Low-dimensional Heisenberg magnets: Riemann zeta function regularization

The Riemann zeta function regularization is employed to extract finite temperature corrections to effective magnetic moment $S^*$ of one- and two-dimensional Heisenberg ferro- and antiferromagnets. Whereas for the one-dimensional ferromagnet we obtain the usual $T^{1/2}$ spin-wave dependence, for the antiferromagnetic chain the dependence is described by a generalized incomplete Riemann function. The quantity $S^*$ determines strong short-range magnetic order in the absence of long-range order, in particular the correlation length. For the one-dimensional ferromagnet, the results are confirmed by the self-consistent spin-wave theory and Monte Carlo simulations by Takahashi et al.