  Magnetotransport is investigated in thin films of the half-metallic
ferrimagnet Mn$_2$Ru$_x$Ga in pulsed magnetic fields of up to 58 T. A
non-vanishing Hall signal is observed over a broad temperature range, spanning
the compensation temperature 155 K, where the net magnetic moment is strictly
zero, the anomalous Hall conductivity is 6673 $\Omega^{-1}.m^{-1}$ and the
coercivity exceeds 9 T. Molecular field modelling is used to determine the
intra- and inter-sublattice exchange constants and from the spin-flop
transition we infer the anisotropy of the electrically active sublattice to be
216 kJ/m$^3$ and predict the magnetic resonances frequencies. Exchange and
anisotropy are comparable and hard-axis applied magnetic fields result in a
tilting of the magnetic moments from their collinear ground state. Our analysis
is applicable to collinear ferrimagnetic half-metal systems.
