A Monte Carlo investigation of the dependence of spontaneous magnetization on temperature in Ising models of lithium ferrite

Abstract The temperature dependences of the sublattice magnetizations of nearest-neighbour Ising models of lithium ferrite have been calculated by the Monte Carlo method. Satisfactory agreement with neutron diffraction measurements is obtained for spin S = 5/2 without invoking the large intra-sublattice interactions which result from mean-field analyses of experimental data. The inter-sublattice interaction is approximately – 2[sdot]1 meV. Estimates of the critical ratios kT N/|J AB| and limT⇁TN- |M B/M A|, where T N is the Neel temperature, M A and M B are the sublattice reduced spontaneous magnetizations and J AB is the inter-sublattice interaction constant, have also been obtained for S = ½,3/2,7/2 and ∞. The results are contrasted with the predictions of Neel's molecular field theory and Smart's Bethe-Ising theory, and the dependence of KT N/|J AB| on S is compared with that deduced for Ising and Heisenberg ferromagnets from high-temperature series expansions.