Phase Diagram of Three-Dimensional Site-Random Ising Model

概要

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The three-dimensional site-randorta Ising model consisting of two types of magnetic ions, Aand B, is investigated by means of the exchange ]VIonte Carlo naetltod. The nearest-neighborinteractions are antiferrotnagnetic (AF) for the B-B pair and ferromagnetic (FIN/I) otherwise. Auniform FIVI or AF ordering is fotrnd to exist in a wide range of concentration c of A Tons, incontrast with the bond-randorn Ising rnodel such as the #J model. The phase diagram is ['ound tobe symrnetric on the c -T plane, thotrgh the ratio of the FIN/I bonds to AF ones is asymmetric withrespect to c : 172. Spin configtrrations of' degenerate grotnnd states and their cluster structureare also studied. Even in the system with c : 0.55, there exists only a unique rigid cluster whichincludes atbout 90% of spins and that cluster shows nonvanishing trniform magnetization. Theseresults strongly suggest that the present tnodel has neither a spin glass phase nor an FM-AFtnixed phase, thottgh their existence in a qttite narrow region around c : 172 has not beencompletely excluded yet.
社団法人日本物理学会の論文
1997-01-15