PROXIMITY EFFECT IN SUPERCONDUCTOR FERROMAGNET LAYERED SYSTEM - INFLUENCE OF SUPERCONDUCTIVITY ON MAGNETIC-PROPERTIES OF NB/FE EPITAXIAL BILAYERS/

Magnetic and superconducting properties of Fe/Nb epitaxial bilayers ha ve been studied. Single crystal Fe/Nb (110) bilayers with a Nb thickne ss d(Nb) in the range from 250 to 650 Angstrom and with a Fe thickness d(Fe) in the range from 7 to 27 Angstrom were prepared using molecula r beam epitaxy techniques. Magnetization measurements showed the exist ence of a magnetically ''dead'' Fe-interface layer with a thickness d( NM) varying strongly with minor modifications of the growth conditions . For bilayers with a small magnetic layer thickness d(M) and a small d(NM) the FMR measurements revealed an anomalous decrease of the effec tive magnetization 4 pi M-eff of the ferromagnetic Fe layer below the superconducting transition temperature T-c. The absolute change of 4 p i M-eff below T-c depends strongly on the actual values of d(M) and d( NM): upon decreasing both d(M) and d(NM) the effect increases consider ably. As a possible mechanism for the anomalous temperature dependence of 4 pi M-eff below T-c we discuss a spatial modulation of ferromagne tic order due to a modification of the RKKY interaction in the superco nducting state.