Specific heat of aligned multiwalled carbon nanotubes

The specific heat of an aligned bulk multiwalled carbon nanotube sample made by the chemical vapour deposition method was measured from 250 to 1.8 K. The specific heat curve gradually decreased, showing one-dimensional (1D) behaviour down to 40 K. Below 40 K it showed a rapid decrease due to the dimensional change from 1D to 3D behaviour, indicated by different temperature dependences at low temperature. Interestingly, a T−2 term was observed below 5 K, suggesting a nuclear hyperfine component due to magnetic impurities which were confirmed to be present by thermogravimetric analysis and microscopy observations.