Browsing by Author "Rau, C."

Now showing 1 - 15 of 15
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    Angle- and energy-resolved, spin-polarized electron emission spectroscopy to study surface magnetic and electronic properties
    (American Physical Society, 1990) Rau, C.; Waters, K.; Chen, N.
    We report on a new technique, spin-polarized electron emission spectroscopy. Using grazing-angle, surface scattering of H+ and He+ ions at Ni(110), we find that the angle-resolved energy distribution of emitted spin-polarized electrons is significantly different from that of electron-induced secondary (cascade) electrons and exhibits a series of characteristic ‘‘peaks’’ (including element-specific Auger electrons). We obtain characteristic, spin-dependent information on the surface electronic structure of Ni(110) and on atom-surface charge-transfer processes.
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    Electron-Spin Polarization at Single-Crystalline Cr and Ni Surfaces Determined with Electron-Capture Spectroscopy
    (American Physical Society, 1981) Rau, C.; Eichner, S.
    The spin polarization P of electrons at Cr and Ni surfaces is measured with electron-capture spectroscopy. With use of one-electron capture at magnetized Cr(100)-c(2×2) surfaces at 293 K (TN=310 K), P values up to -18% are found revealing ferromagnetic order at this surface. Utilizing two-electron capture at demagnetized Ni surfaces we find at 293 K (TC=631 K) |P|=94% for Ni(110), |P|=72% for Ni(100), |P|=47% for Ni(111), and |P|=14% for Ni(120). There is evidence that "local" ferromagnetic order at Ni surfaces exists even at 2TC.
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    Evidence for 4d Ferromagnetism in 2D Systems: Ru Monolayers on C(0001) Substrates
    (American Physical Society, 1995) Pfandzelter, R.; Steierl, G.; Rau, C.; Rice Quantum Institute
    The first observation of 4d ferromagnetism in two-dimensional systems is reported. Using Auger electron spectroscopy, we find that the initial growth of Ru on a C(0001) substrate is lateral until a homogeneous monolayer film is formed. The magnetic properties of the films are studied using spin polarized secondary electron spectroscopy. For one monolayer Ru on C(0001), below a surface Curie temperature of approximately 250 K, nonzero in-plane spin polarization is observed and found to saturate in an applied field of a few tenths of an Oe. The results are discussed in the light of theoretical predictions.
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    Evidence for ferromagnetic order at gadolinium surfaces above the bulk Curie temperature
    (American Physical Society, 1986) Rau, C.; Eichner, S.
    The electron-spin polarization P at the topmost layer of atomically clean, magnetized gadolinium (Gd) surfaces is measured by using electron capture spectroscopy. P varies almost linearly with temperature between 160 K (P=-42%) and 315 K (P=0). It is found that the surface Curie temperature TCs is far above—lying near 310 K—the bulk Curie temperature TCb=292.5 K, indicating uniaxial anisotropic magnetic exchange interactions at the topmost surface layer of Gd.
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    Ferromagnetic Order at (100) p(1×1) Surfaces of Bulk Paramagnetic Vanadium
    (American Physical Society, 1986) Rau, C.; Liu, C.; Schmalzbauer, A.; Xing, G.
    Electron-capture spectroscopy has been used to investigate magnetic order at the topmost atomic layer of atomically clean and flat (100) surfaces of bulk paramagnetic vanadium. From low-energy electron diffraction measurements, we find a p(1×1) surface structure. At 300 K, the long-ranged electron-spin polarization amounts to ∼34%, clearly demonstrating the existence of ferromagnetic order at the V(100) p(1×1) surface. With increasing temperature, the electron-spin polarization decreases almost linearly and disappears at a surface Curie temperature TCs≈540 K.
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    Ferromagnetic order at surfaces of ultrathin epitaxial fcc γ-Fe(111)p(11) films on Cu(111)
    (American Physical Society, 1986) Rau, C.; Schneider, C.; Xing, G.; Jamison, K.
    Electron-capture spectroscopy has been used to investigate long-ranged and short-ranged two-dimensional magnetic order at free (uncoated) surfaces of homogeneous (island-free), ultrathin fcc γ-Fe(111)(1×1) films pseudomorphically deposited on Cu(111) substrate crystals. At 298 K, the electron-spin polarization at the surface of a four-monolayer thin fcc Fe film amounts to +16%, directly revealing the existence of long-ranged ferromagnetic order. There is evidence that short-ranged ferromagnetic order still exists at 400 K at free surfaces of two and one-monolayer thin fcc Fe films.
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    Influence of magnetism on second harmonic generation
    (American Physical Society, 1993) Reif, J.; Rau, C.; Matthias, E.
    Optical second harmonic generation (SHG) in 75° reflection was studied on longitudinally magnetized PtMnSb(111) and magnetic circular dichroism was observed with SHG. For circularly polarized incident light of 532 nm it amounts to (7±1)%. For linearly polarized incident radiation this leads to a nonlinear magneto-optical Kerr rotation of (14±2)°. The strong symmetry-breaking effect of the magnetization is demonstrated by a 90° turn of the SH polarization ellipse with regard to the linear polarization of the fundamental light.
