Properties of Pt-supported Co nanomagnets from relativistic density functional theory calculations

The electronic, structural, and magnetic properties of Co-based low-dimensional nanostructures supported by Pt surfaces are investigated using computer simulations based on density functional theory. The effects of the local orientation of the magnetization, including the magnetic anisotropy energy, are accounted for within a noncollinear spin-density functional theory formalism where the spin-orbit interaction is described by fully relativistic ultrasoft pseudopotentials. The magnetic moments, the direction of the easy-magnetization axis, and the anisotropy energy are compared with available experimental and theoretical data, and are shown to be extremely sensitive to the local atomic environment of the Co adatoms. We argue that this sensitivity could be exploited to tailor the properties of magnetic devices by engineering the local environment and/or the operating conditions of nanomagnets.

Figure 1

(Color online) Super cells used to describe the Co nanostructures supported by Pt surfaces: (a) Co adatom on Pt(111), (b) Co nanowire on Pt(111), and (c) Co nanowire on Pt(442). Light gray spheres represent the surface Pt atoms while blue (dark gray) spheres represent the supported Co atoms.

Figure 2

(Color online) (a) Equilibrium and (b) unrelaxed adsorption geometries of a Co adatom on a Pt (111) surface. Red (gray) arrows indicate the Co-Pt bond lengths in angstrom while black arrows represent the magnetic moments directed along the easy-magnetization axis in units of ${\mu }_B$. Atoms are represented as described in Fig. 1.

Figure 3

(Color online) Relaxed (top) and unrelaxed (bottom) configurations of a Co nanowire supported by a Pt (111) surface. Panels (a) and (d): Co-Pt bond lengths expressed in $\text{Å}$. Panels (b) and (e): Magnetic moments directed along the easy-magnetization axis in units of ${\mu }_B$. [Note in panel (b) the arrow is oriented parallel to the wire.] Panels (c) and (f): Total energy as a function of the Co magnetic-moment direction expressed in terms of the angles $\theta$ and $\varphi$ defined in the inset. Atoms are represented as described in Fig. 1.

Figure 4

(Color online) Relaxed (top) and unrelaxed (bottom) configurations of a Co nanowire supported by a Pt (442) surface. Panels (a) and (d): Co-Pt bond lengths expressed in angstrom. Panels (b) and (e): Magnetic moments directed along the easy-magnetization axis in units of ${\mu }_B$. Panels (c) and (f): Total energy as a function of the Co magnetic-moment direction expressed in terms of the angles $\theta$ and $\varphi$ defined in the inset. Atoms are represented as described in Fig. 1.