Spin fluctuations in metallic glasses Zr75(NixFe1-x)25 at ambient and higher pressures

The superconducting properties of metallic glasses Zr75(NixFe1-x)25 (x=0,0.25,0.50,0.75,1.0) were studied both at ambient pressure and under quasihydrostatic pressure up to 8 GPa (80 kbar). To obtain information on the spin fluctuation parameter SF the following measurements were carried out: the dc magnetic susceptibility, the upper critical field at the ambient pressure superconducting transition temperature Tc (P=1 bar), mass density, and room temperature resistivity. From the pressure dependence of the superconducting transition temperature Tc(P) in Cu25Zr75 glass, we estimate the volume derivative of the electron-phonon (e-ph) coupling parameter e-ph in this alloy using the McMillan equation. This is used as a reference value for the volume derivative of e-ph in the Zr75 (NixFe1-x)25 alloys. Using the modified McMillan equation, which includes spin fluctuation effects and the above reference value for the volume derivative of the e-ph coupling parameter, we determine e-ph, the electron-spin fluctuation coupling parameter SF, and the rate of suppression of spin fluctuations with the pressure (d lnSF/d lnV) as a function of Fe concentration in these alloys. Both spin fluctuations and the rate of suppression of spin fluctuations with pressure (d lnSF/d lnV) are found to increase with higher Fe concentration in these alloys.