Real-space renormalization group investigation of pure and disordered mixed spin Ising models ond-dimensional lattices |
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Authors: | N. Benayad |
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Affiliation: | (1) Institut für Theoretische Physik, Universität zu Köln, D-5000 Köln 41, Federal Republic of Germany;(2) Present address: Faculté des Sciences I, Univérsité Hassan II, Casablanca, Morocco;(3) Laboratoire de Magnétisme, Université de Rabat, Morocco |
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Abstract: | The mixed spin Ising model (spins =1/2 andS=1) ond-dimensional hypercubic lattices with nearest-neighbour exchange interactions is studied via a renormalization group transformation in position space. The phase diagrams in (L, K) space, i.e. in dependence of the bilinear (K) and the biquadratic (L) interaction coefficients, are qualitatively different ford=2 andd>2. For any dimensiond however it is found that all transitions are of second order. At zero-temperature (K=,L=), the ferromagnetic order disappears at (L/K)0=2, which does not depend ond. Using an extension of this real-space renormalization group analysis we study the two-dimensional random disordered version of the above model.L is kept homogeneous and the bilinear interactionsKij are assumed to be independent random variables with distributionP(Kij)=p(Kij–K)+(1–p)(Kij–K); whereK>0. The phase diagrams for different values ofp are obtained. At zero temperature, it is found that in the bond diluted model (=0) the value (L/K)0 depends continuously onp, whereas in the random ±K interactions (=–1) (L/K)0 is unique and does not depend onp.Supported by the agreement of cooperation between the DFGW. Germany and the CNR-Maroc |
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