Magnetic Susceptibility of Bromine-Graphite

Bromine, even in small quantities, is known to alter very radically properties of graphite such as conductivity, Hall effect, and others. In particular, the relatively large diamagnetic susceptibility of graphite is rapidly decreased by addition of bromine and the effect cannot be explained by assuming presence of bromine in either molecular or atomic form. It appears that this effect can be interpreted in terms of the Brillouin zone structure of graphite. Using Peierls' theory of diamagnetism of free electrons in a solid and Wallace's results concerning the band structure of graphite an expression is derived which relates the change in the magnetic susceptibility to the change in the number of electrons in the Brillouin zones. The theory is in good agreement with experiment if the effectiveness of bromine in accepting electrons is assumed to be that obtained from Hall effect and conductivity data. The probable influence of lattice imperfections is briefly considered.