Insights into Magnetic Properties of a Mixed Spin-Electron Model on Decorated Planar Lattices Composed of Half-filled Trigonal Bipyramids

Abstract: A mixed spin-electron model on decorated planar lattices formed by corner-sharing trigonal bipyramids is exactly solved by imposing three mobile electrons per triangular cluster of each bipyramid by means of a generalized decoration-iteration mapping transformation. It is shown that the ground state of the model involves two spontaneously long-range ordered phases, namely, the classical phase with a perfect ferromagnetic arrangement of all particles and the macroscopically degenerate quantum one. The macroscopic degeneracy of the quantum phase lies in chiral degrees of freedom of the mobile electrons. Finite-temperature phase diagrams as well as temperature variations of the spontaneous magnetization, entropy, and specific heat clearly prove that the classical spin-electron arrangement is thermally almost twice more stable than the quantum one for some combinations of the model's parameters.