Superconducting behaviour of Nb-Fe multilayers

Superconductor-ferromagnetic multilayer structures offer an opportunity to investigate the superconducting behaviour in the presence of interesting ef fects such as inelastic electron scattering from virtual bound states, magn etic spin flip scattering and the magnetic exchange potential etc. Wong et al. [J. Low Temp. Phys. 63 (1986) 307] first reported a non-monotonic varia tion of T-c as a function of layer thickness of magnetic material in V-Fe m ultilayers. Subsequently, similar behaviour has also been reported in such multilayers by several groups. While non-monotonic variation of T-c has bee n interpreted by a few groups as arising from the stabilisation of the pi p hase in specific thickness regimes, this is highly controversial. In view o f the current interest in the superconducting behaviour of such structures, we have carried out studies on superconducting behaviour of Nb-Fe multilay ers deposited by the RF magnetron sputtering-technique. Multilayers were ph otolithographic ally patterned into a geometry suitable for current-in-plan e (CIP) measurements. Each multilayer consisted of seven layers of Nb and s even layers of Fe. In different multilayers, layer thickness of Nb (dx) was held constant at 450 Angstrom, while the thickness of the magnetic Fe laye r (d(Fe)) was progressively varied from 4.5 to 18 Angstrom. Another set of Nb-Fe multilayers was also prepared by changing the Nb layer thickness to 2 00 Angstrom. In the multilayers with d(Nb) = 450 Angstrom, our preliminary results show a non-monotonic variation of T-c with d(Fe). (C) 2001 Elsevier Science BY All rights reserved.