Figure 1

(a) The geometry of our SPEELS experiment. A monochromatic spin-polarized electron beam with a polarization parallel or antiparallel to the sample magnetization ($\overrightarrow{M}$) is scattered along the [001] direction from the Fe(110) monolayer in the remanent state. The degree of polarization $P$, in the present case, is $0.7\pm 0.1$. The scattering angle is kept at ${\theta }_0=80°$. $k_i$ and $k_f$ are the magnitudes of the wave vectors of the incident and scattered electrons, respectively. The inset shows the intensity $I_{\uparrow }$ and $I_{\downarrow }$ SPEELS spectra, as measured for 1 ML $\mathrm{Fe}/\mathrm{W}(110)$ at 120 K, using electrons with energy $E_i=3.8\mathrm{eV}$ at $\Delta K^{\parallel }=1.0{\AA }^{-1}$. The energy resolution is $\Delta E_i=16\mathrm{meV}$. (b) The magnified spectra from the inset in (a). (c) The difference and asymmetry spectra clearly showing the magnon signal.Reuse & Permissions

Figure 2

(a) Series of normalized difference SPEELS $\Delta I$ spectra measured for 1 ML $\mathrm{Fe}/\mathrm{W}(110)$ at 120 K for different $\Delta K^{\parallel }$ values, as denoted. The spectra are offset by 0.05 with respect to each other. Because of the low energy ($E_i=3.8\mathrm{eV}$) of the incident electrons, the parallel wave vector transfer is limited to the value of $1.05{\AA }^{-1}$ (for ${\theta }_0=80°$). The higher wave vector excitations (above $1.0{\AA }^{-1}$) are measured with a higher incident electron energy ($E_i=6.25\mathrm{eV}$) and a lower resolution ($\Delta E=18\mathrm{meV}$). (b) The magnon energy versus parallel wave vector transfer $\Delta K^{\parallel }$, as derived from the peak position in the difference SPEELS spectra observed in (a). Red (or gray) and black curves are fits to the dispersion obtained from the Heisenberg model with and without the anisotropy gap, respectively. The inset shows the 2D surface Brillouin zone of the bcc (110) surface with the states probed along the [001] direction.Reuse & Permissions

Figure 3

Magnon dispersions for the different Fe systems. Black line denotes the parabolic magnon dispersion for the bcc Fe bulk $D\Delta K^{\parallel 2}(1-\beta \Delta K^{\parallel 2})$, with $D\approx 280\mathrm{meV}{\AA }^2$, compiled using the INS data [43]. The dispersions obtained by the SPEELS at RT for the 2 ML $\mathrm{Fe}/\mathrm{W}(110)$, and for 24 ML $\mathrm{Fe}/\mathrm{W}(110)$, are plotted using circles and diamonds, respectively. Squares indicate data for the 1 ML $\mathrm{Fe}/\mathrm{W}(110)$ measured at 120 K. The solid lines are guides to the eye based on the same formula [$D\Delta K^{\parallel 2}(1-\beta \Delta K^{\parallel 2})$], with different $D$ and $\beta$. The relation between the bulk Brillouin zone and the two-dimensional Brillouin zone of the (110) surface (shaded area) is shown in the inset.Reuse & Permissions