Anomalous Behavior of the Zero Field Susceptibility of the Ising Model   on the Cayley Tree
  It is found that the zero field susceptibility chi of the Ising model on the Cayley tree exhibits unusually weak divergence at the critical point Tc. The susceptibility amplitude is found to diverge at Tc proportionally to the tree generation level n, while the behavior of chi is otherwise analytic in the vicinity of Tc, with the critical exponent gamma=0. 
Tatijana Stosic, Borko D. Stosic and Ivon P. Fittipaldi