Observation of a high spin polarization of secondary electrons from single crystal Fe and Co

The spin polarization of secondary electrons with nearly zero kinetic energy from Fe (100) and Co (10$\text{1}$0), excited with photons of energy between 20 and 60 eV, was found to be 45%±5% for Fe and 35%±5% for Co. This value is higher than the average valence band spin polarization P_b=n_b/n=2.2/8=27% and 1.7/9=19% for Fe and Co, respectively. With increasing kinetic energy, the spin polarization of the secondaries decreases to the value of P_b within the first 5 eV, remaining constant (within statistical error) at higher kinetic energies. As a spin dependent scattering process we propose excitations within the d-bands, which can be shown to be asymmetric with respect to the electron spin. The high net spin polarization of the slowest emitted electrons is obtained by filtering out monitory-spin electrons at the vacuum barrier.     

Spinpolarisation von Feldemissionselektronen aus einkristallinem Wolfram

Field-emitted electrons from tungsten tips extracted in magnetic fields of 3–25 kG at 80 K show spin polarization. The observed polarization is always found to be parallel to the external magnetic field for the polycrystalline and oriented tips (〈100〉, 〈110〉 and 〈111〉) investigated. The maximum values of polarization obtained with these monocrystalline emitters range betweenP _max=11–13 percent.     

Theoretical study for magnetic effect in dissociative adsorption of oxygen to a platinum monolayer on Ni(110) surface

We investigate oxygen dissociative adsorption to a platinum monolayer on Ni(110) surface (Pt/Ni(110)) by density functional theory. We have shown that the activation barrier on Pt/Ni(110) is lower than that on a clean Pt(001) surface. This may be due to the effect of magnetization of Pt surface. The reason of decrease of activation barrier can be attributed to the flow of electrons from oxygen to platinum surface because the d orbitals have spin polarization at the Fermi level where the down spin d orbitals are unoccupied.     

Untersuchung der Polarisationsebene von Photonen nach Compton-Streuung an polarisierten Elektronen

Two polarization phenomena in Compton scattering by polarized electrons were investigated. In the first experiment, the rotation of the polarization plane of photons passing through magnetized iron and gadolinium was measured. This effect arises from a spin dependence of the Compton forward scattering amplitude. For 228 and 333 keV photons and iron absorbers, the observed rotation angles areφ ₀=(3.90±0.57) ×10^?3 rad · cm^?2 and (4.75±0.58)×10^?3 rad · cm^?2, respectively. Secondly, the orientation of the photon polarization plane after scattering of unpolarized photons by polarized electrons was measured. This experiment tests time reversal invariance in quantum electrodynamics. No dependence of the polarization plane on the direction of the electron spin was found within 2×10^?3.     

Transmission of electrons through ferromagnetic material and applications to detection of electron spin polarization

The salient features of the total low energy inelastic electron scattering cross section in transition metals are described by a constant term σ₀ plus a term σ_d that is proportional to the number of unoccupied d-orbitals. This simple model predicts that low energy electrons transmitted through a ferromagnetic ultrathin film acquire a transport spin polarization a(χ). Using the ratio σ₀/σ_d as the only adjustable parameter, the model predicts the enhancement of the spin polarization of the low energy cascade electrons as well as a(χ) in reasonable agreement with the existing observations on Fe, Co and Ni. A detector for electron spin polarization P based on the spin dependent transmission of electrons through ferromagnetic material is proposed which should be superior to existing P-detectors by 1–2 orders of magnitude.     

Absolute coverage measurements of deuterium on Ni (110)

The absolute coverage of deuterium adsorbed on Ni(110) at temperatures below 170 K to the formation of a (1 × 2) LEED pattern has been determined by nuclear microanalysis (NMA). The result, θ_D = 0.96 ± 0.08, is consistent with a saturation coverage of one full monolayer. Heating the crystal above ～ 190 K is shown to result in a gradual loss of deuterium from the system, accompanied by streaking of the LEED pattern, with complete desorption above ～ 340 K. The low-temperature (2 × 1)-D phase was found to correspond to θ_D = 0.64 ± 0.05 monolayers. The results are expected to be valid also for the equivalent phases obtained by hydrogen adsorption.     

