TRICRITICALITY AND THE BLUME-CAPEL MODEL - A MONTE-CARLO STUDY WITHINTHE MICROCANONICAL ENSEMBLE

The microcanonical partition function Omega(alpha,N)(E) of a three-dim ensional ferromagnetic simple cubic Blume-Capel model is calculated fo r several coupling ratios alpha close to and on the first-order side o f the tricritical point. To this end a single Monte Carlo simulation o f a suitably extended partition function for systems of LxLxL spins wi th L is an element of {8,10,12,14,18} was performed. A finite system a nalog of the latent heat is introduced in order to define a tricritica l point in finite systems as well. An empirical scaling of its coordin ates to the thermodynamic limit yields alpha((t))=2.84479+/-0.00030 fo r the tricritical coupling ratio, and k(B)T((t))/J=1.4182+/-0.0055 for the tricritical transition temperature. The results are compared with values obtained on fee lattices.