Figure 1

Representative, $2000\AA \times 2000\AA$ STM image of the surface of a ${\gamma }^{\prime }\mathrm{\text{−}}{\mathrm{Fe}}_4\mathrm{N}(100)$ film. The inset shows the crystalline structure of ${\mathrm{Fe}}_4\mathrm{N}$ with the Fe atoms represented as large (red) spheres and the N atoms as small (blue) spheres.Reuse & Permissions

Figure 2

Atomically resolved STM image of the $(2\times 2)p4gm$ reconstruction of ${\gamma }^{\prime }\mathrm{\text{−}}{\mathrm{Fe}}_4\mathrm{N}(100)$ recorded with sample bias voltage of $+0.3\mathrm{V}$ and tunneling current of 1.2 nA. The unit cell is indicated by the dotted line and the inset reproduces the LEED pattern corresponding to this surface ($Ep=110\mathrm{eV}$).Reuse & Permissions

Figure 3

Azimuthal dependence of the intensity of low energy ion scattering peaks measured with a time of flight technique and corresponding to Ar, N, and Fe recorded on the $(2\times 2)p4gm$ ${\mathrm{Fe}}_4\mathrm{N}(100)$ surface. The experimental data are shown as a thin line (in red), while the thick (blue) line shows the corresponding best fit. The zero in the azimuthal angle corresponds to the $⟨110⟩$ crystallographic direction.Reuse & Permissions

Figure 4

Energy gain per unit cell of a 2D ${\mathrm{Fe}}_4{\mathrm{N}}_2(100)$ layer as a function of the lateral displacement of the Fe atoms, which leads to a $(2\times 2)p4gm$ reconstruction. The starting configuration corresponds to the calculated equilibrium lattice parameter of bulk ${\mathrm{Fe}}_4\mathrm{N}$. The resulting atomic model for the $(2\times 2)p4gm$ reconstructed surface is shown in the upper panels. The N atoms are shown as small (blue) spheres and the Fe atoms as large (red) spheres. The arrows indicate the direction of displacement of the Fe atoms. Notice that the lateral atomic displacements of Fe can be interpreted as rotated squares or else, as alternating dimers.Reuse & Permissions

Figure 5

The two main characteristics of the reconstruction, magnetism and 1D character, are illustrated by: (a) Calculated total energy per unit cell of a 2D ${\mathrm{Fe}}_4{\mathrm{N}}_2(100)$ layer as a function of the magnetic moment per Fe atom. (b) Atomic positions resulting from a calculation in which all the Fe atoms are fixed, except those along one particular row of a 2D ${\mathrm{Fe}}_4{\mathrm{N}}_2(100)$ layer. The Fe atoms (large, red, circles) dimerize to form pairs in a 1D lattice distortion. A superposition of the dimers causes the weaving pattern seen in STM images of the $(2\times 2)p4gm$ reconstruction.Reuse & Permissions