${\mathrm{Fe}}_m∕{\mathrm{Au}}_n$ multilayers from first principles

Using the first-principle approach and direct method, the phonon dispersion relations and the stability of the ${\mathrm{Fe}}_m∕{\mathrm{Au}}_n$ multilayers as perfectly ordered structures consisting of Fe(001) and Au(001) monolayers have been studied. The structures with Au and Fe layer thicknesses of two or more monolayers were shown to be stable. Multilayers with either Fe or Au monolayer were found to be unstable, although stable configurations were obtained by rearrangement of the atoms according to soft mode displacements.

Figure 1

The phonon dispersion relations and phonon density of states spectra for the fcc Au and bcc Fe crystals. Experimental points are taken from Refs. 28, 29 for gold and iron, respectively.

Figure 2

The schematic pictures of the different ${\mathrm{Fe}}_m∕{\mathrm{Au}}_n$ multilayers. The black and open circles represent Fe and Au atoms, respectively. The distances between different layers are $d_{\mathrm{Au}\text{−}\mathrm{Au}}=2.07\mathrm{\AA }$, $d_{\mathrm{Fe}\text{−}\mathrm{Au}}=1.73\mathrm{\AA }$, and $d_{\mathrm{Fe}\text{−}\mathrm{Fe}}=1.40\mathrm{\AA }$.

Figure 3

The phonon dispersion relations of the different ${\mathrm{Fe}}_m∕{\mathrm{Au}}_n$ multilayers: (a) ${\mathrm{Fe}}_1∕{\mathrm{Au}}_1$, (b) ${\mathrm{Fe}}_1∕{\mathrm{Au}}_2$, (c) ${\mathrm{Fe}}_1∕{\mathrm{Au}}_3$, (d) ${\mathrm{Fe}}_1∕{\mathrm{Au}}_5$, (e) ${\mathrm{Fe}}_2∕{\mathrm{Au}}_2$, (f) ${\mathrm{Fe}}_2∕{\mathrm{Au}}_4$, (g) ${\mathrm{Fe}}_3∕{\mathrm{Au}}_3$, (h) ${\mathrm{Fe}}_3∕{\mathrm{Au}}_1$.

Figure 4

The phonon density of states spectra for the different ${\mathrm{Fe}}_m∕{\mathrm{Au}}_n$ multilayers. The description of panels (a)–(f) corresponds to those of Fig. 2. The lines and shaded areas describe the total density of states and the Fe partial density of states, respectively.

Figure 5

The phonon dispersion relations and the phonon density of states spectra of the ${\mathrm{Fe}}_1∕{\mathrm{Au}}_1$ (a) and (c) and ${\mathrm{Fe}}_1∕{\mathrm{Au}}_3$ (b) and (d) stable configurations.

Figure 6

The rearrangement of the atoms in each of four layers forming the ${\mathrm{Fe}}_1∕{\mathrm{Au}}_1$ (left column) and ${\mathrm{Fe}}_1∕{\mathrm{Au}}_3$ (right column) structures. Black circles represent Fe atoms, open and black and white circles correspond to the gold atoms. Close to the symbols the $z$ components of atomic position are given.