Upper Critical Field and Hall effect in superconducting perovskite $MgCNi_3$

Upper critical field $H_{c2}$ and Hall coefficient $R_H$ in superconducting perovskite $MgCNi_3$ have been studied. The normal state $\rho(T)$ behavior is similar to that observed in oxide perovskite $(Ba,K)BiO_3$ (BKBO), in which $\rho(T)$ fits well curve predicted by Bloch-Gr\"{u}neisen theory consistently with electron-phonon scattering. $H_{c2}(T)$, determined from the onset of the resistive superconducting transition under magnetic fields, can be described by an expression $H_{c2}(T)$ = $H_{c2}(0)[1-(T/T_c)^2]$ with the zero-temperature critical field $H_{c2}(0)$ = 8.1 T followed by conventional type-II superconductors. It is found that $R_H$ of $MgCNi_3$ is negative and its magnitude increases as temperature decreases. At T = 100 K, $R_H$ = $-4.3 \times 10^{-10} m^3/C$, and the calculated carrier density is $1.4 \times 10^{22}/cm^3$, which is comparable with that in perovskite $(Ba,K)BiO_3$, and less than that of the metallic binary $MgB_2$.