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  • 1
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report on reflected high-energy electron-diffraction and transmission electron microscopy plane-view investigation of the dislocation structure in doped and undoped ZnSe/GaAs(001) grown by molecular-beam epitaxy and metal-organic vapor-phase epitaxy. The thicknesses of the investigated layers vary between 60 and 900 nm. Several stages of dislocation formation are found which occur at distinct layer thicknesses. Frank partial dislocations (up to 500 nm), Shockley partial dislocations (between 130 and 400 nm) with a maximum density at 300 nm, and perfect 60° dislocations (above 300 nm) are observed in samples with perfectly smooth surface. The formation of Shockley partial dislocations is strongly anisotropic which might be due to the higher mobility of α-type dislocations. An increased roughness of the growing surface yields a suppression of Shockley partial dislocations and an irregular dislocation network with dislocations inclined to the 〈110〉 directions. A regular dislocation network with straight dislocations is found in Cl-doped samples. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Magnetic circular dichroism (MCD) studies at K and L edges using hard and soft x rays are presented. The relation of this universal phenomenon in the x-ray absorption near-edge structure (XANES) and extended x-ray absorption fine structure (EXAFS) regions to local magnetic structures in the case of 3d and 4f elements is illustrated. The validity of atomic and band-structure pictures to describe the MCD in the XANES range are outlined and the applicability of sum rules and two-step vector coupling models to deduce spin and orbital moments of the absorbing atom as well as spin-density profiles from the experimental data are critically discussed. The correlation of the dichroic contribution in the EXAFS to the magnetic moments and spin densities of the neighboring atoms are addressed by systematic studies which provide new insights into the exchange phenomena of the interaction of spin-polarized electrons with ferromagnetic media. The potential but also the limitations of this new spectroscopy is demonstrated.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 7162-7164 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The magnetization reversal of an array of 1 μm squared FeGd dots has been studied by magnetic transmission x-ray microscopy (MTXM). A (4 Å Fe/4Å Gd)×75 multilayered FeGd system has been prepared on a 30 nm thin Si3N4 membrane by sputtering and structured by optical lithography and ion beam etching techniques. Both the domain structure within each single dot and the collective switching behavior could be observed with MTXM. A large variation in the nucleation field of the dots was found and can be attributed to the shape of the dots. A correlation between the nucleation field and the perimeter of each dot could be deduced. Hysteresis loops of individual dots are derived, taking into account the proportionality of the dichroic contrast to the magnetization of the sample. The stepped profile of the magnetization loop of a single dot is found to be clearly distinct from a continuous film. The high lateral resolution and the possibility to record the images in varying external magnetic fields proves that MTXM is a highly adapted tool to investigate nanostructured magnetic systems. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 7159-7161 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Magnetic transmission x-ray microscopy is a novel technique to image element specifically magnetic domain structures. A lateral resolution down to 25 nm is provided by the Fresnel zone plates used as optical elements in soft x-ray microscopy. The magnetic contrast is given by x-ray magnetic circular dichroism, i.e., large magnetic contributions up to 25% to the absorption cross section of circularly polarized x rays that occur in the vicinity of, e.g., the Fe L3,2 edges (706 and 719 eV) and depend on the relative orientation of the projection of the magnetization of the sample onto the photon propagation direction. Thus, both in-plane and out-of-plane contributions to the magnetization are accessible. Here we present images of the magnetic domain structure of a (3 nm Cr/50 nm Fe/6 nm Cr) thin film system with a preferentially in-plane magnetization recorded at the Fe L edges. The samples have been prepared by thermal evaporation onto a 100 nm thin Si3N4 membrane and were mounted under a tilt of 30° with respect to the transmission direction of the photons in the full-field microscope. Corresponding images taken under a tilt of 0° ruled out out-of-plane contributions. Images recorded in applied varying external magnetic fields allowed to study the switching behavior. These trial results have a large impact on further investigations of nanostructured magnetic systems, e.g., spintronic devices and magnetic sensors with magnetic soft x-ray microscopy. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 6478-6480 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A multilayered FeGd system sputtered on a Si3N4-membrane was used to demonstrate that magnetic transmission x-ray microscopy enables the imaging of the domain structure with high resolution in a quantitative way and in varying external magnetic fields. The field-dependent evolution of sub-100 nm out-of-plane magnetized domains, i.e., the transition from stripe into bubble domains, could be observed in detail. It has been shown that critical fields like the bubble collapse field can be described by a wall energy model. Contrary to the assumption of the theory, the magnetization does not remain perpendicular to the film plane in all cases. This is only true inside the bubbles. In the stripe domains the magnetic moments rotate. Their angle could be measured as a function of the external applied field. Internal stray fields can cause a rotation of moments leading to a contrast at the edges of stripe domains. The results indicate that the magnetization reversal in 3d/4f multilayers is not only determined by wall motions and is therefore more complex than previously assumed. