Thermodynamical properties ofthe random !eld mixed spin Ising model
N. Benayad ∗ , A. Fathi, L. Khaya
Groupe de M ecanique Statistique, Laboratoire de Physique Th eorique, Facult e des Sciences, Universit e Hassan II - A!"n Chock, B.P. 5366 Maarif, Casablanca, Morocco
Received 13 April 2001
Abstract
A theoretical study ofa mixed spin Ising system consisting ofspin-1=2 and spin-1 with a random !eld is studied by the use ofthe !nite cluster approximation within the framework ofa single-site cluster theory. In this approach, the phase diagrams and magnetizations are investigated for the simple cubic lattice when the random !eld is bimodally and trimodally distributed. The internal energy, speci!c heat and susceptibility are also calculated for both kinds ofthe probability distributions. c 2001 Elsevier Science B.V. All rights reserved.
PACS: 75.10.Hk; 75.40.Cx; 05.45.−a; 05.70.−a
Keywords: Mixed spins; Random !elds; Phase diagrams; Magnetizations; Speci!c heat;
Susceptibility
1. Introduction
The random !eld Ising model (RFIM) on mono-atomic lattices where the local quenched random !eld H i is assumed to have zero average H i r = 0 and is uncorrelated at di;erent sites has been a subject ofmuch theoretical [1–5] and experimental [6–8]
investigations ofthe statistical physics ofrandom and frustrated systems. This is be- cause it helps to simulate many interesting but complicated problems. The best ex- perimental realization ofan RFIM has been the diluted uniaxial-antiferromagnet in a uniform !eld applied along the spin ordering axis (DAFF) such as Rb 2 Co x Mg 1−x F 4
and Fe x Zn 1−x F 2 in magnetic !eld, which correspond, respectively, to two- and three- dimensional proto-typical systems. It has been shown [9–12] that in the presence of a uniform !eld, the random exchange interactions give rise to local random staggered
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