Physical review. B, Condensed matter
Ising models with n>1 : A series-expansion approach
Michael Plischke, J. Oitmaa
Abstract
We investigate the Ising model with nearest-neighbor ferromagnetic and next-nearest-neighbor antiferromagnetic interactions on the square and body-centered-cubic lattices. For $0<\frac{{J}_{1}}{{J}_{2}}<\frac{3}{2}$ on the bcc lattice the model has two nontrivially degenerate ground states and has been conjectured to have $\mathrm{XY}$ ($n=2$) critical exponents. For $\frac{{J}_{1}}{{J}_{2}}=\frac{3}{2}$ there are three degenerate ground states and Heisenberg critical exponents ($n=3$) are expected. We have obtained nine terms in the high-temperature expansion of the staggered susceptibility. For $0<\frac{{J}_{1}}{{J}_{2}}<~1$ we find $\ensuremath{\gamma}=1.25$ ($n=1$). At $\frac{{J}_{1}}{{J}_{2}}=\frac{3}{2}$ the results are not conclusive, but $\ensuremath{\gamma}=1.33$ ($n=2$) is not ruled out by the series analysis whereas $\ensuremath{\gamma}=1.4$ ($n=3$) is not probable. Results for the square lattice are inconclusive.