Order-from-disorder effect in the exactly solved mixed spin-(1/2, 1) Ising model on fully frustrated triangles-in-triangles lattices

TL;DR

This paper exactly solves a frustrated mixed spin-(1/2, 1) Ising model on complex lattices, revealing how frustration and anisotropy induce diverse ordered and disordered states, including reentrant phase transitions and order-from-disorder effects.

Contribution

It provides an exact solution for the mixed spin-(1/2, 1) Ising model on frustrated lattices, uncovering novel critical phenomena and coexistence of order and disorder.

Findings

Discovery of order-from-disorder effect in the model

Identification of reentrant phase transitions with multiple critical points

Evidence of coexistence of long-range order and partial disorder

Abstract

The mixed spin-(1/2, 1) Ising model on two fully frustrated triangles-in-triangles lattices is exactly solved with the help of the generalized star-triangle transformation, which establishes a rigorous mapping correspondence with the equivalent spin-1/2 Ising model on a triangular lattice. It is shown that the mutual interplay between the spin frustration and single-ion anisotropy gives rise to various spontaneously ordered and disordered ground states, which differ mainly in an occurrence probability of the non-magnetic spin state of the integer-valued decorating spins. We have convincingly evidenced a possible coexistence of the spontaneous long-range order with a partial disorder within the striking ordered-disordered ground state, which manifest itself through a non-trivial criticality at finite temperatures as well. A rather rich critical behaviour including the order-from-disorder effect and reentrant phase transitions with either two or three successive critical points is also found.