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  • 1
    Digitale Medien
    Digitale Medien
    Spin-polarized photoemission study of epitaxial Gd(0001) films on W(110) : 37th Annual conference on magnetism and magnetic materials (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 6769-6771 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Surface magnetic properties of epitaxial Gd(0001) films grown on W(110) were studied with spin-polarized resonant 4f photoemission. Films grown at room temperature and subsequently annealed to 550 °C show 66% polarization at 150 K, whereas films grown at 400 °C show only 46% polarization. Both types of films exhibit surface enhanced magnetic order, with the highest observed surface critical temperature exceeding the bulk value by as much as 60 K. For the first time, a rich variety of novel surface magnetic phenomena, i.e., sizeable perpendicular polarization component and unusual temperature hysteresis in the spin polarization, are observed, demonstrating that surface magnetic reconstruction is present in Gd(0001) films.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.352480
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  • 2
    Digitale Medien
    Digitale Medien
    Magnetic dichroism in core-level photoemission from fcc Fe/Cu(100) films : 37th Annual conference on magnetism and magnetic materials (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 5936-5938 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Circularly polarized x rays from a synchrotron light source were used in photoemission from thin fcc Fe films on Cu(100). The measured exchange splitting for the 3s and 2p levels in these films is reduced from that measured in bulk bcc Fe. For both the 2p3/2 and the 2p1/2 levels the splittings are about half that of bulk bcc Fe. This trend is in line with measurements of the 3s exchange splitting from fcc Fe compared to bcc Fe as well. A 0.25 eV exchange splitting is observed in the 3p core level.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.353527
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  • 3
    Digitale Medien
    Digitale Medien
    Magnetic x-ray dichroism in 2p absorption spectra of Fe/Cu(001) : 37th Annual conference on magnetism and magnetic materials (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 6748-6750 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Large magnetic circular dichroism using circularly polarized synchrotron radiation has been observed at the L2,3 absorption edges of thin (1–12 monolayers) fcc Fe films grown on Cu(001). Dramatic changes in the 2p branching ratio are observed when the orientation of photon helicity and sample magnetization are varied from parallel to antiparallel. The temperature and film thickness dependence of the perpendicular anisotropy in these films could be monitored by variations in the 2p branching ratio. Finally, our results are described in a simple theoretical framework that allows a determination between the predicted low- and high-spin phases for fcc Fe. Our data suggest a high-spin phase with a moment of 2.0–2.5 μB/atom. Interestingly, thicker films with remanant magnetic moments in the film plane present smaller branching ratio variations consistent with either a reduced moment or with domain closure for these films. The surface sensitivity and elemental specificity of this technique make it particularly attractive for the study of surface and thin film magnetism.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.352524
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  • 4
    Digitale Medien
    Digitale Medien
    Magnetism of ultrathin films of Fe on Cu(100) : 35th annual conference on magnetism and magnetic materials (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 5209-5211 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Magnetism in ultrathin (1–10 ML) Fe films grown on Cu(100) has been studied by spin-polarized secondary electron emission spectroscopy. The variation of the magnetization with temperature and oxygen adsorption was investigated for various film thicknesses. The orientation of the magnetization for films between 5 and 6 ML thick switches reversibly between perpendicular (at low temperature) to in-plane (at high temperature). The switching transition temperature decreases with increasing film thickness, and is accompanied by a loss of long-range order over a range of 20–30 K. The transition is attributed to the temperature dependence of the perpendicular anisotropy. The effect of oxygen adsorption onto films with perpendicular remanence is to first suddenly turn the magnetization into the plane at a critical coverage, and then to kill the magnetization gradually with continued exposure. This indicates that the uniaxial surface anisotropy at the Fe-vacuum interface plays a major role in the magnetization of the film.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.348077
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  • 5
    Digitale Medien
    Digitale Medien
    Domain formation near the reorientation transition in perpendicularly magnetized, ultrathin Fe/Ni bilayer films (invited) (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 5054-5059 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Ultrathin films with perpendicular magnetization convert from a single domain state into a multidomain structure as the reorientation phase transition to an in-plane magnetization is approached. Reorientation transitions in magnetic ultrathin films result from the interplay of interfacial magnetic anisotropy, the dipolar interaction, and two-dimensional thermodynamics. These transitions can be driven by changing either the film thickness or temperature. Experimental and theoretical studies of this effect are briefly discussed in the context of the thickness–temperature phase diagram of the reorientation transition. We then describe magnetic susceptibility experiments on ultrathin Fe/Ni(111) bilayers. Our experiments indicate an exponential increase in domain density of a multidomain structure with temperature and identify the region of the thickness–temperature reorientation transition phase diagram where this condensation is most pronounced. The temperature dependence of the domain density agrees quantitatively with theoretical predictions. Films that are slightly too thin to exhibit the reorientation transition with temperature are a special case. They undergo a ferromagnetic-to-paramagnetic transition from the perpendicularly magnetized state and exhibit domain-like behavior many tens of Kelvin above estimates of the Curie temperature. This surprising observation is interpreted using the two-dimensional dipolar Ising model. © 1999 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.370089
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  • 6
    Digitale Medien
    Digitale Medien
