  Ferromagnetic films with perpendicular magnetic anisotropy are of interest in
spintronics and superconducting spintronics. Perpendicular magnetic anisotropy
can be achieved in thin ferromagnetic multilayer structures, when the
anisotropy is driven by carefully engineered interfaces. Devices with multiple
interfaces are disadvantageous for our application in superconducting
spintronics, where the current perpendicular to plane is affected by the
interfaces. Robust intrinsic PMA can be achieved in certain Co$_x$Pt$_{100-x}$
alloys and compounds at any thickness, without increasing the number of
interfaces. Here, we grow equiatomic Co$_{50}$Pt$_{50}$ and report a
comprehensive study on the structural, magnetic, and spin-polarisation
properties in the $L1_1$ and $L1_0$ ordered compounds. Primarily, interest in
Co$_{50}$Pt$_{50}$ has been in the $L1_0$ crystal structure, where layers of Pt
and Co are stacked alternately in the [100] direction. There has been less work
on $L1_1$ crystal structure, where the stacking is in the [111] direction. For
the latter $L1_1$ crystal structure, we find magnetic anisotropy perpendicular
to the film plane. For the former $L1_0$ crystal structure, the magnetic
anisotropy is perpendicular to the [100] plane, which is neither in-plane or
out-of-plane in our samples. We obtain a value for the ballistic spin
polarisation of the $L1_1$ and $L1_0$ Co$_{50}$Pt$_{50}$ to be $47\pm3\%$.
