Couplings and interface effects in binary superlattices

By employing the high-temperature series expansion technique, we have analyzed the phase transition and the critical phenomena of the two-component superlattice, through three models: Ising, XY and Heisenberg. The reduced critical temperature of the system is studied as function of the thickness of the constituents in the unit cell and the exchange interactions in each material and within the interface. A critical value of the interface exchange interaction above which the interface magnetism appears is obtained. A number of characteristic behaviours such as the possibility of existence of a critical length of the unit cell thickness at which the critical temperature of the system remains insensitive to the exchange coupling within interface are reported. The values of the critical exponent γ, associated with the magnetic susceptibility are comparable to the universal ones, in the limit cases when the system is still comparable to an infinite simple cubic lattice. The asymmetry of the structure and the competition of the effects of the exchange couplings, are important for the magnetic properties of the system.