    High confinement dissipative divertor operation on Alcator C-Mod : The 40th annual meeting of the division of plasma physics of the american physical society (1999)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 6 (1999), S. 1899-1906 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Alcator C-Mod [I. H. Hutchinson et al., Phys. Plasmas 1, 1511 (1994)] has operated a High-confinement-mode (H-mode) plasma together with a dissipative divertor and low core Zeff. The initially attached plasma is characterized by steady-state enhancement factor, HITER89P [P. N. Yushmanov et al., Nucl. Fusion 30, 1999 (1990)], of 1.9, central Zeff of 1.1, and a radiative fraction of ∼50%. Feedback control of a nitrogen gas puff is used to increase radiative losses in both the core/edge and divertor plasmas in almost equal amounts. Simultaneously, the core plasma maintains HITER89P of 1.6 and Zeff of 1.4 in this nearly 100% radiative state. The power and particle flux to the divertor plates have been reduced to very low levels while the core plasma is relatively unchanged by the dissipative nature of the divertor. © 1999 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.873447
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  • 7
    Digitale Medien
    Digitale Medien
    Volume recombination and opacity in Alcator C-Mod divertor plasmas : The 39th annual meeting of division of plasma physics of APS (1998)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 5 (1998), S. 1759-1766 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Volume recombination within the Alcator C-Mod [I. H. Hutchinson et al., Phys. Plasmas 1, 1511 (1994)] divertor plasma is measured and found to be a significant fraction of the total ion sink under detached divertor conditions. The recombination occurs in regions where Te∼1 eV and ne∼1021 m−3. Measurements of the spatial distribution of the recombination are presented. The determinations of the recombination rates are made by measuring the D0 Balmer spectrum and by using a collisional radiative model describing the level populations, ionization, and recombination of D0. The concept of "recombinations per Balmer series photon" is developed to simplify the determinations. Measurements of the opacity of Lyβ emission are presented. It is observed that up to 50% of the Lyβ emission is trapped, indicating that Lyα is strongly trapped in some cases. The effects of Lyα,β trapping on the "recombinations per photon" curves are calculated and considered in the recombination rate determinations. Observations indicating the presence of molecular activated recombination are discussed. © 1998 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.872845
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  • 8
    Digitale Medien
    Digitale Medien
    The role of particle sinks and sources in Alcator C-Mod detached divertor discharges : The 40th annual meeting of the division of plasma physics of the american physical society (1999)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 6 (1999), S. 1907-1916 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Detailed measurements of the magnitude and location of volumetric recombination occurring in the detached divertor of Alcator C-Mod tokamak [I. H. Hutchinson et al., Phys. Plasmas 1, 1511 (1994)] are presented. The drop in divertor plate ion current during detachment is due to two mechanisms: (1) volumetric recombination in the divertor plasma; and (2) reductions in the divertor ion source. Depending on plasma conditions, each of these can be the primary mechanism for the observed ion current reduction in detachment. The ion source during detachment is inferred and its magnitude is consistent with the measured divertor power flow. A scaling of the density in the divertor recombining region for L- (low confinement) mode plasmas is found, ne,r∝n¯e〈sup ARRANGE="STAGGER"〉0.8⋅PSOL2/7. A model based on pressure variation along a flux surface during detachment is consistent with the main features of this scaling. © 1999 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.873448
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  • 9
    Digitale Medien
    Digitale Medien
    Mode conversion electron heating in Alcator C-Mod: Theory and experiment : The 41st annual meeting of the division of plasma physics of the american physical society (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 1886-1893 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Localized electron heating [full width at half maximum of Δ(r/a)(approximate)0.2] by mode converted ion Bernstein waves (IBW) has been observed in the Alcator C-Mod tokamak [I. H. Hutchinson et al., Phys. Plasmas 1, 1511 (1994)]. These experiments were performed in D(3He) plasmas at high magnetic field (B0=7.9 T), high-plasma density (ne0≥1.5×1020 m−3), and for 0.05≤nHe-3/ne≤0.30. Electron heating profiles of the mode converted IBW were measured using a break in slope analysis of the electron temperature versus time in the presence of rf (radio frequency) modulation. The peak position of electron heating was found to be well-correlated with 3He concentration, in agreement with the predictions of cold plasma theory. Recently, a toroidal full-wave ion cyclotron range of frequencies (ICRF) code TORIC [M. Brambilla, Nucl. Fusion 38, 1805 (1998)] was modified to include the effects of IBW electron Landau damping at (k⊥ρi)2(very-much-greater-than)1, This model was used in combination with a 1D (one-dimensional) integral wave equation code METS [D. N. Smithe et al., Radio Frequency Power in Plasmas, AIP Conf. Proc. 403 (1997), p. 367] to analyze these experiments. Model predictions were found to be in qualitative and in some instances quantitative agreement with experimental measurements. A model for mode conversion current drive (MCCD) has also been developed which combines a toroidal full wave code with an adjoint evaluation of the ICRF current drive efficiency. Predictions for off-axis MCCD in C-Mod have been made using this model and will be described. © 2000 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.874012
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  • 10
    Digitale Medien
    Digitale Medien
    Spin configuration of Gd clusters and thin films (abstract) : The 41st annual conference on magnetism and magnetic materials (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 81 (1997), S. 5542-5542 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Studies of the magnetism and structure of Gd clusters and surfaces will be presented.1 The spin configuration of a Gd13 cluster and the Gd(0001) surface has been examined using electronic structure calculations as well as a Heisenberg model. Structural calculations show that the ground-state geometry of the cluster has a hcp arrangement with a slightly reduced nearest-neighbor distance compared to bulk and an average moment of 7.8 μB/atom. The Heisenberg model is calculated using a Ruderman-Kittel-Kasuya-Yosida-like interaction. The effects of competing ferromagnetic and antiferromagnetic coupling for the nearest- and next-nearest neighbor interaction, respectively, is investigated. It is shown that for a range of interaction strengths the spins in the cluster assume a canted configuration. This effect leads to lower net magnetization of the cluster, and accounts for the anomalous low moments of Gdn clusters that have been experimentally observed. A similar model of the Gd(0001) surface agrees well with earlier spin resolved low-energy electron diffraction experiments from Gd/W(110), and spin resolved secondary electron spectroscopy studies of the surface magnetism of Gd grown on Y(0001) will be presented. © 1997 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.364654
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