Phase transitions of the three-dimensional semi-infinite Blume-Emery-Griffiths model, extended to negative biquadratic interactions, are investigated within the framework of the mean-field approximation in comparison with the real-space renormalization-group results found previously. All the possible qualitative types of phase diagrams characterizing phase transitions of the model, including high entropy ferrimagnetic and staggered quadrupolar phases, have been determined. It is shown that such a system can exhibit critical and tricritical behavior on the surface and multicritical points.

• Received 16 September 1996

DOI:https://doi.org/10.1103/PhysRevB.56.11161