AC Microcalorimetry of Superconducting MgCNi_3 Single Crystals

The low-temperature speci¯c heat of single-crystal samples of super- conducting MgCNi3 with typical dimensions 200 ¹m were measured for the ¯rst time. A computer controlled ac microcalorimeter using an optical ¯ber and an infrared light-emitting diode as the heat source was used down to 2 K at magnetic ¯elds up to 8 T. The speci¯c heat data suggest a moderate coupling in MgCNi3.