Eur. Phys. J. B 5, 687-695 (1998)
https://doi.org/10.1007/s100510050492

Mixed spin transverse Ising model with longitudinal random crystal field interactions ^*

¹ Groupe de Mécanique Statistique des Transitions de Phases et Phénomènes Critiques, Laboratoire de Physique Théorique, Université Hassan II, Faculté des Sciences Aîn Chock, BP 5366 Maârif, Casablanca, Morocco
² Institut für Theoretische Physik, Universität zu Köln, Zülpicher Strasse 77, 50937 Köln, Germany

Corresponding author: ^a kluemper@thp.uni-koeln.de

Received: 13 February 1998
Accepted: 17 March 1998
Published online: 15 October 1998

Abstract

The effect of a longitudinal random crystal field interaction on the phase diagrams of the mixed spin transverse Ising model consisting of spin-1/2 and spin-1 is investigated within the finite cluster approximation based on a single-site cluster theory. In order to expand a cluster identity of spin-1, we transform the spin-1 to spin-1/2 representation containing Pauli operators. We derive the state equations applicable to structures with arbitrary coordination number N. The phase diagrams obtained in the case of a honeycomb lattice (N=3) and a simple-cubic lattice (N=6), are qualitatively different and examined in detail. We find that both systems exhibit a variety of interesting features resulting from the fluctuation of the crystal field interactions.