Phase instability, spin fluctuations, and superconductivity in the C15 compound V2Zr

From low-temperature measurements of the specific heat and the magnetic susceptibility, we determined T/sub c/, γ, and chi/sup spin/ for both the cubic and the rhombohedral phase of the C15 compound V2Zr. In addition, neutron-diffraction experiments were performed for a proper identification of these two phases. We found that the martensitic transformation (T/sub M/approx.110 K) from the cubic to the rhombohedral phase leads to a substantial reduction in γ and chi/sup s/pin: γcub (γ/sub r/h)approx.23 (16) mJ/g-at.K2 and chi/sub c/ub/sup s/pin (chi/sub rh//sup spin/)approx.2.1 x 10-7 (1.4 x 10-4) emu/g-at. In contrast, T/sub c/ is only slightly changed: T/sub c//sup cub/approx.8.7 K and T/sub c//sup rh/approx.8.0 K. Together with the fact that the ''Wilson ratio'' N(chi)/N(γ)approx.0.7 in both phases, we take our findings as clear evidence that in V2Zr T/sub c/ is limited by spin fluctuations