Magnetic Anisotropy of Graphite

Abstract

GRAPHITE is known from the investigations of Owen, Honda and others to exhibit an exceptionally large magnetic anisotropy. The susceptibilities of the natural crystal along its hexagonal axis and along perpendicular directions are, according to Honda¹: respectively, per gm., ₁ being thus more than six times ₂ Recently Goetz and his collaborators have found a much higher value for the ratio ₁/₂. Chemically treated pure graphite powder is dispersed by them in a solution of gum Dammar in benzene; the solution is placed in a strong magnetic field and the benzene is allowed to evaporate. All the graphite particles in the solidified medium will then naturally be oriented in the same manner, namely, with their hexagonal axes normal to the direction of the imposed field. From susceptibility measurements on this medium they found² for ₁/₂ a value of 13.2. Later³, using graphite particles dispersed in this manner in a solidified solution of agar, they obtained a still higher value, namely, 18. Their more recent estimate⁴, obtained from a similar suspension of graphite particles in gelatine, is so high as 28. It would thus seem desirable to determine the anisotropy of graphite by an independent method.