Spin-dependent electronic and magnetic properties of Co nanostructures onPt(111)studied by spin-resolved scanning tunneling spectroscopy

Abstract

Spin-resolved scanning tunneling spectroscopy measurements at low temperatures were performed for Co nanostructures on $\mathrm{Pt}(111)$. On Co monolayer islands and wires the electronic structure changes on the scale of a few atoms due to the changing local stacking of the Co atoms. First-principles calculations for pseudomorphic fcc and hcp stacked Co monolayers assign the dominant feature in the measured spectra to a $d$-like surface resonance of minority-spin character which shifts in energy because of a different coupling to the Pt substrate. Despite the heterogeneous electronic structure of the Co monolayer, the out-of-plane magnetized domains are clearly observed. While the domain wall width measured on wires is less than $4\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ there is no indication for a change in the magnetization direction for islands with a base length up to fifteen times the domain wall width. Furthermore, the magnetic hysteresis in an ensemble of out-of-plane magnetized Co monolayer as well as double-layer nanostructures was observed. While the coercivity for the monolayer nanostructures is about $0.25\phantom{\rule{0.3em}{0ex}}\mathrm{T}$, double-layer islands show surprisingly large coercivities of more than $2\phantom{\rule{0.3em}{0ex}}\mathrm{T}$.