2-DIMENSIONAL FRUSTRATED ISING-MODEL WITH 4 PHASES

In this paper we consider a d=2 random Ising system on a square lattic e with nearest neighbor interactions. The disorder is short range corr elated and asymmetry between the vertical and the horizontal direction is admitted. More precisely, the vertical bonds are supposed to be no nrandom while the horizontal bonds alternate: one row of all nonrandom horizontal bonds is followed by one row where they are independent di chotomic random variables. We solve the model using an approximate app roach that replaces the quenched average with an annealed average unde r the constraint that the number of frustrated plaquettes is kept fixe d and equals that of the true system. The surprising fact is that for some choices of the parameters of the model there are three second-ord er phase transitions separating four different phases: antiferromagnet ic, reentrant paramagnetic (glassy?), ferromagnetic, and paramagnetic.