Superconducting properties of MgCNi₃ films

We report the magnetotransport properties of thin polycrystalline films of the recently discovered nonoxide perovskite superconductor MgCNi₃. CNi₃ precursor films were deposited onto sapphire substrates and subsequently exposed to Mg vapor at 700°C. We report transition temperatures (T_c) and critical field values (H_c2) of MgCNi₃ films ranging in thickness from 7.5 nm to 100 nm. Films thicker than ≈40 nm have a T_c∼8 K, and an upper critical field H_c2(T=0)=14T, which are both comparable to that of polycrystalline powders. Hall measurements in the normal state give a carrier density, n=-4.2×10²²cm^-3, that is approximately 4 times that reported for bulk samples.