Electronic, structural and magnetic properties of metal clusters doped with magnetic impurities
The electronic, magnetic and structural properties of simple-metal clusters doped with magnetic impurities are currently a fascinating open problem in nanoscience research that poses a serious challenge for condensed matter theory. Most of the difficulties, and reasons for excitement, originate at the subtle interactions between the localized, strongly correlated magnetic degrees of the impurity and the delocalized valence electrons of the metallic environment. Moreover, in contrast to the solid, the latter are confined within the cluster and therefore their properties depend strongly on size and structure.
First principles calculations on NiCuN-1, CoCuN-1, and NiNaN-1 allow us to understand the trends in the ground state and low-lying states with different spin multiplicities for representative specific materials. Global geometry optimizations within Kohn-Sham density-functional theory show that for N ? 9 atoms the structures of doped clusters are compact with the magnetic ion occupying the most-coordinated atomic position. Putting aside some interesting changes in bond length, the structures resemble rather closely those of the corresponding pure CuN or NaN clusters. These trends reflect the dominant role of the sd hybridizations.
The ground state of NiCuN-1 and CoCuN-1 corresponds to a minimum-spin configuration having Sz = 0 or ½. In addition a tendency to antiferromagnetic correlations between the impurity and the Cu electrons is observed. Varying the total spin moment of the cluster reveals interesting correlations between cluster structure and magnetism. Low-energy spin excitations are found that involve similar energies as isomerizations. Thus, structure and magnetic behavior depend strongly on each other. In sum, transition-metal impurities like Ni or Co preserve their magnetic degree of freedom in small Cu clusters and are therefore good candidates for developing interesting many-body phenomena such as Kondo screening or intermediate valence behavior.
This project is developed in collaboration with Dr. J. L. Ricardo-Chávez from Instituto Potosino de Investigación Científica y Técnica (San Luis Potosí, Mexico) and is supported by the DAAD-CONACyT (Mexico) international exchange program PROALMEX.