Electronic and magnetic properties of Co and Ni impurities in Cu wires: first-principles investigation of local moment formation in one dimension

Abstract

"The local moment formation in one-dimensional (1D) systems is investigated in the framework of a generalized gradient approximation to density-functional theory (DFT). The electronic and magnetic properties of Co and Ni impurities in finite Cu wires are determined as a function of experimentally relevant parameters such as wire length, impurity-host distance, impurity position within the wire, and total spin polarization S-z. Results are given for the interatomic equilibrium distances, relative stability of different total spin configurations, local magnetic moments in both Wigner-Seitz and Bader cells, electronic density of states at the impurity, and induced magnetic moments in the 1D metal including their coupling with the impurity. The calculations show that the optimal total spin polarization is one above the minimal value. In fact, for chains having an even number of Cu atoms, the ground-state total spin is S-z = 1 for Ni-doped wires and S-z = 3/2 for Co-doped wires. Both Co and Ni impurities preserve their magnetic degree of freedom and develop large local magnetic moments in all low-lying spin configurations (S-z <= 5/2). These almost completely saturated impurity moments are largely dominated by the d-electron contributions. In the ground-state the magnetic coupling between the impurity and the induced moments at the host atoms is ferromagneticlike. Thus, the local exchange energy dominates over hybridization and spin-fluctuation effects, at least in the framework of the present approximation to DFT. The local density of electronic states (LDOS) at the impurity is found to have essentially d character in the whole valence-band range. Large exchange splittings consistent with saturated d moments are observed, which imply a full minority-spin polarization of the LDOS at the Fermi energy epsilon(F). A remarkable correlation is revealed between the rotational symmetry and the degree of delocalization of the impurity states close to epsilon(F). Trends as a function of the local atomic environment are discussed."