Interação Kondo e seu Impacto na Frustração

Abstract

Several studies in physics are interested in the magnetic behaviors of materials, for example the magnetocaloric effect and phase transitions, which can be studied in sistems with geometric spin frustration. Frustration in a magnetic system occurs when it is not possible to minimize all contributions to potential energy simultaneously, in particular, when the cause of this is the geometry of the spin lattice, such a situation is called geometric frustration (FG), thus generating interesting contributions to several areas, such as neural networks. Furthermore, the Kondo interaction is also of interest, which contributes in the areas of heavy fermions and quantum dots. The Kondo effect occurs when there is shielding of localized moments due to the coupling between the spins of conduction electrons and localized electrons, which can affect frustrated interactions. Therefore, the objective was to study what can happen to a frustrated lattice in the presence of Kondo interaction. For this purpose, a triangular lattice was adopted as a model with conduction electrons that perform the Kondo interaction, and anisotropic antiferromagnetic (AF) interactions between neighboring first spins of localized electrons, which lead to FG. To solve this problem, Mean Field Theory with Clusters was used, in which the effective system is a triangular cluster of three spin sites with a single conduction electron. The Hamiltonian of this effective system is described by a part of intra-cluster interactions (solved by exact Diagonalization) and another between clusters, the latter approximated by mean fields that lead to self-consistent equations. At low temperatures (T = 0.05) the FG dominates under the effects of thermal fluctuations, thus causing the system to present a frustrated AF phase, but when increasing T it presents a transition to the paramagnetic phase, in which the critical temperature increases with the intensity of the exchange parameter J_{AF}, and decreases with the increase in K_{AF}, thus highlighting the competitive nature between these two parameters and temperature.