Spin-polarized LEED Research Articles

Theoretical studies of spin-polarized LEED rotation curves: Clean W(100) and Fe overlayers on W(100).

We present a series of theoretical spin-polarized low-energy-electron-diffraction studies which explore the information that may be extracted from rotation curves. Here the polar angle of incidence of an unpolarized beam is held fixed, and the scattering plane is rotated so the azimuthal angle is scanned. The total intensity of the scattered beam is monitored, along with components of spin polarization in the scattered beam parallel and perpendicular to the scattering plane. Venus and collaborators have reported such data for the clean W(100) surfaces, and this surface covered by (ferromagnetic) Fe overlayers. We explore this system, focusing on the sensitivity of features in the rotation curves to aspects of surface geometry and surface magnetism. We find, for example, the polarization data to be very sensitive to interplanar spacings near the surface. \textcopyright{} 1996 The American Physical Society.

Necessity of self-energy corrections in LEED theory for Xe(111): Comparison between theoretical and experimental spin-polarized LEED data.

An essential problem in calculating the electronic structure of solids is that created by many-body interactions. They cause self-energy corrections which in insulators and semiconductors range up to the width of the fundamental band gap. Angular-dependent intensity and asymmetry profiles measured in spin-polarized low-energy electron diffraction (SPLEED) from Xe(111) clearly show the necessity of the self-energy correction if compared to standard SPLEED calculations. Effects due to the self-energy correction have to be clearly distinguished from effects due to the inner potential. The real part of the inner potential affects the energy and, by refraction at the surface potential barrier, the angles of the incident and the diffracted beams, whereas the self-energy correction is equivalent to a change of the energy of the primary beam only. This qualitative difference is proved in our SPLEED investigations and is used to determine the self-energy correction and the inner potential from angular-dependent profiles. For the self-energy correction we found a value of \ensuremath{\Delta}E=3.0\ifmmode\pm\else\textpm\fi{}1.5 eV and for the real (imaginary) part of the inner potential ${\mathit{V}}_{0\mathit{r}}$=3.0\ifmmode\pm\else\textpm\fi{}1.5 eV (${\mathit{V}}_{0\mathit{i}}$=2.0\ifmmode\pm\else\textpm\fi{}0.5 eV).

Structural and magnetic characterization of thin iron films on a tungsten (001) substrate

The structure and remanent magnetization of iron films of thickness up to 5 monolayers (ML), grown on a tungsten (001) substrate at room temperature, have been characterized. The iron grows pseudomorphically, monolayer-by-monolayer, up to a thickness of 2 ML. Subsequent film growth is disordered, but does not form islands until annealed. One pseudomorphic monolayer is stable upon annealing up to the desorption temperature. Magnetic hysteresis loops of the films (at room temperature) were collected in remanence, by measuring the spin polarization imparted by diffraction to an initially unpolarized electron beam. The films show in-plane ferromagnetism beginning at a thickness between 1.35 ± 0.05 and 1.50 ± 0.06 ML, and have biaxial in-plane anisotropy. The easy axis is most likely along the [10] direction of the film — an easy axis along [11] is possible, but implies an anomalously small anisotropy. The remanent electron spin polarization depends strongly on the magnetic state, and scattering energy and geometry, illustrating the feasibility of using spin-polarized LEED to study the interdependence of magnetic and electronic structure in this system.

Use of spin-polarized LEED rotation curves to study disordered surfaces: W(001)-(1 × 1) and W(001)-2H(1 × 1)

Abstract Extensive data sets of spin-polarized low energy electron diffraction (SPLEED) rotation curves from the clean W(001)−(1 × 1) and hydrogen-saturated W(001)−(1 × 1) and W(001)−2H(1 × 1) surfaces are presented. These represent the first simultaneous LEED measurements of two components of the electron spin polarization and diffracted intensity on any system. These measurements should be more sensitive to the disorder of the surface layer of clean W(001)−(1 × 1) than traditional LEED I–V curves at normal incidence for three reasons: the large scattering angles enhance intralayer scattering relative to interlayer scattering; electron spin polarization measurements are particularly sensitive to intensity minima where diffuse scattering from disorder is relatively important; and the data set is a comparative study of ordered and disordered surfaces. The data are in qualitative agreement with a smaller surface layer contraction and a greater degree of order on the hydrogen-saturated surface compared to the clean surface. These results suggest that detailed SPLEED calculations are justified to test and quantify these indications.

