AnomalouslyWeak Cooper Pair-breaking by Exchange Energy in Ferromagnet/Superconductor Bilayers

作者：Lemberger T R; Hinton M J^*; Yong Jie; Lucy J M; Hauser A J; Yang F Y

来源：Journal of Superconductivity and Novel Magnetism, 2014, 27(10): 2249-2255.

DOI：10.1007/s10948-014-2591-3

• Proximity effect
• Ferromagnetism
• Thin films
• Multilayers
• Interfaces

We report the superconducting transition temperature T-c versus thickness d(F) of Ferromagnet/Superconductor (F/S) bilayers, where F is a strong 3d ferromagnet (Ni, Ni-0.81 Fe-0.19 (Permalloy), Co0.5Fe0.5) and S = Nb, taken from superfluid density measurements rather than resistivity. By regrouping the many physical parameters that appear in theory, we show that the effective exchange energy is determined from the F film thickness d(F) where T-c versus d(F) begins to flatten out. Using this rearranged theory, we conclude 1) the effective exchange energy, E-ex, is about 15 times smaller than measured by ARPES and five times smaller than deduced in previous studies similar to ours; 2) the dirty-limit coherence length, xi(F), for Cooper pairs in F is larger than the electron mean free path, l(F); and 3) the 3d-F/Nb interface is enough of a barrier that Cooper pairs typically must hit it several times before getting through. The Py/Nb and CoFe/Nb interfaces are more transparent than the Ni/Nb interface.

• 出版日期2014-10