A study of inclusive Λ polarization from hydrogen and other targets at 28 GeV

We report measurements of inclusive Λ polarization, produced by unpolarized protons incident at several momenta (20, 24, and 28.5 GeV/c) onto hydrogen, deuterium, and beryllium targets. A large polarization from hydrogen, P = ?0.34 ± 0.06 at pP_T = 1.2 GeV/c, establishes the fact that inclusive Λ polarization arises from p-p collisions.     

Effects of adsorbates on electron spin polarization in low energy electron diffraction from tungsten (001): II. Ordered CO overlayer

Electron spin polarization and intensity profiles have been measured in low electron diffraction (LEED) for the (00) beam at θ = 13° and ø = 0° from a W(001) surface exposed to CO and annealed to obtain an ordered c(2 × 2) CO overlayer. The annealed surface with additional CO adsorbed was also studied. The polarization was found to be sensitive to the surface condition and the very distinct P?V profile corresponding to the c(2 × 2) overlayer is believed to be a very sensitive indicator of CO in the β₃ phase. The properties of the annealed surface exposed to further CO suggest the use of this surface as a low energy electron spin polarization analyzer.     

Polarization of prompt muons produced at large transverse momenta

We measured the longitudinal and transverse polarization of prompt muons produced at ～2 GeV/c transverse momentum by the interaction of 28.5 GeV protons on tungsten. Both components of the polarization were found to be consistent with zero: P_L = ?0.15 ± 0.18 and P_T = 0.05 ± 0.05.     

Muon-spin-rotation study of muon polarization losses in plastic scintillators and quartz

Muon polarization losses in plastic scintillators of two types and in fused quartz have been studied by the μSR method. The muon and muonium spin precession spectra have been measured on the μSR setup placed at the output of the muon channel of the Gatchina synchrocyclotron. It has been shown that a significant fraction of stopped muons participate in the formation of the muonium. As a result, these muons lose their polarization completely. The magnitude of muon depolarization depends considerably on the type of plastic. It has been found that the muon spin precession frequency in fused quartz in an external magnetic field (F _{Q, μ} = 0.116 ± 0.002 MHz) is shifted with respect to that in plastic scintillators (F _{1, μ} = 0.101 ± 0.005 MHz and F _{2, μ} = 0.101 ± 0.002 MHz).     

Elektronenpolarisation im Energiebereich unterhalb 50 eV durch Streuung an freien Hg-Atomen

The angular dependence of spin polarizationP(Θ) of electrons elastically scattered by a beam of mercury atoms is measured in a double scattering experiment for electron energies of 45±1 eV; 23±1 eV; 7±1 eV; and 3,5±1 eV. Maximum degree of polarization obtained isP(100°)=0,39±0,07; electron energy 7±1 eV; electron current 10^?12–10^?11 A.     

Dual path surface reconstruction in the H/Ni (110) system

Reconstruction of a Ni (110) surface under the influence of adsorbed hydrogen atoms can proceed in two different ways: Below 180 K a 2×1 lattice-gas structure with θ_H = 1.0 transforms cooperatively into a two-dimensional 1×2 structure by additional uptake of hydrogen up to θ_H = 1.5. At higher temperatures, activated local transformation into a more stable one-dimensional structure starts already at low coverages.     

Übertragung von Polarisation bei sensibilisierenden Stößen angeregter Natriumatome

The transfer of magnetic polarization between the levels² P _1/2 and² P _3/2 in sensitizing collisions of excited sodium atoms and noble-gas atoms has been studied. Deviating from a previous study on this topic the nuclear spin was now decoupled by means of a strong magnetic field. As a result moreD ₂σ^?-quanta could be detected in the sensitized fluorescence following an excitation withD ₁σ⁺-light. From the measurement of the fluorescence intensitiesI _D1σ± andI _D2σ±, cross-sections peculiar to polarization transfer could be derived. In the case of He and Ne these cross-sections together with the cross-sections of normal sensitizing collisions could be traced back to Grawert's parametera ₁ anda ₂ hence confirming the assumption of the spin being “at rest” during the collision.     

