Eur. Phys. J. B 7, 191-209 (1999)
https://doi.org/10.1007/s100510050605

Theory of site-disordered magnets

¹ University of Amsterdam, Van der Waals-Zeeman Institut, Valckenierstraat 65-67, 1018 XE Amsterdam, The Netherlands
² Institute Lorentz for Theoretical Physics, Leiden University, P.O.B. 9506, 2300 RA Leiden, The Netherlands

Received: 27 April 1998
Revised: 27 July 1998
Accepted: 13 August 1998
Published online: 15 January 1999

Abstract

In realistic spinglasses, such as , and , magnetic atoms are located at random positions. Their couplings are determined by their relative positions. For such systems a field theory is formulated. In certain limits it reduces to the Hopfield model, the Sherrington-Kirkpatrick model, and the Viana-Bray model. The model has a percolation transition, while for RKKY couplings the "concentration scaling" occurs. Within the Gaussian approximation the Ginzburg-Landau expansion is considered in the clusterglass phase, that is to say, for not too small concentrations. Near special points, the prefactor of the cubic term, or the one of the replica-symmetry-breaking quartic term, may go through zero. Around such points new spin glass phases are found.