The boundary between the spin-glass and ferromagnetic states of the bond-random Ising model in the square lattice at T = 0

The bond-random (±J) Ising model in the square lattice is considered in the square cluster approximation. The boundary between the ferromagnetic and spin-glass states at T = 0 is obtained as the transition point from the asymmetric distribution of the effective fields to the symmetric distribution. The concentration of this transition, P_FG is obtained by solving the integral equation for the distribution function of the effective fields.