Angular momentum dissipation in16O +58Ni collisions investigated by observation of light particles andγ rays

A systematic study of angular momentum dissipation in deep-inelastic heavy ion collisions is carried out by combining two experimental methods: the angular correlation ofα particles and protons in coincidence with deeply inelastic light fragments; and the first two moments of theγ-ray multiplicity. The unified analysis of these data, using a quantum mechanical treatment of the particle anisotropies and statistical decay calculations, yields most probable fragment spinsI ₀=10.8±1.1? and 13.4±1.1? for⁵⁸Ni and⁶²Zn, respectively, close to the sticking limit. For the width of the vector spin distribution assumed in our analysis to be equal in all three directions we obtainσ=3.9±1.3 ? and 2.9±1.8? for⁵⁸Ni and⁶²Zn, respectively. These values correspond to most probable alignment parameters 〈P _zz〉=0.66±0.19 and 0.82±0.17 for⁵⁸Ni and⁶²Zn, respectively. As only very few partial waves of this light system undergo deep-inelastic scattering,σ directly relates to spin fluctuations, and is compared to asymptotic values from transport theories.     

Microwave cyclotron resonance of hot electrons in p-type GaSb

A microwave photocreated cyclotron resonance signal is observed in p-type GaSb in the temperature range 1–30 K. Circular polarization and other measurements identify the carriers as electrons in the (000) conduction band. The problem of a surface effect on the measured peak position, reported for the first time is avoided by bulk carrier creation. An exponential loss of signal intensity at 27 K is explained by the theory of background plasma effects. The measured ωτ of 1·5–4 yields an electron collision time of τ ～ 10^?11 sec. The scattering mechanism at liquid helium temperatures is identified as being partly due to neutral defect acceptor scattering of hot electrons, with an unidentified residual scattering process. The electron polaron effective mass is measured to be (m *(polaron)/m₀) = 0·0412 ± 0·0012 for hot electrons with an average energy of ～ 14 MeV and is isotropic within 1 per cent. When corrections for conduction-band non-parabolicity and hot polaron effects are applied, the band-edge free electron mass is calculated to be (m₀*(free)/m₀) = 0·0396 ± 0·0021 (±5·2 per cent).     

Determination of the Spin–Spin Coupling Constant in Hydrogen Deuteride HD and Estimates of the Manifestation of Axion-Like Particles

An experimental value of the spin–spin coupling constant in deuterated molecular hydrogen HD has been obtained, J _pd = (43.112 ± 0.005) Hz (300 K), while investigating two gaseous samples at pressures of 95 and 155 atm. The experimental result does not coincide with Jpd = (43.31 ± 0.05) Hz that was calculated theoretically by Helkager et al. The observed discrepancy ΔJ _pd ≈ (0.20 ± 0.05 Hz) may point to a manifestation of the involvement of light pseudo-scalar (axion-like) bosons with a mass m _a ≈ 1 keV/c² in the spin–spin coupling of the HD proton and deuteron.     

The pion radius

The pion radius has been measured by direct scattering of 50 GeV negative pions from stationary electrons in a hydrogen target. We find the square of the radius to be 〈r_π²〉 = (0.61 ± 0.15)fm².     

Electron paramagnetic resonance of Fe3+ in orthorhombic KNbO3

EPR spectra of KNbO₃:Fe single crystals are obtained in the - 10–110°C temperature range. The angular dependence of resonant lines is well reproduced by spin Hamiltonian parameters relevant to a Fe³⁺ impurity ion substituted to Nb ion in KNbO₃ crystal. The temperature behaviour of resonant lines is explained by a quadratic dependence of axial parameter D vs polarization P_s of the form D = βP²_s in the orthorhombic phase.     

Spin polarization for electrons tunneling from MnxSb1−x

The spin polarization of electrons tunneling from Mn_xSb_1?x was measured over the full Mn concentration range 0 ? x ? 1. The polarization is positive and qualitatively similar to the magnetization per Mn atom of bulk material; for MnSb (x = 0.5) it is + 25%.     

Direct pair production by positive and negative electrons in a hydrogen bubble chamber

The production of electron pairs by negative and positive electrons in the energy region 0.65 – 5.8 GeV has been investigated in the DESY 81-cm hydrogen bubble chamber. The effective cross section σ = 0.62 ± 0.04 mb averaged over the energy spectrum of incident electrons is found to be in good agreement with the predictions of quantum electrodynamics. The energy distribution of created pairs as well as the dependence of the total cross section on energy are best represented by the expression of Murota, Ueda and Tanaka with the constant c = 0.66 ± _0.17^0.24 and by Bhabhá's formula with the constants c₁ = 1 and c₂ = 2.8 ± _0.7^0.9. The contribution of the interference term between space-like and time-like Feynman diagrams to the cross section is estimated to be less than about 10% and to fall off with an increase of the incident energy.