  Polycrystalline samples of the recently discovered MgCNi3 superconductor were
investigated by transport, ac susceptibility, dc magnetization and specific
heat measurements in magnetic fields up to 16 T. Consistent results were
obtained for the temperature dependence of the upper critical field H_c2(T)
from resistance, ac susceptibility and specific heat measurements. A WHH like
temperature dependence of H_c2(T) and the quadratic relationship H_c2(0) ~
T_c^2 point to an effective predominant single band behavior near the quasi
clean limit. Evidence for strong electron-phonon and electron-paramagnon
coupling was found analyzing the specific heat data. The corresponding s- and
p-wave scenarios are briefly discussed using calculated densities of states of
different Fermi surface sheets.
