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  • 1
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have investigated the magnetic exchange coupling between an Fe film and an Fe(100) single crystal whisker substrate separated by varying thickness Cr or Ag spacer layers. The magnetization of the Fe was measured using scanning electron microscopy with polarization analysis. Reflection high-energy electron diffraction and scanning tunneling microscopy (STM) were used to analyze the film structure. In addition to the oscillatory thickness-dependent bilinear exchange coupling, biquadratic exchange coupling was observed in both films. At spacer thicknesses that correspond to the transitions between ferromagnetic and antiferromagnetic coupling the Fe film magnetization was in-plane and orthogonal to the ferromagnetic alignment. Our observations generally agree with the model proposed by Slonczewski1 in which the biquadratic coupling originates from the bilinear coupling through spatial fluctuations of the spacer thickness. If these fluctuations occur over small enough length scales and the bilinear coupling varies between ferromagnetic and antiferromagnetic with monolayer thickness changes, then the Fe film intralayer exchange stiffness forces biquadratic coupling of the film to the substrate. We have observed the necessary short-period coupling in both Fe/Cr/Fe and Fe/Ag/Fe and we have measured the length scale of the thickness variations on a similar sample using a STM. One unexpected result in Fe/Ag/Fe was that the amount of biquadratic coupling increased with increasing top Fe layer thickness. No similar dependence was observed for Fe/Cr/Fe.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 6201-6203 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The magnetism at the surface of a Cr film grown epitaxially on a Fe(100) whisker is observed as a function of Cr thickness by scanning electron microscopy with polarization analysis. Use of a wedge-shaped film of linearly increasing thickness allows the magnetism to be followed continuously for 75 Cr layers. Over the temperature range measured from just below the Néel temperature of bulk Cr, TN, to 1.8 TN, the surface magnetic moment is seen to persist and change direction with each additional Cr layer, but there are phase slips in this antiferromagnetic ordering. These are consistent with an incommensurate spin density wave (SDW) in the Cr film having a wavelength of 40 layers at TN. An irregularity in the antiferromagnetic stacking order in the first four layers is discussed and the behavior of the moments at the subsequent phase slip is examined. The limitations which prevent the determination of the surface magnetic moment from the spin polarization of secondary electrons are discussed.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Very little is currently known about domains and domain walls in ultrathin ferromagnetic films, i.e., films that are a few atomic layers to a few tens of layers thick. A major experimental difficulty is that these films must be grown and examined in situ with strict control over their atomic structure and elemental composition. Recently, scanning electron microscopy with polarization analysis (SEMPA) has been used to image domains in Fe1and Co2 films that were only a few monolayers thick. The structure and composition of the films were monitored during growth using RHEED (reflection high energy electron diffraction) and Auger electron spectroscopy. The magnetic structure of these films was then investigated in situ using SEMPA. SEMPA directly images the magnetization by measuring the spin polarization of secondary electrons emitted in the scanning electron microscope. This combination of surface sensitive techniques allows one to study the domain structure, anisotropy and magnetization of the films as a function of various growth parameters, such as, thickness, substrate roughness, and temperature.〈ks〉
    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 79 (1996), S. 6079-6083 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Nanostructured materials and devices will play an important role in a variety of future technologies, including magnetics. We describe a method for nanostructure fabrication based on the use of laser light to focus neutral atoms. The method uses neither a mask nor a resist, but relies on the direct deposition of atoms to form permanent structures. Since the atomic de Broglie wavelength is of picometer order, the size of structures produced is not significantly limited by diffraction, as in optical lithography. Lines as narrow as 38 nm full width at half maximum spaced by 213 nm have been produced and we have demonstrated the production of a two-dimensional array of dots. The highly parallel process of nanostructure formation and the intrinsic accuracy of the optical wavelength that determines structure spacing suggest a number of interesting applications, including calibration standards for various types of microscopy, lithography, and micromeasurement systems. Possible magnetic applications include the production of arrays of magnetic elements, laterally structured giant magnetoresistive devices, and the patterning of magnetic media.