Critical current density and flux pinning in Zr0.96V0.04B2 superconductor with AlB2 structure

Soon-Gil Jung,S T Renosto,V V Moshchalkov,C A M Dos Santos,Z Fisk,J Albino Aguiar,J Vanacken,A J S Machado

doi:10.1063/1.4821283

Abstract

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.

Highlights

We have investigated the critical current density (Jc) and the flux pinning behavior in Zr0.96V0.04B2 superconductor with an AlB2 structure
Reduced field dependences of the normalized flux pinning force density (fp) are well scaled by the double exponential model in comparison with a generally used model for flux pinning force scaling, such as Kramer model

Summary

Introduction

The discovery of the superconducting transition at $40 K in MgB2 has brought about great interest to materials with an AlB2 structure (space group P6/mmm) because of their potential for having a high superconducting transition temperature (Tc). AlB2-type metal diborides, such as NbB2, ZrB2, TaB2, and so on, have been extensively studied, and a superconducting transition is observed in nonstoichiometric boride compounds such as MoB2þx and NbB2þx. In addition, AgB2 and AuB2 were predicted to have Tc higher than 50 K from the theoretical estimates, but recently much lower Tc $ 7 K than theoretically predicted was found experimentally in AgB2 thin films. It should be noted that, despite a favorable prediction of their high Tc, it is difficult to synthesize these materials with an AlB2 structure.ZrB12 shows a superconductivity below $6 K and has an UB12 structure.22Very recently, we have studied the effect of the V substitution for the Zr site in ZrB2 compounds and found its favorable effect on Tc. The discovery of the superconducting transition at $40 K in MgB2 has brought about great interest to materials with an AlB2 structure (space group P6/mmm) because of their potential for having a high superconducting transition temperature (Tc).. AlB2-type metal diborides, such as NbB2, ZrB2, TaB2, and so on, have been extensively studied, and a superconducting transition is observed in nonstoichiometric boride compounds such as MoB2þx and NbB2þx.. Basic properties of these compounds suggest a multiband behavior, and they have a high upper critical field (Hc2(0)) of $16 T in spite of a low Tc, which make these material more interesting for further studies. The study on the Jc and flux pinning force for metal diboride superconductor with multigap except for MgB2 is rarely reported, they are very important factors for basic properties and real applications in superconductor

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