Misfit-Induced Modification of Structure and Magnetism in $\mathbf{O}/\mathrm{Fe}(001)\mathrm{\text{−}}p(1\mathbf{\times }1)$

The geometry of oxygen atoms in hollow sites of Fe nanoislands ($\oslash \approx 1–2\mathrm{nm}$) on Fe(001) is modified by mesoscopic misfit-induced relaxations of the island atoms. Surface x-ray diffraction, scanning tunneling microscopy, and ab initio calculations indicate a 0.3 Å increased adsorption height [0.7 Å versus 0.4 Å in $\mathrm{O}/\mathrm{Fe}(001)\mathrm{\text{−}}p(1\times 1)$] of O atoms going in parallel with a reduced Fe-Fe layer spacing inducing a reduction of the surface magnetic moment ($2.85{\mu }_B$ versus $3.2{\mu }_B$). Our results demonstrate the importance of the mesoscopic misfit for surface physical properties in general.

Figure 1

Constant current ($U=-0.2\mathrm{V}$ sample bias, $I=100\mathrm{pA}$) STM image ($8\times 3.6{\mathrm{nm}}^2$) showing two differently sized Fe nanoislands deposited on $\mathrm{O}/\mathrm{Fe}(001)\mathrm{\text{−}}p(1\times 1)$. The profile along the line is shown in the inset.

Figure 2

(a), (b): Experimental (symbols) and calculated (lines) structure factor amplitudes along two CTRs for $\mathrm{O}/\mathrm{Fe}(001)\mathrm{\text{−}}p(1\times 1)$ (squares) and 0.5 ML Fe on $\mathrm{O}/\mathrm{Fe}(001)\mathrm{\text{−}}p(1\times 1)$ (circles). The dashed red line corresponds to the calculated $\mid F\mid$’s assuming a hypothetical pure island-rim structure. (c), (d): Contour plots of GOF versus oxygen adsorption heights and first Fe-Fe interlayer spacings at the rim and terrace structures. Labels refer to Fig. 3a. The cross marks the minimum. The contour level spacing relative to the minimum ($\mathrm{GOF}=1.2$) is indicated.

Figure 3

(a) Model for 0.5 ML of Fe on $\mathrm{O}/\mathrm{Fe}(001)\mathrm{\text{−}}p(1\times 1)$ showing the terrace (left) and the island (right) structure. Numbers represent distances in angstrom units. Interatomic distances: ${\mathrm{O}}_r\mathrm{\text{−}}{\mathrm{Fe}}_t$, 2.12 Å; ${\mathrm{O}}_r\mathrm{\text{−}}{\mathrm{Fe}}_r$, 2.14 Å; ${\mathrm{O}}_t\mathrm{\text{−}}{\mathrm{Fe}}_b$, 2.04 Å; ${\mathrm{O}}_t\mathrm{\text{−}}{\mathrm{Fe}}_t$, 2.07 Å. (b) A $20\times 10{\mathrm{nm}}^2$ STM image of 0.6 ML $\mathrm{Fe}/\mathrm{O}/\mathrm{Fe}(001)\mathrm{\text{−}}p(1\times 1)$ showing the approximate morphology of the sample studied by SXRD. (c) Profile along the line in (b).

Figure 4

Calculated geometry of an Fe nanoisland consisting of a terrace structure in the center ($t$) and the rim ($r$) structure similar to that shown in Fig. 1a. Calculated magnetic moments for atoms ${\mathrm{Fe}}_t$ and ${\mathrm{Fe}}_r$ are indicated. Note the largely different length scales along the $x$ and $h$ direction.