Quenched decorated Ising model in three dimensions

The three-dimensional (3d) quenched decorated Ising model with competitive interactions is treated to simulate the 3d antiferromagnetic phase stabilit y limit of the high-temperature superconductor cuprate compounds (e.g., La- Ba-Cu-O and Y-Ba-Cu-O). The model consists of planes in which the nodal spi ns interact antiferromagnetically (J) with its nearest neighbors and ferrom agnetically (K) with a decorated spin on the bond between them, which is qu enched and randomly distributed over the lattice. By using the framework of an effective-field theory, we discuss the variation of the critical concen tration p(c) where the Neel temperature tends to zero for various values of alpha = J/K. We obtain for alpha < 1/6 the critical concentration p(c) = 0 .0297 in excellent accordance with experimental result p(c) = 0.0250 of the La2-xBaxCuO4 (x = 2p) compound (2-1-4). Whereas for the YBa2Cu3O6+x compou nd (1-2-3) we have obtained a better value p(c) = 0.1588 (p(c)(exp) = 0.20) for alpha =1/2 Comparison with the experimental result of the phase diagra m also was presented, and it is qualitatively in accordance only for the 1- 2-3 compound. (C) 2000 Elsevier Science B.V. All rights reserved.