High-Temperature Magnetic Susceptibility of Interacting Electrons in a Solid

In this paper we consider a pair of electrons in an energy band which interact through a short-range potential. The scattering amplitude is determined exactly, and the energies of states in which the two particles are bound together are found. The change in the density of two-particle states produced by the interaction is computed and used to calculate the second virial coefficient occurring in the expansion of the logarithm of the partition function in powers of the density. Inclusion of an external magnetic field allows determination of the magnetic susceptibility at high temperatures. The result has a form equivalent to that obtained in Stoner's theory of ferromagnetism, thereby justifying that theory in the high-temperature region and yielding an expression for the molecular-field parameter ${\theta }^{\prime }$.