Theory of site-disordered magnets

In realistic spinglasses, such as CuMn, AuFe and EuSrS, magnetic atoms are located at random positions. Their couplings are determined by their relati ve positions. For such systems a field theory is formulated. In certain lim its it reduces to the Hopfield model, the Sherrington-Kirkpatrick model; an d the Viana-Bray model. The model has a percolation transition, while for R KKY couplings the "concentration scaling" T-g similar to c occurs. Within t he Gaussian approximation the Ginzburg-Landau expansion is considered in th e clusterglass phase, that is to say, for not too small concentrations. Nea r special points, the prefactor of the cubic term, or the one of the replic a-symmetry-breaking quartic term, may go through aero. Around such points n ew spin glass phases are found.