  We report magnetic measurements up to 1100 K on a multi-walled carbon
nanotube mat sample using a Quantum Design vibrating sample magnetometer. In an
ultra-low field (H = -0.02 Oe), we find a very large paramagnetic
susceptibility (up to 12.7% of 1/4pi) at 1100 K and a very large diamagnetic
susceptibility (at least 8.4% of -1/4pi) at 482 K. A small magnetic field (2.1
Oe) completely suppresses the diamagnetic susceptibility at 482 K and reduces
the paramagnetic susceptibility at 1100 K by a factor of over 20. We rule out
explanations based on magnetic contaminants, instrument artifacts, and orbital
diamagnetism. The magnetic data are inconsistent with any known physical
phenomena except for granular superconductivity. The present results suggest
the existence of an unknown new physical phenomenon or superconductivity with
an ultra-high transition temperature.
