Frustrated mixed spin-1/2 and spin-1 Ising ferrimagnets on a triangular lattice

TL;DR

This study uses Monte Carlo simulations to analyze phase transitions and tricritical points in frustrated mixed spin-1/2 and spin-1 Ising ferrimagnets on a triangular lattice, revealing complex critical behaviors due to geometrical frustration.

Contribution

It provides the first detailed Monte Carlo analysis of phase diagrams and tricritical behavior in these specific frustrated ferrimagnetic models.

Findings

Second-order transitions follow Ising universality class.

Presence of tricritical points where transitions switch from second to first order.

Identification of phase boundaries and critical endpoints.

Abstract

Mixed spin-1/2 and spin-1 Ising ferrimagnets on a triangular lattice with sublattices A, B and C are studied for two spin value distributions $(S_{\rm A},S_{\rm B},S_{\rm C})=(1/2,1/2,1)$ and $(1/2,1,1)$ by Monte Carlo simulations. The non-bipartite character of the lattice induces geometrical frustration in both systems, which leads to the critical behavior rather different from their ferromagnetic counterparts. We confirm second-order phase transitions belonging to the standard Ising universality class occurring at higher temperatures, however, in both models these change at tricritical points (TCP) to first-order transitions at lower temperatures. In the model $(1/2,1/2,1)$, TCP occurs on the boundary between paramagnetic and ferrimagnetic $(\pm 1/2,\pm 1/2,\mp 1)$ phases. The boundary between two ferrimagnetic phases $(\pm 1/2,\pm 1/2,\mp 1)$ and $(\pm 1/2,\mp 1/2,0)$ at lower temperatures is always first order and it is joined by a line of second-order phase transitions between the paramagnetic and the ferrimagnetic $(\pm 1/2,\mp 1/2,0)$ phases at a critical endpoint. The tricritical behavior is also confirmed in the model $(1/2,1,1)$ on the boundary between the paramagnetic and ferrimagnetic $(0,\pm 1,\mp 1)$ phases.