Zero-Field Cooled Specific Heat Of FeCl3 Intercalated Graphite

Specific heat measurements have been carried out down to below 0.5 K on a stage 5 sample that was cooled in zero magnetic field using a mu-metal shield. In these measurements the specific heat anomaly is lowered to the temperature T ~ 0.8 K. Furthermore, the removal of the magnetic shield does not restore the higher temperature anomaly, even after the sample's temperature was raised above 10 K. The data also show a T2 behavior above 1.4 K for the lattice component (D ~ 160 K), which is indicative of a 2D phonon spectrum. However, similar measurements on a stage 2 sample just reproduced the phase transition at ~ 1.8 K, while extending the temperature range allowing measurements of the electronic contribution to the specific heat.