  We have measured resonant soft x-ray diffuse magnetic scattering as a
function of temperature in a positively exchange biased Co/FeF2 bilayer and
analyzed the data in the distorted wave Born approximation to obtain in-plane
charge and magnetic correlation lengths associated with the Co and FeF2 layers
and estimate interfacial roughness. Tuning to the Fe and Co L3 edges reveals
significantly different temperature trends in these quantities in the
antiferromagnetic and ferromagnetic layers, respectively. While the magnetic
correlation length of the uncompensated interfacial spins in FeF2 layer
increase as temperature decreases, these quantities remain unchanged in the Co
layer. Our results indicate that uncompensated Fe spins order within a range of
few hundred nanometers in otherwise randomly distributed uncompensated magnetic
moments, giving rise to spin clusters in the antiferromagnet whose size
increase as the temperature decrease.
