THE 1 D EXPANSION FOR LOW-DIMENSIONAL CLASSICAL MAGNETS/

The physical characteristics of two-dimensional classical ferro- and a ntiferromagnets have been calculated in the whole temperature range by an analytical approach based on the expansion in powers of 1/D, where D is the number of spin components. This approach works rather well s ince it yields exact results for antiferromagnetic susceptibility and specific heat at T=0 already in the first order in 1/D and it is consi stent with HTSE at high temperatures. For the quantities singular at T = 0, such as ferromagnetic susceptibility and correlation length, the 1/D expansion supports their general-D functional form in the low-tem perature range obtained by Fukugita and Oyanagi. The critical index et a calculated in the first order in 1/D proves to be temperature depend ent: eta = 2theta/(piD) (theta = T/T(c)(MFT), T(c)(MFT) = J0/D, J0 is the zero Fourier component of the exchange interaction).