Elastic versus inelastic spin-polarized electron scattering from a ferromagnetic surface

Spin-polarized electron energy loss spectroscopy was applied to study the intensity asymmetry upon the reversal of the incident spin polarization of elastically and inelastically scattered polarized electrons from an epitaxial ferromagnetic Fe layer on W(110). The polarization of the incident beam was always collinear with the magnetic moment (magnetization) of the sample, and the asymmetries were measured for two opposite magnetizations of the sample. They allowed extracting the exchange and the spin-orbit components from the measured asymmetry. A strong asymmetry of Stoner excitations in an Fe film on W(110) is observed, as expected, at about 3 eV energy loss. The value of the asymmetry declines but is still observable when the surface is contaminated. The asymmetry of elastic scattering for normal incidence and a 50° detection angle is close to zero in contrast to the Stoner excitation asymmetry (inelastic scattering). However, the asymmetry of elastic scattering increases substantially at two specular geometries with 25° and 72° angles of incidence, compared to the normal incidence, and may be even larger than the asymmetry of Stoner excitations. The sign of elastic scattering asymmetry changes upon the reversal of the sample magnetization, indicating the magnetic origin of this asymmetry, i.e., spin-dependent electron-electron scattering with electron exchange. The calculation of the asymmetry of elastic spin-polarized electron scattering from a spin-dependent surface potential barrier shows a qualitative agreement with the measurements.

Figure 1

Three geometrical arrangements used in this work.

Figure 2

(a) Asymmetry of SPEELS for two geometries and two magnetizations of the sample, (b) exchange component of asymmetry, and (c) spin-orbit component of asymmetry.

Figure 3

The same as in Fig. 2, but for the contaminated surface of Fe film.

Figure 4

Intensity asymmetry of SPEELS at specular geometry with 72° (left) and 25° (right) of incidence.

Figure 5

Exchange and spin-orbit components of asymmetry.

Figure 6

(a) SPEELS spectra of W(110), (b) SPEELS of 2 ML of Fe on W(110), and (c) asymmetry of SPEELS for (a) and (b).

Figure 7

Spin-dependent surface potential barrier (SPB) (a), and combined electron scattering from the surface barrier and the crystal surface (b).

Figure 8

Schematic representation of a surface with surface potential barrier (SPB), ultrathin layer (Fe) deposited on a substrate (W).

Figure 9

Spin-dependent SPB. $x$ axis is directed along the normal to the sample surface; the vertical axis represents the value of the potential. On the positive segment of the $x$ axis the potential assumes a constant value of −15 V inside the metal, the negative segment of the $x$ axis is in a vacuum, and the potential asymptotically tends to zero (vacuum level) at infinity. The potential for the majority electrons (spin-up) is shown as a solid line and for the minority electrons (spin-down) a dashed line.

Figure 10

Dependence of the specular reflection coefficients on the normal component of the electron kinetic energy $E_{\mathrm{normal}}$ for spin-up (solid line) and spin-down (dashed line) electrons from the potential barrier of Fig. 9.

Figure 11

Energy dependence of the spin asymmetry of the specular reflection of electrons from the Fe(110) surface potential barrier. It depends on the normal component of the electron kinetic energy $E_{\mathrm{normal}}$.