Superconducting properties of amorphous Zr-Ge binary alloys

Abstract

A new type of refractory metal-metalloid amorphous alloys exhibiting superconductivity has been found in a binary Zr-Ge system by a modified melt-spinning technique. Specimens are in the form of continuous ribbons 1 to 2 mm wide and 0.02 to 0.03 mm thick. The germanium content in the amorphous alloys is limited to the range of 13 to 21 at%. These amorphous alloys are so ductile that no cracks are observed even after closely contacted bending test. The Vickers hardness and crystallization temperature increase from 435 to 530 DPN and from 628 to 707 K, respectively, with germanium content, and the tensile fracture strength is about 1460 MPa. Furthermore, the amorphous alloys exhibit a superconducting transition which occurs very sharply. The superconducting transition temperature (Tc) increases with decreasing germanium content and reaches a maximum value of 2.88 K for Zr87Ge13. The upper critical magnetic field for Zr87Ge13 alloy was of the order of 21.8 kOe at 2.0 K and the critical current density for Zr85Ge15 alloy was about 175 A cm−2 at 1.70 K in the absence of an applied field. The upper critical field gradient atTc and the electrical resistivity at 4.2 K increase significantly from 24.6 to 31.5 kOe K−1 and from 235 to 310μΩcm, respectively, with the amount of germanium. The Ginzburg-Landau (GL) parameterк and the GL coherence length §GL (0) were estimated to be 72 to 111 and about 7.9 nm, respectively, from these experimental values by using the Ginzburg-Landau-Abrikosov-Gorkov (GLAG) theory and hence it is concluded that the Zr-Ge amorphous alloys are extremely “soft” type-II superconductor with high degree of dirtiness which possesses theTc values higher than zirconium metal, in addition to high strength combined with good ductility.