No abstract

Evidence of multiband behavior in the superconducting alloy Zr 0.96V0.04B2 ZrB 2 is a nonsuperconducting Pauli paramagnetic crystallizing in the AlB 2 structure. V substitution for Zr in Zr 1−x V x B 2 (0.01 x 0.1) at the few percentage level induces superconductivity with critical temperature reaching a maximum of 8.7 K for Zr 0.96 V 0.04 B 2 near the solid solubility limit. Specific-heat and lower critical field temperature dependence results suggest the possibility of unconventional superconductivity possibly arising from multiband effects.

Superconducting bulk properties of ternary Nb2BN are confirmed and are described by means of magnetization, electronic transport and specific-heat measurements. BCS conventional superconductivity is found with Tc = 4.4 K. Critical fields Hc1(0)= 93 Oe and Hc2(0)= 2082 Oe are extrapolated by magnetic and resistivity measurements. The specific heat data reveals γ = 6.3 mJ/mol K 2 and β = 0.293 mJ/mol K 4 in good agreement with the BCS Theory.

We have investigated the critical current density (Jc) and the flux pinning behavior in Zr0.96V0.04B2 superconductor with an AlB2 structure. V substitutions in Zr sites of non-superconducting ZrB2 system lead to superconductivity, and the 4% V-substituted Zr0.96V0.04B2 compounds show the highest superconducting transition temperature (Tc) of ∼8.7 K. The magnetic hysteresis (M−H) loops for the Zr0.96V0.04B2 demonstrate type-II superconducting behavior in a broad temperature range, and the Jc is estimated from the M−H loops using the Bean model. The analysis of the double-logarithmic Jc(H) plots indicates the dominance of collective pinning in Zr0.96V0.04B2, and that Jc(H) and magnetic field dependences of the flux pinning force density (Fp) are well fitted by the double exponential model which takes into account the existence of two superconducting gaps.

In this work, we report superconductivity at 5.5 K in the new pseudo-ternary Th 0.93 Zr 0.07 B 12 compound. We show clearly evidence that appropriate amounts of Zr substitution at the Th site induce the stabilization of the UB 12 prototype structure at ambient pressure. The superconducting bulk properties of Th 0.93 Zr 0.07 B 12 are confirmed by means of magnetization, electronic transport properties and specific heat measurements. The H-T phase diagrams based on magnetization and magnetoresistance measurements yield μ 0 H c1 (0) = 6 mT and μ 0 H c2 (0) = 98 mT and allow us to estimate the coherence length ξ o ∼ 57.9 nm and the penetration depth λ L ∼ 234 nm at zero kelvin.