Low Temperature Behavior of a Pure Dipole-Dipole System

The Van Vleck moment expansion is applied to a pure dipole system. On the basis of the long range nature of the forces sequences of diagrams are selected that give the dominant contributions in the lattice sums. A selection of diagrams contributing to the entropy and susceptibility are displayed. There are three different summations to be performed for each type of diagram: the trace over the spin variables; the lattice summation and the summation over the Cartesian coordinates. The second was performed on the computer and the last summation was obtained by means of the Kramers-Wannier diagonalization. In order to obtain the contributions of diagrams of higher order a Fourier transform was employed. The calculations were performed for Cerous Magnesium Nitrate using a g-factor that is zero along the c-axis. The results are compared with experiments. (Author) Doctoral thesis.