  In epitaxial (111) oriented Ni$_{80}$Fe$_{20}$/Fe$_{50}$Mn$_{50}$ bilayers,
we separate two distinct behaviors: unidirectional anisotropy (exchange bias)
in thick Fe$_{50}$Mn$_{50}$, and enhanced coercivity in thin
Fe$_{50}$Mn$_{50}$. By measuring the magnetization response to a rotating
magnetic field, we quantitatively determine the relevant anisotropies, and
demonstrate that the enhanced coercivity is related to the rotatable magnetic
anisotropy of Fe$_{50}$Mn$_{50}$. We also demonstrate the consequences of the
anisotropy changes with temperature.
