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.