By using the differential operator technique and the effective field theory scheme we study the tricritical behavior of Heisenberg classical model of spin-1/2 in a random field. The phase diagram in the T-h plane on a square and simple cubic lattice for a cluster with two spins is obtained when the random field is bimodal distributed. : 71.28+d, 71.30+h, 72.10-d.
PACS
In this work we study a disordered binary Ising model on the square lattice. The model system consists of two different particles with spin-1/2 and spin-1, which are randomly distributed on the lattice. It has been considered only spin nearest-neighbor exchange interactions with J > 0. This system can represent a disordered magnetic binary alloy AxB1−x, obtained from the high temperature quenching of a liquid mixture. The results were obtained by the use of Monte Carlo simulations for several lattice sizes L, temperature T and concentration x of ions A with spin-1/2. We found its critical temperature, through the reduced fourth-order Binder cumulant for the several values of the concentration x of particles (spin-1/2, spin-1), and also the magnetization, the susceptibility and the specific heat as a function of temperature T . * Electronic address: dcambui@fisica.ufmt.br † Electronic address: aarruda@fisica.ufmt.br ‡ Electronic address: mgodoy@fisica.ufmt.br
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