  We present calculations and experimental measurements of the
temperature-dependent magnetization of a single crystal of GdCo$_5$ in magnetic
fields of order 60 T. At zero temperature the calculations, based on
density-functional theory in the disordered-local-moment picture, predict a
field-induced transition from an antiferromagnetic to a canted alignment of Gd
and Co moments at 46.1 T. At higher temperatures the calculations find this
critical field to increase along with the zero-field magnetization. The
experimental measurements observe this transition to occur between 44-48 T at
1.4 K. Up to temperatures of at least 100 K, the experiments continue to
observe the transition; however, at variance with the calculations, no strong
temperature dependence of the critical field is apparent. We assign this
difference to the inaccurate description of the zero-field magnetization of the
calculations at low temperatures, due to the use of classical statistical
mechanics. Correcting for this effect, we recover a consistent description of
the high-field magnetization of GdCo$_5$ from theory and experiment.
