Ordered Surface Alloy of Bulk-Immiscible Components Stabilized by Magnetism

Abstract

Using scanning tunneling microscopy and a diffraction experiment, we have discovered a new ordered surface alloy made out of two bulk-immiscible components, Fe and Au, deposited on a Ru(0001) substrate. In such a system, substrate-mediated strain interactions are believed to provide the main driving force for mixing. However, spin-polarized ab initio calculations show that the most stable structures are always the ones with the highest magnetic moment per Fe atom and not the ones minimizing the surface stress, in remarkable agreement with the observations. This opens up novel possibilities for creating materials with unique properties of relevance to device applications.

Anomalous temperature dependence of antistripe width in the annealing of submonolayer Fe on Ru(0001)

“…We find that at both coverages, 0.5 and 0.7 ML, the antistripes widen with increasing temperature, suggesting it is not the property of a special coverage but the general character of the Fe on Ru(0001) system. As in the ML region Fe starts intermixing with the Ru substrate at around 700 K, 15 we suspect that this anomaly is related to the surface alloy and amorphization; in particular, they could be temperature dependent.…”

“…When Fe is deposited on the Ru(0001) substrate, there is about 8.3% tensile lattice mismatch, which gives rise to large surface stress and very likely two-dimensional patterns. It was reported that Fe can mix with the Ru(0001) substrate through random exchange when the annealing temperature is higher than 700 K. 15 So it could be a candidate to study the temperature dependence of the two-dimensional patterns formed by surface alloys.…”

Magnetism of surface alloys of the type MxN1−x/Rh(111)

“…The role of magnetism on the mixing property of surface alloys is important, as has been found in a recent work on Fe-Au/ Ru(0 0 0 1) [23]. The authors found that magnetism, rather than the (hitherto considered) stress relief, was the principal driving force that stabilized the surface alloy of Fe-Au on Ru(0 0 0 1).…”

“…Surface alloying is governed by differences in the surface energy of the components, and also by the surface stress which couples with the size mismatch between the alloy components. The presence of magnetism has also been recently found to play a crucial role in surface alloying [23]. The combined effects of reduced dimensionality, reduced coordination, adsorbate-substrate coupling and surface alloying can lead to intriguing outcomes, and there seems to be a very complex interplay between structure, dimensionality and magnetism.…”

Anomalous random correlations of force constants on the lattice dynamical properties of disordered Au-Fe alloys

“…Although fcc is a high-temperature phase, Au-Fe alloys up to 53 at.%Fe are reported to be easily stabilized at room temperature. [11][12][13][14]Due to sensitivity of magnetic and chemical properties to annealing temperatures, these alloys require at most care in their synthesis, especially as disorder is quite common and difficult to control. Hence, chemical disorder plays an important role in their anomalous structural and magnetic properties.…”