Polarized Light Emission after Grazing Ion-Surface Scattering Due to Capture of Spin-Polarized Electrons

Winter, H.; Hagedorn, H.; Zimny, R.; Nienhaus, Hermann; Kirschner, J.

doi:10.1103/physrevlett.62.296

Cited by 66 publications

(20 citation statements)

References 20 publications

(17 reference statements)

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“…Ultimate surface sensitivity (magnetic probing depth λ = 0 ML) is achieved by spin-polarized electron capture [17,18]. 25 keV He + -ions are grazingly scattered (incidence angle to the surface plane 1 − 2…”

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confidence: 99%

Layer-dependent magnetization at the surface of a band ferromagnet

Pfandzelter

Potthoff

2001

Phys. Rev. B

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The temperature-dependence of the magnetization near the surface of a band-ferromagnet is measured with monolayer resolution. The simultaneous application of novel highly surface-sensitive techniques enables one to deduce the layer-dependent magnetization curves at a Fe(100) surface. Analysis of data is based on a simple mean-field approach. Implications for modern theories of itinerant-electron ferromagnetism are discussed.A ferromagnetic material is characterized by a spontaneous magnetization m which decreases with increasing temperature T until the paramagnetic state with m = 0 is reached at the Curie point T c . For very low temperatures the form of the magnetization curve m(T ) is governed by spin-wave excitations according to Bloch's law. For temperatures very close to T c critical fluctuations result in a power-law dependence m(T ) ∝ (T c − T ) β with a critical exponent β. In the wide range of intermediate temperatures the form of m(T ) depends on the specific system. In case of a band-ferromagnetic material, such as Fe as a prototype, the detailed form of m(T ) in this intermediate regime must be explained from the underlying electronic structure [1,2].Density-functional theory within the local-spin-density approximation is known to give a quantitatively accurate description of several ground-state properties [3]. For finite temperatures, however, there is no satisfying implementation available. A microscopic theory must account for the existence of local magnetic moments above T c in particular [4]. This requires to deal with correlations among itinerant valence electrons as, for example, within the framework of an orbitally degenerate Hubbard-type model with realistic parameters [5]. The long history of itinerant-electron ferromagnetism shows that this is a demanding task [2]. On the other hand, comparatively simple mean-field approaches based on spin models are known to provide a successful phenomenological description in many cases (see e. g. Ref.[6]). Remarkably, while the Weiss mean-field theory fails to reproduce the known T → 0 and T → T c limits and substantially overestimates T c , the form of the Fe magnetization curve m(T ) at intermediate reduced temperatures T /T c is reasonably well described: For spin-quantum number S = 1/2 there are deviations from the measured bulk magnetization curve of Fe within a few per cent only [7,8].At the surface of a band-ferromagnet the magnetization may be different for different layers α parallel to the surface because of the reduced translational symmetry. Hence, a key quantity that characterizes the surface magnetic structure is the layer-dependent magnetization curve m α (T ). Within the framework of classical spin models, the lowered surface coordination number implies that certain exchange interactions are missing. This directly leads to a reduced magnetic stability at the surface [9]: The top-layer (α = 1) magnetization is substantially reduced as compared with the bulk. However, significant deviations from the bulk magnetization curve are confined t...

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confidence: 99%

Layer-dependent magnetization at the surface of a band ferromagnet

Pfandzelter

Potthoff

2001

Phys. Rev. B

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“…Kupfer et al [2] suggested to enhance the atomic anisotropy in grazing surface collisions by capture of polarized electrons and analyzed theoretically the emission of polarized light. First experimental evidence for this concept has been reported by Winter et al [4] for the excitation of fast atoms in grazing collisions with a magnetized Fe(ll0)-surface. A detailed description of the experimental procedures and the analysis of data can be found below.…”

Section: Pl(t):#pl(o) Ps(t)e~ps(o) and Pi(t)o Since It Ismentioning

confidence: 92%

“…This technique has been suggested by Kupfer et al [2] and is based on the concepts of "Electron Capture Spectroscopy" (ECS) introduced to the field of ion-surface scattering by Rau and Sizmann [3]. In two recent communications we reported briefly on first results obtained by this technique [4]. Main purpose…”

