  Different layer thicknesses of Cobalt ranging from 2.6 {\AA} (1.5 ML) up to
55 {\AA} (30.5 ML) deposited on ferroelectric BaTiO$_3$ have been studied
regarding their magnetic behavior. The layers have been characterized using
XMCD spectroscopy at remanent magnetization. After careful data analysis the
magnetic moments of the Cobalt could be determined using the sum rule
formalism. There is a sudden and abrupt onset in magnetism starting at
thicknesses of 9 {\AA} (5 ML) of Cobalt for measurements at 120 K and of 10
{\AA} (5.5 ML) if measured at room temperature. Initial island growth and
subsequent coalescence of Co on BaTiO$_3$ is suggested to explain the sudden
onset. In that context, no magnetically dead layers are observed.
