Susceptibilities of the antiferromagnet REM model

The linear and non-linear susceptibilities of the two sub-lattices Random Energy Model (REM) allowing antiferromagnetic order is studied as a function of the external field (h) and temperature (T). Due to the competition between external field and the internal exchange field acting on the spins there is a drastic change of the system's behavior as the parameters (h,T) are varied. The behavior of the susceptibilities in low and high fields is very different in that the latter may grow as the temperature decreases. Moreover, the critical region undergoes a substantial enlargement as the external field increases.