Section: Introductionmentioning

confidence: 96%

Capture of polarized electrons into excited terms of fast atoms during grazing surface collisions

Winter

1992

Z Phys D - Atoms, Molecules and Clusters

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Atoms, Molecules zo,,oo.r,, and ClustersAbstract. Fast ions are scattered from magnetized surfaces under grazing angles of incidence. During the interaction with the surface charge exchange is effective and results in a population of stable and excited atomic terms. This capture of electrons is characterized by anisotropic distributions of atomic orbital angular momenta and in addition -for magnetized targets -by anisotropic distributions of electronic spins. We will discuss in some detail, how these anisotropic distributions can be studied via the analysis of the state of polarization of the fluorescent light, emitted in electronic transitions from excited terms of free atoms after the impact with the surface. We show that a defined variation of the magnetization of the target affects the polarization of the emitted light in a characteristic way, which allows to deduce the electronic spin polarization of the atoms. The method implies some perspectives with respect to the study of magnetic properties of the vacuum-solid interface well above the topmost layer of surface atoms. 34.50.Fa of this paper is to outline in some detail the concepts and experimental procedures of our studies. PACS:We will discuss first the capture of polarized electrons into atomic terms during ion-surface collisions and its effect on the anisotropic distribution of angular momenta in free atoms. This anisotropy is investigated by the analysis of the (polarized) light emitted in transitions from excited atomic terms after the interaction with the surface. Based on a theoretical description of the coupling of anisotropic ensembles of angular momenta and spins, we obtain the atomic and electronic spin polarization from an analysis of the light polarization for defined settings of the magnetization of the target. Then we describe the application of this procedure to the capture of polarized electrons into a number of different excited terms of atoms/ions with different orbital angular momenta and multiplicities. After a presentation and discussion of our experimental results we will outline concepts of charge exchange in grazing surface collisions and its relevance and perspectives with respect to the capture of polarized electrons.

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“…Polarization measurements have not been published for this system as yet, but for Cu(111) at intermediate impact energies (100-300 keV) [14], for Ni(lll) at low energies (3-29 keV) [15] and for Fe(ll0) at 3 to 350 keV [16]. The quantitative understanding of Na* (3p)-formation near AI(111) may also be considered as a prerequisite for any understanding of the chargetransfer dynamics in Na*(3p)-population in front of magnetized surfaces, which may serve as a probe to investigate surface magnetism [16][17][18]. Level widths and shifts are already available for the lowest excited states of alkali atoms near jellium surfaces [8]+ Here we will report on calculations ofNa* (3p)-formation under grazing angle collisions with an Al-like jellium surface in dependence on the projectile velocity.…”

Section: Introductionmentioning

confidence: 99%

Na*(3p)-Formation under grazing scattering of Na+-ions at an Al(111) surface

Zimny

Borisov

1994

Z Phys D - Atoms, Molecules and Clusters

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Abstract. Excited Na* (3 p)-atoms are observed in grazing surface-collision experiments with Na+-beams. Such atoms can be formed beyond a certain threshold velocity via resonant electron transfer between atomic and metallic conduction band levels due to motion of the atom relative to the surface of the metal ("kinematic resonance"). This mechanism is studied here theoretically employing two different techniques: the nonperturbative "Coupled Angular Mode" (CAM) method and the approximate "Transfer Hamiltonian" (TH) method. The calculated Na*(3p)-populations agree well with recent experimental results. Moreover, the complete density matrix of the Na* (3 p)-subspace has been computed with the TH-method for ion-energies between 10 and 300 keV.

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Polarized Light Emission after Grazing Ion-Surface Scattering Due to Capture of Spin-Polarized Electrons

Cited by 66 publications

References 20 publications

Layer-dependent magnetization at the surface of a band ferromagnet

Layer-dependent magnetization at the surface of a band ferromagnet

Capture of polarized electrons into excited terms of fast atoms during grazing surface collisions

Na*(3p)-Formation under grazing scattering of Na+-ions at an Al(111) surface

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