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The giant magnetoresistance and the interlayer exchange coupling between magnetic layers separated by nonmagnetic spacer layers are sensitive to the roughness at the interfaces in multilayer magnetic structures. We present scanning tunneling microscopy (STM) measurements of the thickness fluctuations in Cr films grown at different temperatures on near-perfectly flat Fe(100) whiskers and correlate these results with our scanning electron microscopy with polarization analysis (SEMPA) measurements of the oscillations of the exchange coupling in Fe/Cr/Fe(100) structures grown at similar temperatures. Layer-by-layer growth was observed by STM for Cr deposition on an Fe substrate at deposition temperatures greater than 300 °C. The SEMPA measurements of the Fe overlayer magnetization as a function of Cr spacer layer thickness for Cr growth at this temperature could be simulated well by oscillatory coupling with periods 2.105±0.005d and 12±1d, where d is the layer spacing. Rougher Cr growth, limited by diffusion kinetics, is observed at lower temperatures, giving a distribution of thicknesses in the growth front. We modeled the Fe magnetization for lower temperature Cr growth by assuming that the exchange coupling at each discrete Cr thickness is the same as found for layer-by-layer growth. The total coupling at each average Cr spacer layer thickness was determined by adding the weighted contribution to the coupling from each Cr layer thickness contributing to the average thickness. Very good agreement was obtained with the SEMPA measurement of the Fe overlayer magnetization for Cr growth at lower temperatures without including other consequences of roughness at the interface, such as the breakdown of translational invariance.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 6452-6454 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: SEMPA observations of magnetic exchange coupling in the Fe/Ag/Fe, Fe/Au/Fe, and Fe/Cr/Fe systems reveal an intensity variation in the emitted secondary electron signal that depends only on whether the Fe layers are coupled in a ferromagnetic or antiferromagnetic sense. We ascribe this new effect to spin dependence in the transport of electrons between the two magnetic layers.
    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 75 (1994), S. 6437-6439 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Scanning electron microscopy with polarization analysis was used to investigate the interlayer exchange coupling in Fe/Au/Fe(100) sandwich structures. The films were epitaxially grown on single-crystal Fe(100) substrates. Electron diffraction measurements revealed that the Au spacer film grew with a surface reconstruction consistent with that observed for bulk Au crystals. The exchange coupling oscillates between primarily ferromagnetic and antiferromagnetic coupling for Au spacer layers up to 65 layers (13 nm) thick, but a significant biquadratic coupling component was also observed. The oscillatory coupling exhibited two components with periods of 2.48±0.05 layers (0.506±0.010 nm) and 8.6±0.3 layers (1.75±0.06 nm). The measured periods are in excellent agreement with those calculated from spanning vectors of the Au Fermi surface.
    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 81 (1997), S. 4342-4342 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The magnitude and the direction of the oscillatory exchange coupling in multilayer structures depend sensitively on the atomic scale ordering of the layers. Disorder in the form of substrate roughness, interlayer thickness fluctuations, or interfacial interdiffusion can result in reduced bilinear exchange coupling, the disappearance of short period coupling oscillations, and the increase or decrease of the relative strength of the biquadratic coupling. We have investigated the effect of roughness by growing nearly perfect multilayer Fe/Cr and Fe/Au structures on single crystal Fe whisker substrates. The disorder in these structures was measured using scanning tunneling microscopy (STM) and reflection high-energy electron diffraction (RHEED), while the coupling directions and magnitudes were measured using scanning electron microscopy with polarization analysis and magneto-optic Kerr microscopy. For the nearly perfect trilayer structures, the periodicity and the magnitude of the oscillatory coupling are in agreement with theoretical predictions based on spacer layer Fermi surface properties. For rougher multilayer systems the exchange coupling can be modeled using structural information from STM and RHEED measurements.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 52 (1988), S. 1918-1920 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Scanning electron microscopy with electron polarization analysis has been used to image domains of ultrathin Fe films grown epitaxially on a Ag(100) substrate. Room-temperature measurements show clearly the existence of large domains of in-plane magnetization for film thicknesses of 3.4 monolayers or more. No in-plane domains were observed for thinner films.
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We compare measurements of magnetization profiles across a 180° surface domain wall in a 0.24-μm-thick of Permalloy (Ni81Fe19), obtained with scanning electron microscopy with polarization analysis (SEMPA) and longitudinal magneto-optic (MO) Kerr microscopy with the predictions of a bulk micromagnetic theory. Both measurement techniques yield wall profiles in accordance with the predictions of micromagnetic theory. We conclude that for micromagnetic structure with relevant length scales on the order of tens of nanometers, SEMPA and MO Kerr microscopy yield equivalent quantitative micromagnetic information within the transverse spatial resolution limits of each technique. Near-surface effects such as enhanced surface moments, weakened surface exchange, and surface anisotropy are not important in determining the surface domain wall profiles that we observe.
    Type of Medium: Electronic Resource
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