Mixed spin-1/2 and spin-1 Ising ferromagnets on a triangular lattice

• We study the mixed spin-1/2 and spin-1 Ising ferromagnets on a triangular lattice.
• Two distinct models are obtained by two different ways of the spin mixing.
• Critical properties of both models are studied by Monte Carlo simulations.
• Phase diagram of one model features both first- and second-order phase transitions.
• No phase transitions occur between two LRO phases in the second model except for T=0T=0.

By Monte Carlo simulations we study critical properties of the mixed spin-1/2 and spin-1 Ising model on a triangular lattice, considering two different ways of the spin-value distributions on the three sublattices: (1/2,1/2,1)(1/2,1/2,1) and (1/2,1,1)(1/2,1,1). In the former case, we find standard Ising universality class phase transitions between paramagnetic and magnetic phases but no phase transitions between two distinct magnetic phases (±1/2,±1/2,±1)(±1/2,±1/2,±1) and (±1/2,±1/2,0)(±1/2,±1/2,0) at any finite temperature, except for some interesting non-critical anomalies displayed by response functions. On the other hand, the latter case turns out to be a rare (or perhaps the only) example of a two-dimensional mixed spin-1/2 and spin-1 Ising model on a standard lattice that displays tricritical behavior.