Large anisotropy of the electrical conductivity of graphite

Graphite is a hexagonal crystal with a perfect basal cleavage. The carbon atoms in it are arranged in layers parallel to the basal plane, the atoms in each layer forming a regular hexagonal net-work . The distance between adjacent layers is 3.4 Å, which is much larger than the distance between adjacent atoms in the same layer, namely, 1.42 Å. The crystal exhibits some remarkable magnetic properties. Whereas its susceptibility along directions in the basal plane is about - 0.5 × 10-6 per gm., which is nearly that of diamond, the susceptibility along the normal to the plane is more than forty times greater, being equal to -22 ×10-6 per gm. at room temperature. The abnormal diamagnetism along the latter direction shows a striking temperature dependence, and is structure-sensitive