First principles theoretical study of complex magnetic order in transition-metal nanowires

The electronic and magnetic properties of one-dimensional (1D) transition-metal (TM) systems are investigated from a first principles theoretical perspective. The development of local magnetic moments and the stability of various collinear and non-collinear spin arrangements are determined in the framework of a generalized gradient approximation to density-functional theory (DFT). Two specific complementary problems are considered. The first one concerns the local moment formation in Cu wires doped with Co and Ni impurities. Recent results as a function of wire length, interatomic distances, impurity position within the wire, and total spin polarization S, are reviewed. It is shown that both Co and Ni impurities preserve their magnetic degree of freedom in monoatomic Cu wires by developing almost saturated local moments in all low-lying total spin configurations (S-z <= 5/2). The impurity moments are largely dominated by the d-electron contributions. In the ground state they couple ferromagnetically with the moments induced at the Cu host atoms. The changes in the spin-density distribution and in the local densities of electronic states are quantified as a function of the position of the impurity position within the wire. In addition, recent results on the ground-state magnetic order in V nanowires are reviewed. The stability of ferromagnetic (FM), antiferromagnetic (AF), and spiral non-collinear (NC) orders is analyzed in terms of the frozen-magnon spectrum. A remarkable transition from FM to NC order is observed as a function of the nearest-neighbor (NN) distance a. The dependence of the single-particle electronic structure of the wire on the wave-vector of the spin-density wave (SDW) is demonstrated. Finally, the role of magnetic anisotropy on the stability of NC order is discussed in the framework of a simple classical spin model. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim