  The effect of interface roughness of ferromagnetic and antiferromagnetic
layers on exchange bias is still not well understood. In this report we have
investigated the effect of surface roughness in (111)-oriented
antiferromagnetic CoO films on exchange bias with ferromagnetic Fe grown on
top. The surface roughness is controlled at the atomic scale, over a range
below ~ 0.35 nm, by varying layer thickness of the CoO films. It is observed
that both exchange bias field ($H_{E}$) and coercivity ($H_{C}$) extensively
depend on the atomic scale roughness of the CoO (111) at the interface with Fe
film. An opposite dependence of $H_{E}$ and $H_{C}$ on interface roughness was
found, which was ascribed to partially compensated spin states induced by the
atomic roughness at the fully uncompensated CoO (111) surfaces and was
corroborated using the Monte Carlo simulations. Moreover, the onset temperature
for $H_{C}$ is found to be up to ~ 80 K below the blocking temperature
($T_{B}$) and the temperature dependence of $H_{C}$ follows the power law with
a critical exponent equal to one, which indicates that, in this system, $H_{C}$
is more of an interface-related property than $H_{E}$.