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    Magnetic domain structures of focused ion beam-patterned cobalt films using scanning ion microscopy with polarization analysis
    (AIP Publishing LLC, 2004) Li, J.; Rau, C.; Rice Quantum Institute; Center for Nanoscience and Technology
    Studies of magnetic domain distributions in patterned magnetic materials are of pivotal importance in the areas of ultrahigh density magnetic recording, MRAM design, and miniaturized magnetic sensor arrays. Scanning ion microscopy with polarizationanalysis (SIMPA) is used to perform in situ topographic and magnetic domain imaging and focused ion beam(FIB) patterning. For FIB-patterned 30 nm thick Co films, it is found that rectangular Co bars of sizes between 10–30 μm exhibit S type, whereas circular shaped magnetic elements show C type micromagnetic magnetization patterns. It is shown that SIMPA provides a simple way to directly identify different micromagnetic domain patterns.
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    Probing the Surface-Vacuum Interface with Spin-Sensitive Metastable Atom Deexcitation, Electron Capture and Electron Emission Spectroscopies
    (Cambridge University Press, 1993) Walters, G.K.; Rau, C.; Rice Quantum Institute
    Spin-Polarized Metastable Atom Deexcitation (SPMDS) and Electron Capture (ECS) Spectroscopies probe the exponential tails of electronic wavefunctions extending from the surface into the vacuum, and are consequently extremely sensitive to the surface-vacuum interface. The use of SPMDS to probe the near-surface vacuum magnetization of Ni (l 10) and Fe (l 10) and the dramatic changes that result upon exposure to ambient gases is discussed, as is the use of ECS and Spin-Polarized Electron EMission Spectroscopy (SPEES) to determine the ferromagnetic and critical behavior of surfaces and ultra-thin epitaxial systems.
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    Scanning-Ion Microscopy with Polarization Analysis (Simpa)
    (Cambridge University Press, 1993) Zheng, N.J.; Rau, C.; Rice Quantum Institute
    We have developed a novel, high-resolution magnetic imaging technique, scanning-ion microscopy with polarization analysis (SIMP A). In SIMP A, a highly-focused, scanning Ga+ ion beam is used to excite spin-polarized electrons at surfaces of ferromagnetic materials. By measuring the intensity and the spin polarization of the emitted electrons using a newly developed, compact Mott polarimeter, topographic and magnetic images of magnetic structures are obtained. We report on first SIMP A studies on single crystalline Fe samples.
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    Strong Influence of Tb Concentration on Domain Structure and Kerr Effect of TbxFe1−x Thin Films
    (Cambridge University Press, 1993) Florescu, V.; Rau, C.; Zheng, N.J.; Rice Quantum Institute
    Amorphous TbFe films with perpendicular magnetic anisotropy are attracting wide attention as promising candidates for erasable high - density Magneto - optical recording and thermomagnetic printing. TbxFe1−x thin films with 0 ≤ × ≤ 0.37 are deposited on glass substrates using r.f. sputtering. The Magnetic remanent domain structures are studied at room temperature using the longitudinal and polar Kerr effect. Samples with 0 ≤ × ≤ 0.23 exhibit magnetic in-plane anisotropy, while samples with 0.26 ≤ × ≤ 0.37 possess uniaxial anisotropy with easy axis perpendicular to the film plane. The remanent domain structures depend strongly on Tb content. High remanence and high coercivity are found for samples with 0.27 ≤ × ≤ 0.34 which is confirmed by additional vibrating sample Magnetometer (VSM) Measurements.
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    Surface magnetization of Gd at the bulk Curie temperature
    (American Physical Society, 1987) Rau, C.; Robert, M.
    Electron-capture spectroscopy is used to study the long-ranged surface ferromagnetic order of Gd in the neighborhood of the bulk Curie temperature TCbulk at which, unlike bulk ferromagnetic order, it does not vanish. The surface magnetization, together with its first temperature derivative, is found to be a continuous function of temperature at TCbulk and, as temperature is varied, the surface magnetization is found to depart linearly from the nonzero value it assumes at TCbulk, with critical exponents x+=1.00±0.03 (T>TCbulk) and x−=1.00 ±0.01 (T
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    Three-Dimensional, Spin-Resolved Structure of Magnetic Vortex and Antivortex States in Patterned Co Films Using Scanning Ion Microscopy with Polarization Analysis
    (American Physical Society, 2006) Li, J.; Rau, C.; Rice Quantum Institute; Center for Nanoscience and Technology
    Scanning ion microscopy with polarization analysis is utilized for three-dimensional spin mapping of the surface magnetization (SM) of circular Co dots created inﾠsitu by focused ion beam etching of 30ﾠnm thin Co/Si(100) films. From 3D scanning ion microscopy with polarization analysis spin maps, direct evidence is found for the existence of vortex-antivortex states with in-plane circular or hyperbolic SM components and a wide core with perpendicular SM components which oscillate in the outer region and become zero.
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    X-ray laser implementation by means of a strong source of high-spin metastable atoms
    (American Physical Society, 1983) Helman, J.S.; Rau, C.; Bunge, C.F.
    High-spin metastable atomic beams of high density and extremely small divergence can be produced by electron capture during grazing-angle scattering of ion beams at ferromagnetic surfaces. This can be used to generate a long-lived reservoir of Li 1s2s2p P5204 with enough density of metastables so that after laser-induced transfer to Li 1s2p2P2 strong lasing at 207 Å should occur. This novel technique can also be used to produce a variety of other metastables known as potential candidates for lasing at shorter wavelengths.