Effect of magnetic iron impurity on the superconducting properties of an amorphous Nb50Zr35Si15 alloy

Abstract

The effect of magnetic iron impurity on the superconducting properties of amorphous Nb50Zr35−x Si15Fe x (x⩽4 at %) alloys was examined. Doping with an iron impurity resulted in a linear depression ofT c andH c2(T) and a decrease in $$(dH_{c2} /dT)_{T_c } $$ andρ n after reaching a maximum value at 0.5 to 1.0 at % iron. The observed decrease was about 35% forT c, 85% forH c2 at 2.0 K, 16% for $$(dH_{c2} /dT)_{T_c } $$ and 21% forρ n. Although the decrease in $$(dH_{c2} /dT)_{T_c } $$ occurs through the decrease inρ n as expected from the GLAG theory, the depression inT c caused by magnetic impurity could not be explained in terms of the GLAG theory which is applicable to Nb-Zr-Si amorphous alloys without magnetic impurity, but was interpreted as arising from the pair-breaking effect in the superconducting nature due to magnetic scattering. However, the pair-breaking effect was found to be smaller by about one-tenth for the present amorphous superconductors than for crystalline superconductors, indicating the high stability of the superconductivity of the Nb-Zr-Si-Fe alloys against the magnetic scattering arising from the magnetic impurity. The reduced magnetic field at which the reduced fluxoid pinning force exhibits a maximum value increased with iron concentration, indicative of an enhancement of fluxoid pinning force. The enhancement in fluxoid pinning force was interpreted as arising from the increase in compositional, electronic and/or magnetic fluctuations by the dope of iron impurity.