Comparison of superconducting parameters of A 15- and σ-phases of Nb−Pt
The superconducting properties of A 15- and σ-phases of the system Nb−Pt were investigated. Alloys of compositions Nb3Pt, Nb2Pt, and Nb62Pt38 were prepared by arc melting and subjected to optical microscopic and x-ray analysis for structure determination. The transition temperatures were measured inductively as well as resistively. The temperature dependences of critical fields were measured up to 35 kG. The A 15-phase has aT c value of 8.97K and a zero temperature upper critical fieldH c2(0) of 100 kG as compared to aT c value of 2.14K and anH c2(0) value of 14kG for the σ-phase. A comparison with theoretical upper critical field values seems to indicate that a spin-orbit coupling mechanism is responsible for the higher value ofH c2(0) in the case of the A 15-phase alloy. The temperature dependent resistance up to 300 K is also measured and discussed for both the phases.
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