Use of spin-polarized LEED rotation curves to study disordered surfaces: W(001)−(1 × 1) and W(001)−2H(1 × 1)

Extensive data sets of spin-polarized low energy electron diffraction (SPLEED) rotation curves from the clean W(001)−(1 × 1) and hydrogen-saturated W(001)−(1 × 1) and W(001)−2H(1 × 1) surfaces are presented. These represent the first simultaneous LEED measurements of two components of the electron spin polarization and diffracted intensity on any system. These measurements should be more sensitive to the disorder of the surface layer of clean W(001)−(1 × 1) than traditional LEED I–V curves at normal incidence for three reasons: the large scattering angles enhance intralayer scattering relative to interlayer scattering; electron spin polarization measurements are particularly sensitive to intensity minima where diffuse scattering from disorder is relatively important; and the data set is a comparative study of ordered and disordered surfaces. The data are in qualitative agreement with a smaller surface layer contraction and a greater degree of order on the hydrogen-saturated surface compared to the clean surface. These results suggest that detailed SPLEED calculations are justified to test and quantify these indications.

Structural investigations on Xe/Pd(111) with spin-polarized LEED

Abstract (√3 × √3)R30°-Xe/Pd(111) and the dilute phase of Xe/Pd(111) were investigated with spin-polarized low-energy electron diffraction (SPLEED). In the experiment spin-polarized electrons from a GaAs source were scattered and the spin-dependent intensities were measured. Comparative calculations were carried out by means of a relativistic LEED program. The structure determination of (√3 × √3)R30°-Xe/Pd(111) yields a layer distance of 3.5 ± 0.1 A , the Xe atoms being adsorbed in hollow sites. In the dilute phase of Xe/Pd(111) the adsorbed Xe atoms occupy on-top sites with a Xe-Pd distance of 4.0 ± 0.1 A without two-dimensional periodicity.

Structural investigations on Xe/Pd(111) with spin-polarized LEED

(√3 × √3)R30°-Xe/Pd(111) and the dilute phase of Xe/Pd(111) were investigated with spin-polarized low-energy electron diffraction (SPLEED). In the experiment spin-polarized electrons from a GaAs source were scattered and the spin-dependent intensities were measured. Comparative calculations were carried out by means of a relativistic LEED program. The structure determination of (√3 × √3)R30°-Xe/Pd(111) yields a layer distance of 3.5 ± 0.1 A ̊ , the Xe atoms being adsorbed in hollow sites. In the dilute phase of Xe/Pd(111) the adsorbed Xe atoms occupy on-top sites with a Xe-Pd distance of 4.0 ± 0.1 A ̊ without two-dimensional periodicity.

On surface amorphization and observation of surface magnetization in a semi-infinite ferromagnet

Some relationships between surface amorphization and magnetization at or near a surface are clarified by using a semi-infinite simple cubic spin-1/2 Ising ferromagnet with a free surface. Depending on the measuring depth in spin-polarized LEED or Mossbauer spectroscopy, it is discussed how the magnetization changes for the two cases where the surface is coupled ferromagnetically or antiferromagnetically to the bulk.

Xe-adlayers on Pt(111) and Pd(111): structure investigation by spin-polarized LEED

(√3 × √3)R30 ° Xe-layers on Pt(111) and Pd(111) are studied by spin-polarized LEED. In the experiment spin-polarized electrons from a GaAs photoemission source were scattered and the spin-dependent intensities are measured in different diffracted beams. Corresponding calculations were performed using a new relativistic LEED code. Measurements and calculations agree reasonably. They show strong contributions from multiple scattering between substrate and adlayer, and therefore spin-polarized LEED reveals strong sensitivity to structural parameters.

