Rise and Fall of Reentrant Phase Transitions in a Coupled Spin-Electron Model on a Doubly Decorated Honeycomb Lattice

Abstract

Phase diagrams and spontaneous magnetization are rigorously calculated for a coupled spin-electron model on a doubly decorated honeycomb lattice, which accounts for a quantum-mechanical hopping of the mobile electrons on decorating sites, the nearest-neighbor Ising coupling between mobile electrons and localized spins, as well as the further-neighbor Ising coupling between the localized spins placed on nodal sites. The spontaneously ordered ferromagnetic phase, spontaneously ordered antiferromagnetic phase and disordered paramagnetic phase emerge in a phase diagram depending on an electron filling of the decorating sites, a relative size of the hopping term and both considered coupling constants. It is evidenced that a nature and size of the further-neighbor Ising coupling between the localized spins basically influences rise and fall of reentrant transitions close to a phase boundary between the paramagnetic phase and both spontaneously ordered phases.

Influence of applied electric and magnetic fields on a thermally-induced reentrance of a coupled spin-electron model on a decorated square lattice

“…In order to clarify the simultaneous effect of an applied electric and magnetic fields accompanied by thermal fluctuations on a stability of reentrance in the coupled spin-electron system, we are mainly interested in analyses of thermal magnetic phase diagrams for various model parameters. From the previous analysis [41,42,55] it is known that the mutual competition in the correlated spin-electron systems can produce magnetic phase transitions with several consecutive critical points from the ordered to disordered phase or vice versa. In addition, the strength and type of interaction between localized Ising spins J has a crucial impact on the character of reentrant magnetic phase transitions with a possible existence of mixed reentrant ones [50].…”