Phase transitions in Ising square antiferromagnets with first- and second-neighbour interactions

J L Moran-Lopez, F Aguilera-Granja, J M Sanchez
1994 Journal of Physics: Condensed Matter  
The phase transitions occurring in the king square antiferromagnet with fim-(31) and second-( 1 2 ) nearest-neighbour interactions are studied using several mean-field approximations and for a wide range of R = 32/31, The largest approximation used corresponds to a ninepoint cluster approximation of the cluster variation method. In this w e , the hansition temperatures as a function of R are found to be in excellent agreement with those obtained by othex methods. The mean-field approximations
more » ... ld approximations predict a first-order transition in the range 0.5 c R 5 1.2. where the critical exponents associated with the paramagnetic to superantifemmagnetic transition have been reported to vary continuously with R. In that range of R, the mean-field approximations also predict a crossover W e e n two distinct instabiliiy tempera-, or spinodals, taking place immediately below the first-order transition. Mean-field results are also given for the magnetization m, the specific heat C,. the magnetic susceptibility x1 the staggered susceptibility x3, and the pair correlation function uij between i and j sites. 14645, and by Consejo Naciond de Ciencia y Tecnologfa through gants C90-07-0383 and 1774-E9210. A 165 266 Grynberg M D and Tan& B 1992 Phys. Rev. B 45 2816 Blote H W I, Compagner A and Hoogland A 1987 Physiea A 141 375 Stephenson J 1970 Phys. Rev. B 1 4405 Kikuchi R 1951 Phys. Rev. 81 988 Bragg W L and Williams E J 1934 Proc. R. Soc. A 145 699 Guggenheim E A 1935 Proc. R. Soc. A 148 304 Bethe H A 1935 Pmc. R. Soc. A 150 552 Peierls R 1936 Pmc. R. Soc. A 154 207 h e r s H A and Wannier G H 1941 Phys. Rev. 60 252; 1941 Phys. Rev. 60 263 Mordn-Upez J Land Sanchez I M 1993 Physica C 210 401 Sanchez J M, DueasieUe F and Gratias D 1984 Physica A 128 334 McCoy B M and Wu T T 1973 Thc Two-dimm'oml king Model (Cambridge, MA: Harvard University Nauenberg and Nienhuis B 1974 Phys. Rev. Lett. 33 944 Ress) p 40
doi:10.1088/0953-8984/6/45/025 fatcat:3rtyqkfq3vbcrae4juto6gvnve