Effect of ferromagnetic film thickness on magnetoresistance of thin-film superconductor-ferromagnet hybrids

We study the influence of the thickness D(f) of the plain ferromagnetic (F) film on the electrical resistance of the flux-coupled hybrids, consisting of superconducting (S) Al film and multilayer [Co/Pt] F film with out-of-plain magnetization. The behavior of such hybrids at high and low temperatures is found to be different as follows: the nucleation of superconductivity at high temperatures is governed mainly by the typical lateral dimensions of the magnetic domains, while low-temperature properties are determined by topology of the magnetic template. We show that an increase in the D(f) value leads to a broadening of the field-intervals and temperature intervals where nonmonotonous dependence of the superconducting critical temperature T(c) on the applied magnetic field H is observed (for demagnetized F films). Further increase in the Df value results in a global suppression of superconductivity. Thus, we determined an optimal thickness, when the nonmonotonous dependence T(c)(H) can be observed in rather broad T and H range, what can be interesting for further studies of the localized superconductivity in planar Al-based S/F hybrids and for development of the devices which can exploit the localized superconductivity. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3457844]