  We found that numbers of fully connected clusters in Barab\'asi-Albert (BA)
networks follow the exponential distribution with the characteristic exponent
$\kappa=2/m$. The critical temperature for the Ising model on the BA network is
determined by the critical temperature of the largest fully connected cluster
within the network. The result explains the logarithmic dependence of the
critical temperature on the size of the network $N$.

Statistical Mechanics;Disordered Systems and Neural Networks