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We study the dynamical properties of the fully frustrated Ising model. Due to the absence of disorder the model, contrary to spin glass, does not exhibit any Griffiths phase, which has been associated to non-exponential relaxation dynamics. Nevertheless we find numerically that the model exhibits a stretched exponential behavior below a temperature T_p corresponding to the percolation transition of the Kasteleyn-Fortuin clusters. We have also found that the critical behavior of this clusters for a fully frustrated q-state spin model at the percolation threshold is strongly affected by frustration. In fact while in absence of frustration the q=1 limit gives random percolation, in presence of frustration the critical behavior is in the same universality class of the ferromagnetic q=1/2-state Potts model., 7 pages, RevTeX, 11 figs, to appear on Physical Review E

We present a simple argument, valid in all dimensions for a wide range of quenched dilute spin models, for the equality of the pair correlation function and the pair connectedness function at the point p = pc, T = 0 is approached along the T axis.

We discuss the temperature-concentration (T−x) phase diagram of La 2−x (Sr 1 Ba) x CuO 4 . The magnetic interactions of the hole spins with the Cu spins yield frustration, explaining the fast decrease in the Ne´el temperature and yielding a new spin glass phase. The same interactions yield a strong attractive hole-hole potential, which can lead to pairing and superconductivity.

We show that the exponent which describes crossover between d -and ( d −1)-dimensional percolation in an anisotropic system equals the mean-size exponent of the ( d -dimensional system. This situation is analogous to crossover behaviour in anisotropic thermal critical phenomena.