An application of Padé approximants to Heisenberg ferromagnetism and antiferromagnetism

The method of successive Padé approximants is applied to the high-temperature series for the susceptibility of Heisenberg systems with nearest-neighbour interactions only. It is concluded that the susceptibility of a ferromagnet diverges near the critical temperature with a law (T —Tc)-r, where r is either exactly 4/3 or indistinguishable from 4/3 by the method used with the power series at present available. The susceptibility of an antiferromagnet is also discussed. The specific heat near the critical point is considered but the results are inconclusive.