Electronic and Magnetic Properties of Building Blocks of Mn and Fe Atomic Chains on Nb(110)

Abstract

We present results for the electronic and magnetic structure of Mn and Fe clusters on Nb(110) surface, focusing on building blocks of atomic chains as possible realizations of topological superconductivity. The magnetic ground states of the atomic dimers and most of the monatomic chains are determined by the nearest-neighbor isotropic interaction. To gain physical insight, the dependence on the crystallographic direction as well as on the atomic coordination number is analyzed via an orbital decomposition of this isotropic interaction based on the spin-cluster expansion and the difference in the local density of states between ferromagnetic and antiferromagnetic configurations. A spin-spiral ground state is obtained for Fe chains along the [11¯0] direction as a consequence of the frustration of the isotropic interactions. Here, a flat spin-spiral dispersion relation is identified, which can stabilize spin spirals with various wave vectors together with the magnetic anisotropy. This may lead to the observation of spin spirals of different wave vectors and chiralities in longer chains instead of a unique ground state.

Magnetic ground state of supported monatomic Fe chains from first principles

“…The magnetic ground states derived from the new ab-initio optimization technique are compared to those obtained from spin models parametrized from first principles and the effect of the different kind of spin-spin interactions is discussed. Further applications are presented for Fe chains deposited on the (110) surface of bodycentered cubic (bcc) Nb and on the (0001) surface of hexagonal closed pack (hcp) Re, where spin-spiral ground states are found in agreement with previous theoretical works [25,39] and experiment [4].…”

“…Using the Vienna Ab-initio Simulation Package (VASP) [56] Laszloffy et al [39] found that by putting an Fe adatom on the (110) surface of Nb, the average vertical distance of the atoms in the two uppermost Nb layers decreased to 2.2542 Å from the bulk value of 2.3337 Å , while the vertical distance between the Fe adatom and the closest Nb atoms decreased to 1.9868 Å. In the calculations of atomic clusters of Fe these values were used for the interlayer distances between the uppermost two Nb layers, as well as between the top Nb layer and the first two vacuum layer, in which the Fe atoms were embedded [39], respectively. We adopted this geometry in our present calculations of the Fe chains in terms of the embedding Green's function technique.…”

Relativistic first-principles theory of Yu-Shiba-Rusinov states applied to Mn adatoms and Mn dimers on Nb(110)

“…Here we consider the [1 10] and the [1 11] dimers only. Based both on experiments on short Mn chains on Nb(110) [21] and on ab initio calculations [22] it is suggested that the coupling of the Mn atoms in the [1 10] dimer is ferromagnetic (FM), while in the [1 11] dimer it is antiferromagnetic (AFM).…”

“…The theoretical study of Lászlóffy et al [22] suggests that a slightly noncollinear and/or canted configuration can exist for the dimers in the normal state. The possibility of the formation of such tilted ground states and the lack of split YSR states in the AFM dimer compared to experiments motivated us to study the effect of the noncollinear spin configurations to the YSR states.…”

“…Nevertheless, such big deviations from the AFM spin configuration seem to be unrealistic based on the spin-model simulations of Ref. [22], where for the NN [1 11] dimer a θ 179.5 • was predicted.…”