Xe-adlayers on Pt(111) and Pd(111): structure investigation by spin-polarized LEED

Xe-adlayers on Pt(111) and Pd(111): structure investigation by spin-polarized LEED

Spin-polarized LEED from Xe [sbnd]Pt(111)

(√3 × √3)-R30° Xe layers on Pt(111) were studied by spin-polarized LEED. Spin-polarized photoelectrons from a GaAs source were diffracted and the spin-dependent intensities of the adsorbate-induced beams were measured. Different adsorbate-induced beams not equivalent by symmetry in the system Xe-Pt(111) but equivalent in an isolated Xe layer show identical spin-dependent scattering asymmetries indicating a diminishing interlayer scattering and thus a diminishing influence of the substrate. Thus the adsorbate-induced beams are not suitable for structure determination. Spin-dependent scattering asymmetries measured in spin-polarized LEED of adsorbed Xe show a structure similar to one in asymmetry profiles of free Xe known in the literature.

Spin-polarized LEED investigation of the magnetized Ni(111) surface

Experimentally-determined exchange and spin-orbit induced scattering asymmetries A ex and A so for spin-polarized electrons diffracted from a magnetized Ni(111) surface are reported together with the results of fully relativistic dynamical LEED calculations. Comparison between theory and experiment shows generally good agreement and suggests that use of a model scattering potential incorporating an energy-dependent exchange correlation and localized absorption inside the muffin-tin spheres is to be preferred. Such comparisons also indicate that the surface is ferromagnetic with a top-layer magnetization comparable to that of the bulk.

Laser annealing of Ni(001)

The use of laser annealing in the preparation of a clean, well-ordered Ni(001) surface has been investigated. The surface was cleaned by argon ion bombardment and subsequently irradiated with the fundamental output of a high power, Q-switched ruby laser. The laser treated surface was characterized by use of Auger electron spectroscopy and both conventional and spin-polarized LEED, and the data compared to that from a surface prepared by thermal annealing. Laser irradiation of a sputtered surface at energy densities of ∼0.8 J cm−2 leads to complete removal of residual argon without segregation of carbon or other contaminants at the surface. However, irradiation at an elevated temperature ∼200 °C is required to obtain a well-ordered surface. At elevated temperatures, laser annealing provides a surface with cleanness and surface order comparable to that obtained by conventional thermal annealing.

Electron spin polarization esp at surfaces of ferromagnetic metals

Fundamental information on surface magnetic order (SMO) of ferromagnetic metals can be obtained from electron-capture, photoemission, fieldemission, spin-dependent tunneling and spin-polarized LEED experiments. The different techniques, new experimental advances and developments are discussed with particular emphasis given to electron-capture spectroscopy. This review will focus on new experimental and theoretical results (long-range and “local” SMO of ferro- and antiferromagnetic metals, surface states, SMO of thin films, new magnetic surface phases, magnetic surface reconstruction, chemisorption) obtained in the years past which have brought outstanding progress towards a deeper comprehension of the physics of ferromagnetism and towards the unravelling of the physical processes inherently involved in the various methods for spin spectroscopy. Recent data on the SMO received from experiments performed at surfaces of single crystals of 3d-TM and 4f-RE metals reveal new scientific insights and perspectives for the theoretical analysis of experimental results within the framework of the currently refined knowledge about ferromagnetism.

Surface barrier determination using spin-polarized LEED: W(001)

Spin-polarized LEED intensities have been calculated for the W(001) surface for a variety of surface barriers and compared with both spin-polarized measurements (15° ≤ angle of incidence Θ≤45°) and high resolution unpolarized data ( Θ=48°). Observed features, in particular the striking differences between spin-up and spin-down intensities, are reproduced satisfactorily by a barrier with an image plane 3.3 bohr from the outermost atomic layer and with a value of 70% of the bulk inner potential at that layer.

Symmetry properties of spin-polarized leed

The transformational properties of the polarizing power P and the analyzing power S of a polarized LEED beam under time reversal, rotations and reflections are derived. A general relationship between S and P is given, and special cases of equality are noted.

Spin-polarized LEED from low-index surfaces of platinum and gold

A relativistic theory of LEED has been applied, in the energy range from 0 to 200 eV, to (111) and (001) faces of Pt and Au. The calculated intensity versus energy profiles are in good agreement with experimental data, which, in particular, provides support for interpreting the observed surfaces as unreconstructed. As a consequence of strong spin-orbit coupling, large spin-polarization peaks are found, partly in conjunction with intensity maxima. As a rough guide to diffraction conditions, at which both polarization and intensity are sizeable, a simple kinematic model might be of some use.