Correlation of Superfluid Density and $T_c $ Suppression in Superconducting/Ferromagnetic Bilayers

We report superfluid density measurements of thin film Nb and ferromagnet (Ni, Py, CoFe) bilayers. Data were taken by mutual inductance measurement using a two-coil technique on samples prepared with UHV sputtering. We present data showing, as the thickness of the ferromagnet increases, $T_c $ and superfluid density are suppressed to a limiting value. The limiting value in $T_c $ and superfluid density depends on the exchange field of the ferromagnet as well as the transparency of the interface. Values for $T_c $ and superfluid density at $T=0\mbox{ K}$ follow reasonably well the theory for bilayers with superconducting layer less than a coherence length thick despite our samples consisting of a superconducting layers more than twice a coherence length.