Specific heat and magnetic susceptibility of nearly stoichiometric and homogeneousNb3Al

Abstract

$A$ 15-type ${\mathrm{Nb}}_3$Al has been characterized in the recent past as a "high-$T_c$, low-$\gamma$ superconductor," where $\gamma$ is the electronic specific-heat coefficient. We show that this statement should be revised, previous analyses simply reflecting the imperfect metallurgical state. We succeeded in preparing homogeneous, nearly stoichiometric, bulk ${\mathrm{Nb}}_3$Al and reinvestigated the specific heat (from 1 to 50 K) and the magnetic susceptibility (19-300 K) in the highly ordered and a slightly disordered condition. The new results show that ordered ${\mathrm{Nb}}_3$Al exhibits a high electronic density of states ($\gamma =11.4\mathrm{}$ mJ ${\mathrm{K}}^{-2\mathrm{}}$ ${\mathrm{g}-\mathrm{a}\mathrm{t}.\mathrm{}}^{-1\mathrm{}}$, $N\left(0\right)\mathrm{}\cong 0.91$ e${\mathrm{V}}^{-1\mathrm{}}$ ${\mathrm{atom}}^{-1\mathrm{}}$ ${\mathrm{spin}}^{-1\mathrm{}}$). Information is provided on the moments of the phonon spectrum and those of the electron-phonon spectral function, the thermodynamical critical field, and the energy gap 2▵(0). The present experiments further establish only weak exchange enhancement of the susceptibility; spin fluctuations may therefore be safely neglected. Specific-heat data are also reported for the neighboring $\sigma$-phase ${\mathrm{Nb}}_2$Al.