Superconductivity in layered Nb/Gd films

Abstract

The transition temperature and the critical fields of electron-beam evaporated Nb/Gd/Nb triple layers and Nb/Gd multilayers have been determined by measurements of the electrical resistivity and the dc susceptibility. For constant thickness dGd of the Gd layers, we observe a decrease of Tc and Hc2⊥ with decreasing thickness dNb of Nb layers down to a critical thickness dc, below which superconductivity is completely destroyed. The parallel critical fields mostly show the square-root temperature dependence near Tc, typical for two-dimensional superconductors. As predicted theoretically, competing pair-breaking mechanisms lead to a nonmonotonic dependence of Hc∥ on dNb. We have also studied the dependence Tc(dGd) with constant dNb and find a decrease of the Tc(dGd) curve with increasing dGd and a steplike structure at dGd≊20 Å. To clarify the nature of this step, the ferromagnetic transition of the Gd films is determined with the transverse magneto-optical Kerr effect. Long-range magnetic order is found only above dGd≊20 Å, which is attributed to the formation of a discontinuous film below this thickness. These results indicate a change in the underlying pair-breaking mechanism.

Source-reported materials — not catalogue approval

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