No abstract

First-principles calculations in the framework of the generalized gradient approximation together with U on-site Coulomb corrections in the GGA + U approach to density functional theory (DFT) are performed to investigate the structural stability, magnetic order, and magnetocrystalline anisotropy of one-dimensional (1D) cobalt-oxide chains on Rh(553) step-surfaces. We found that the chains' magnetic and structural stability strongly depends on the oxygen concentration, η. It is determined that there exist competing direct ferromagnetic and indirect antiferromagnetic exchange interactions in the dopedoxygen 1D linear chains, and in general, the oxygen doping stabilizes the antiferromagnetism. For pure Co linear chains and low oxygen concentrations, in which η ≤ 0.1 monolayers (ML), the ferromagnetic solution is the ground-state magnetic configuration. For η > 0.2 ML, the antiferromagnetic arrangement stabilizes through superexchange interactions. The strong influence regarding the oxygen-doping on the Co linear chains' structural properties is evidenced when a small dimerization between the Co atoms at low O concentrations emerges. In contrast, dimerization in the Co chains is suppressed when the system is "oxygen-free" or η > 0.2 ML. The increase of oxygen concentration strengthens the pd hybridization between Co d-states and O p-states, leading to an electronic redistribution of the majority and minority bands of the Co d-states. Such a redistribution yields to the formation of more localized bands. A significant reduction of the local magnetic moment in the Co atoms is followed. The robustness of the DFT + U results is also discussed to some extent. Throughout a perturbative analysis, we also investigate the oxygen dependence on the magnetocrystalline anisotropy energy (MAE) for the Co-oxide chains, which ranges from 0.4 to 1.2 meV. Interestingly, magnetization directions canted to the wires' direction or perpendicular to the Rh terrace are determined. Their origins are discussed in terms of the local contributions to the MAE.

No abstract

Tailoring the magnetic properties at atomic-scale is essential in the engineering of modern spintronics devices. One of the main concerns in the novel nanostructured materials design is the decrease of the paid energy in the way of functioning, but allowing to switch between different magnetic states with a relative low-cost energy at the same time. Magnetic anisotropy (MA) energy defines the stability of a spin in the preferred direction and is a fundamental variable in magnetization switching processes. Transition-metal wires are known to develop large, stable spin and orbital magnetic moments together with MA energies that are orders of magnitude larger than in the corresponding solids. Different ways of controlling the MA have been exploited such as alloying, surface charging, and external electrical fields. Here we investigate from a first-principle approach together with dynamic calculations, the surface strain driven mechanism to tune the magnetic properties of deposited nanowires. We consider as a prototype system, the monoatomic Co wires deposited on strained Pt(111) and Au(111) surfaces. Our first-principles calculations reveal a monotonic increase/decrease of MA energy under compressive/tensile strain in supported Co wire. Moreover, the spin dynamics studies based on solving the Landau-Lifshitz-Gilbert equation show that the induced surface-strain leads to a substantial decrease of the required external magnetic field magnitude for magnetization switching in Co wire.

We present ab initio study of the magnetic properties of monatomic 3d transition metal (Mn, Fe, Co, Ni) nanowires without and with oxygen atoms on vicinal Rh (553) surface. We considered different experimentally observed submonolayer quantities of oxygen atoms. It was found that monatomic 3d metal nanowires without oxygen are in magnetic states. Within oxidized metal nanowires oxygen atoms affect on the magnetic moments and magnetic interaction of metal atoms. This influence leads to reduced (in the case of Mn, Fe and Co atoms) or quenched (in the case of Ni atoms) magnetic moment for these metal atoms.