Propriedades magnéticas e termodinâmicas de uma cadeia dupla formada por spins híbridos

Abstract

Over the last decades, several works have been devoted to the investigation of a new class of hybrid spin systems with nodal localized Ising spins and interstitial delocalized electrons. In a diamond-like geometry, this class of models depicts magnetization plateaus and an enhanced magnetocaloric effect. In square lattices geometry, the quantum correlations may lead to ferromagnetic or antiferromagnetic ordering depending on the filling fraction of the delocalized orbitals. In the present work, we study the magnetic and thermodynamic properties of a hybrid spin ladder consisting of Ising spins placed in distinct chains, interacting with each other through a ferromagnetic exchange coupling φ. The interaction between nearest neighbor’s localized spins on the same chain is mediated by a pair of interstitial electrons that may hop between chains with hopping amplitude t obeying Pauli’s Exclusion Principal. The exchange interaction between each localized spins and an interstitial electron is J. The interplay of hopping amplitude and exchange interaction may give rise to a rich phase diagram for the ground state of the system. Such a model may be exactly solvable by using decoration-iteration transformation, transfer matrix method and exact diagonalization. Our results show that quantum correlations betweeen delocalized spins induce an antiferromagnetic coupling between chains that competes with the ferromagnetic exchange coupling. A resulting kinecally-driven frustration is predominant in the regime of low temperatures and large hopping amplitudes. We provide the full ground-state phase diagram as well as the frustration diagram on distinct coupling regimes. The effect of an external magnetic field are also investigated. Further, we determine how the hopping amplitude and an external magnetic field affect different thermodynamics properties of the system, such as total magnetization, specific heat and magnetocaloric rate.