Antiferromagnetism. The Triangular Ising Net

Abstract

In this paper the statistical mechanics of a two-dimensionally infinite set of Ising spins is worked out for the case in which they form either a triangular or a honeycomb arrangement. Results for the honeycomb and the ferromagnetic triangular net differ little from the published ones for the square net (Curie point with logarithmically infinite specific heat). The triangular net with antiferromagnetic interaction is a sample case of antiferromagnetism in a non-fitting lattice. The binding energy comes out to be only one-third of what it is in the ferromagnetic case. The entropy at absolute zero is finite; it equals $S(0)=R\frac{2}{\ensuremath{\pi}}\ensuremath{\int}{0}^{\frac{\ensuremath{\pi}}{3}}\mathrm{ln}(2cos\ensuremath{\omega})d\ensuremath{\omega}=0.3383R$The system is disordered at all temperatures and possesses no Curie point.