Magnetism of a Co monolayer on Pt(111) capped by overlayers of 5d elements: A spin-model study

Abstract

Using first-principles calculations, we study the magnetic properties of a Co monolayer on a Pt(111) surface with a capping monolayer of selected 5d elements (Re, Os, Ir, Pt and Au). First we determine the tensorial exchange interactions and magnetic anisotropies characterizing the Co monolayer for all considered systems. We find a close relationship between the magnetic moment of the Co atoms and the nearest-neighbor isotropic exchange interaction, which is attributed to the electronic hybridization between the Co and the capping layers, in spirit of the Stoner picture of ferromagnetism. The Dzyaloshinskii-Moriya interaction is decreased for all overlayers compared to the uncapped Co/Pt(111) system, while even the sign of the Dzyaloshinskii-Moriya interaction changes in case of the Ir overlayer. We conclude that the variation of the Dzyaloshinskii-Moriya interaction is well correlated with the change of the magnetic anisotropy energy and of the orbital moment anisotropy. The unique influence of the Ir overlayer on the Dzyaloshinskii-Moriya interaction is traced by scaling the strength of the spin-orbit coupling of the Ir atoms in Ir/Co/Pt(111) and by changing the Ir concentration in the Au1−xIrx/Co/Pt(111) system. Our spin dynamics simulations indicate that the magnetic ground state of Re/Co/Pt(111) thin film is a spin spiral with a tilted normal vector, while the other systems are ferromagnetic. arXiv:1801.09426v1 [cond-mat.mtrl-sci]

Comparison of first-principles methods to extract magnetic parameters in ultrathin films: Co/Pt(111)

“…Indeed, if we perform a linear fit to the KKR-derived DMI energies in an interval of |q| ≤ 0.1 2π a , similarly to the procedure used for FLAPW-gBT calculations, we obtain an identical spiralization (up to two digits) as compared to the FLAPW-gBT calculations. Simon et al 16 use an analogous fitting-procedure with pair-interaction parameters as calculated by the KKR method, employing a different code, and obtain a value in perfect agreement to our KKR-derived values (see Table III).…”

“…the discussion in Ref. 16). Here, we take t Co = 0.2 nm as thickness of the monolayer (see Table I).…”

“…Both stacking positions of Co on the Pt(111) substrate (fcc or hcp) are considered. KKR-values in parentheses are obtained by an alternative evaluation method, which employs fitting of spin-spiral energies (see text and Ref 16…”

Spin-spiral formalism based on the multiple-scattering Green's function technique with applications to ultrathin magnetic films and multilayers

“…According to Ref. [51], the effective spinmodel parameters for C 3v point group symmetry are defined as…”

“…In the present case we use the same sign convention as in Ref. [51], namely, D > 0 corresponds to the left-handed (counterclockwise) rotational direction, while D < 0 to the right-handed (clockwise) rotational direction. The effective spin-model parameters can obviously determined from the long-wavelength (small-wavenumber) limit of the spin-wave spectrum: J eff is related to the curvature of the non-relativistic energy dispersion, while D eff to the slope of the SO induced contribution at q = 0.…”