Dimensionality effects on the multicritical phase diagrams of the Blume–Emery–Griffiths model with repulsive biquadratic coupling: Mean-field and renormalization-group studies

Six new phase diagrams, including a novel multicritical topology and two new ordered phases, are obtained by the global mean-field theory of the spin-1 Ising model with only nearest-neighbor interactions, for negative biquadratic couplings. Renormalization-group studies indicate a threshold spatial dimension, above and below which different sequences of phase diagrams occur.