By using the differential operator technique and the effective field theory scheme we study the tricritical behavior of Heisenberg classical model of spin-12 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 phase diagram of the Heisenberg ferromagnetic model in the presence of a magnetic random field (we have used bimodal distribution) of spin S=1/2 (quantum case) and S=∞ (classical case) on a simple cubic lattice is studied within the framework of the effective-field theory in finite cluster...