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The method of spin-dependent absorption has been used to examine the temperature dependence of the circular magnetic x-ray dichroism (CMXD) of the (disordered) Invar alloy fcc Fe72Pt28. At the Fe K edge the difference of the transmission for the reversed magnetization direction was determined with an accuracy of 10−5. By comparing the dichroic effects at 110 and at 410 K evidence was found for a temperature-dependent change of the magnetic absorption profile different from the pure amplitude reduction due to the reduced magnetization. It indicates a change of the spin splitting in the low-lying unoccupied p states. The polarization-averaged absorption spectrum shows also a small variation between 4 and 11 eV above the threshold indicating that the p-like electron density drops when the sample is heated. The experimental CMXD profiles are compared with spin-polarized band-structure calculations for ordered Fe3Pt and discussed within the frame of the model of high-spin–low-spin transitions in the Invar regime.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 5346-5346 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The interference of charge and magnetic scattering from ferromagnetic targets leads in case of circularly polarized x rays to a relative difference (flipping ratio) of the Bragg peak intensity in the order of 10−3, when the magnetization aligned in the scattering plane is reversed (spin-dependent scattering). We have measured the spin-dependent scattering in Fe, Gd, and Tb polycrystalline metallic foils using circularly polarized synchrotron radiation. From the data, magnetic form factors have been deduced. As demonstrated for Gd and Tb, from the flipping ratios the orbital and spin contribution can be directly separated by varying the angle between the scattering vector and the sample magnetization. Spin-dependent resonance scattering has been studied at the K edge of a Ni single crystal. A significant enhancement of the magnetic scattering amplitude compared to the magnetic resonance scattering of linearly polarized light and sample magnetization perpendicular to the scattering plane has been observed. A strongly increased nonresonant magnetic scattering with opposite sign compared to the resonant magnetic effects is observed in the preedge energy region below −10 eV with respect to the K-absorption onset. The applicability of magnetic scattering using circularly polarized synchrotron radiation for the investigation of ferromagnetic media especially in view of its complementarity to neutron studies is discussed.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 6147-6149 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The spectroscopy of spin-dependent absorption using circularly polarized synchrotron radiation is a new method to study the magnetic structure of multicomponent systems. We demonstrate for substitutional 5d transition-metal impurities in an iron host that from L2,3 spin-dependent absorption signal information on the local magnetic moment, carried by the d electrons of the absorbing atom, can be deduced. The experimentally determined local magnetic moments of the 5d impurities in Fe are in good agreement with the theoretical results based on the spin-polarized relativistic Korringa–Kohn–Rostoker–Green function method of band-structure calculation. The presented data are−to our knowledge−the first experimental proof of the change from antiferro- to ferromagnetic coupling between Os and Ir, which has been predicted by the above-mentioned calculations.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 4456-4458 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The spin dependence of L2,3 absorption in 5d atoms oriented in a ferromagnetic matrix contains information on the spin density of the empty d-projected states of the absorbing atom. Spin-dependent absorption spectroscopy using circularly polarized synchrotron radiation was applied to study the polarization of the Pt atoms in the binary alloy Co50Pt50 and Pt/Co layered structures, which are promising candidates for magneto-optical recording. The spin-dependent absorption signals for vapor-deposited 250(4 A(ring) Co+18 A(ring) Pt) and 250(6 A(ring) Co+18 A(ring) Pt) multilayers indicate a ferromagnetic coupling on Pt and Co atoms with a significant Pt polarization. This is reduced on average by about 60% with respect to the Pt polarization in the Co50Pt50 alloy. The experimental results are discussed on the basis of spin-polarized band-structure calculations.
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Circular magnetic x-ray dichroism (CMXD) was observed at the Pt and Ir L2,3 edges in the multilayered structures 25⋅(4 A(ring) Co+30 A(ring) Pt) and 25⋅(4 A(ring) Co+11 A(ring) Pt+8 A(ring) Ir+11 A(ring) Pt). The samples were prepared by sputtering and show a large perpendicular anisotropy. The magnetic absorption at the Pt and Ir L2,3 edges was measured in an external magnetic field of 0.15 T perpendicular to the surface. The results indicate a significant spin polarization of the Pt and Ir layers. By comparison with the corresponding CMXD signals of Pt and Ir impurities in a ferromagnetic iron host we estimated the local spin and orbital moments. The results show that the innermost three monolayers in both systems couple ferromagnetically to the Co layers with an average magnetic moment of about 0.01 μB.
    Type of Medium: Electronic Resource
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