Magnetic correlations between two Kondo impurities with two magnetic configurations: Narrow-band limit

The lowest excitation energy and the magnetic correlations < S-1 . S-2 > between two magnetic impurities are analyzed within the two-magnetic-impurity model Hamiltonian. The model includes two magnetic ions that can exist in two valence states and a band of conduction electrons. The two localized states represent the ground states of the ionic configurations (5f)(n) and (5f)(n+1), assumed to be a doublet and a triplet, respectively. In the zero band-width limit, three parameters characterize this model: the energy difference between the magnetic configurations (Delta), the localized-extended-state hybridization energy (V), and the relationship between the Fermi wavelength and the distance (r) over right arrow between the magnetic ions (phi = (k) over right arrow (F) .(r) over right arrow). For phi -> 0, the strong coupling regime takes place and the physics that governs the ground state depends on Delta/V. For V <<-Delta, the highest spin configuration is favored, and the model shows a triplet ground state and the coexistence of strong ferromagnetic (F) correlations between the impurities with the Kondo physics of two magnetic impurities. For V < -Delta, with major charge fluctuations between the magnetic configurations, a singlet ground state occurs and antiferromagnetic (AF) correlations between the impurities appear. When phi increases, the decoupling of the impurities proceeds and < S-1 . S-2 > decreases, finally for phi = pi/2 the decoupled limit takes place and the model is reduced to two independent ions (< S-1 . S-2 > = 0). For a narrow region of Delta/V, when phi increases, the model shows the crossover from singlet (AF) ground state to triplet (F) ground state. (C) 2013 Elsevier B.V. All rights reserved.