COUPLING PHENOMENA IN SUPERCONDUCTING NB FE MULTILAYERS/

We measured the critical temperature T-c and critical field H-c2 of mo lecular-beam epitaxy-grown Nb/Fe multilayers in which the layer thickn esses t(Fe) and t(Nb) are systematically varied. For constant t(Nb) we observe a continuous decrease of T-c with increasing t(Fe) up to t(Fe )= 15 Angstrom. At higher t(Fe) values a sudden drop of T-c is measure d related to the onset of ferromagnetism in the Fe layers. Measurement s of the shape and the angular dependence of H-c2(T) clearly show that the superconducting Nb layers are already decoupled for t(Fe) = 12 An gstrom, magnetization measurements, however show that the Fe layers ar e ferromagnetic only for t(Fe) greater than or equal to 16 Angstrom. F or constant t(Fe)= 25 Angstrom, the observed strong decrease of T-c wi th decreasing Nb thickness as well as the temperature dependence of H- c2 are well described by the theoretical model for decoupled supercond uctor/ferromagnet multilayers.