 K. Interestingly, by cobalt (Co) substitution of iron
in F5GT, $i.e.$ $({\text{Fe}}_{1-x}{\text{Co}}_x)_{5-\delta}{\text{GeTe}}_2$
(Co-F5GT), not only can its magnetic transition temperature be further
enhanced, but the magnetic and structural ground states can also be tuned.
Specifically, an antiferromagnetic (AFM) order is induced beyond the Co doping
level $x \ge 0.4$. Here, we investigate the magnetic properties of a Co-F5GT
single crystal at $x = 0.45(1)$, by utilizing the element specific, resonant
magnetic x-ray scattering technique. Our study reveals an A-type, Ising-like
AFM ground state, with a transition temperature $T_{\text{N}}$ $\sim$ 340 K. In
addition, our work unveils an important contribution from Co magnetic moments
to the magnetic order. The application of the in-plane magnetic fields
gradually polarize the spin moments along the field direction, but without
inducing incommensurate spin texture(s).
