High-temperature series expansion of the magnetic susceptibility of extended magnetic systems in a complete computer implementation

The high-temperature series expansion (HTSE) of the susceptibility of Heisenberg magnets is formulated completely in algorithms and implemented in computer programs for the first time. Specifying the system under investigation with respect to the spin S (12,1,…,72) of the magnetic centres, their partial structure and their neighbourhood relationship (first, second, and third neighbours), the susceptibility equation is automatically developed up to the required order as a function of the exchange parameters J1, J2, and J3. The calculations involve drawing of the relevant interaction graphs and computation of the trace of the corresponding spin products as well as the determination of the lattice count. The performance of the HTSE program is demonstrated by analysing the magnetic properties of CrBr3 for T>TC.