Spin-glass transition in a system with competing ferromagnetic and antiferromagnetic interaction

Using the recently developed method of Edwards and Anderson we obtain the free energy for a system of spins interacting with an exchange potential having a distribution in the form of the sum of two Gaussians centered about J0 with widths J. When J 0, the system undergoes a spin-glass transition only, with the ferromagnetic or antiferromagnetic phases absent. When J=0 the system shows no transition in the molecular-field approximation used even though J0 is finite. For very low temperatures and for JJ0 12 the method gives a negative specific heat and magnetic susceptibility. These unphysical results also arose in connection with the negative entropy obtained previously for spin glasses.