Akademik Veri Yönetim Sistemi
PHYSICA SCRIPTA, cilt.76, sa.6, ss.597-605, 2007 (SCI-Expanded)
A method in Ising models is presented within the framework of the effective-field theory ( EFT) with correlations. In the present method, we have improved the EFT method by including the correlations between the different spins which emerge when expanding the identities. To do this, we have derived a set of linear equations for the considered system by taking as a basis the thermal averages of a central spin and a perimeter spin at the site i, which is defined within spin identities and differential operator technique. By solving numerically the set of linear equations derived for the Ising system with coordination number q = 3, we have evaluated numerically all spin correlation functions without using a kind of decoupling approximation in the spin system under a longitudinal magnetic field. The effects of the longitudinal magnetic field on magnetic properties of the spin systems are discussed in detail. Numerical results are performed and analyzed for the cases of spin-1/2 in a longitudinal magnetic field and spin- 1 with crystal field in a longitudinal magnetic field, respectively on the honeycomb lattice. A number of interesting phenomena, originating from the external field and temperature have been found.