Abstract Body

Superconductivity in Zr₆FeSb₂ was investigated through low-temperature specific heat measurements. Polycrystalline samples were synthesized by arc-melting, followed by annealing. Powder X-ray diffraction (PXRD) and electron-probe microanalysis (EPMA) revealed that the obtained samples were phase-pure Zr₆FeSb₂ with secondary phases comprising less than 2%. Superconductivity was observed below 1.3 K, as evidenced by electrical resistivity and AC magnetic susceptibility measurements [1]. Figure 1 shows the electronic specific heat divided by temperature C_e/T as a function of temperature T, measured at magnetic fields of 0 T and 0.6 T. In the superconducting state at 0 T, we observed a broad superconducting transition, indicated by a peak at 0.75 K, and a large residual electronic specific heat coefficient γ_res = 39 mJ/K²mol. This value is approximately 57% of the normal-state electronic specific heat coefficient γ_N = 68 mJ/K²mol, as determined from the 0.6 T data. The large γ_res does not originate from secondary phases, as PXRD and EPMA showed that the sample was nearly single-phase. We suggest that significant pair-breaking occurs due to paramagnetic impurities, as indicated by the low-temperature Curie tail observed in the magnetic susceptibility in the normal state. This system can exhibit mixing between Fe and Sb, expressed as Zr₆Fe_1-xSb_2+x (0.0 ≤ x ≤ 0.3) [2]. Fe ions in the Sb site may possess paramagnetic moments, resulting in magnetic pair-breaking in the superconducting state. Further study is warranted.

References

[1] R. Matsumoto et al., J. Phys. Soc. Jpn. 93, 065001 (2024).

[2] G. Melnyk et al., J. Phase Equilibria 20, 497 (1999).

Figure 1. Electronic specific heat divided by temperature, C_e/T, as a function of temperature T. Closed and open circles represent data measured under magnetic fields of 0 T and 0.6 T, respectively. The solid curve shows the calculated C_e/ in the BCS weak coupling limit with a thermodynamic critical temperature of. T_c = 0.95 K and a residual electronic specific heat coefficient γ_res of 39 mJ/K²mol. The dashed curve represents the calculated Ce/T assuming Gaussian broadening of T_c with a standard deviation of 0.15 K

Keywords:Specific heat, Zr₆FeSb₂, Metal rich compound