Tricritical to mean-field crossover at the spin-peierls transition in (formula presented)

The spin-Peierls phase transition in (Formula presented) has been extensively studied utilizing a variety of experimental techniques. Interpretations of the phase transition behavior vary from tricritical to mean field to Ising critical to (Formula presented) critical. We show that the behavior in the vicinity of the phase transition of each of the order parameters, the magnetic energy gap, and the heat capacity can be quantitatively fitted with few adjustable parameters with a mean-field model incorporating a tricritical to mean-field crossover in the transition region.