FINITE-SIZE EFFECTS IN LAYERED MAGNETIC SYSTEMS

Thermal and magnetic effects in a system consisting of thin layers of coupled Ising spins with S=1/2 and S=1 are considered. The specific he at and the correlation length display maxima at two different temperat ures. It is discussed in what sense these maxima can be interpreted as a finite-size rounding of a thermodynamic singularity associated with a phase transition. The connection with ordinary, extraordinary, and special surface phase transitions is made. In two dimensions (2D), the surface critical exponents are calculated from conformal invariance. The bulk and surface finite-size scaling of the order-parameter profil es at the transition points is discussed. In 2D, an exact scaling func tion for the profiles is suggested through conformal invariance argume nts for the (extra)ordinary transition.