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  • 1
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The transformations of glassy Pd60U20Si20 alloys into an icosahedral state with quasicrystalline order and into the crystalline state have been studied by differential scanning calorimetry and X-ray diffraction. In addition, the electrical resistivity, the Hall coefficient and the magnetic susceptibility have been measured to high temperatures. The electronic structure has been investigated by photoelectron spectroscopy and the top surface layers have been probed by ion scattering spectroscopy. The physical properties in the icosahedral and glassy phase are similar. Comparisons with other uranium rich or dilute alloys are made in order to study the valence change or the development of a magnetic moment for uranium. Finally, the novel scanning tunneling microscope has been used to study the topography and the local tunneling barrier height with the aim of correlating micromorphology with local chemical structure.
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 3782-3787 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We describe our cryogenic magnetic force microscope, operating between 4.2 and 300 K, in fields of 0–8 T. The system uses a fiber optic interferometer to measure cantilever deflections, permitting the tracking of the resonance frequency through the use of a phase locked loop. Piezoelectric positioners, capable of operation in high magnetic fields, perform in situ tip and fiber approaches. As an effective means of vibration isolation, we suspend the microscope from a soft bellows which attenuates vibrations by more than an order of magnitude. A detailed noise analysis indicates that although the microscope is thermally limited, the system frequency resolution is currently limited by the shot noise of the interferometer. © 2000 American Institute of Physics.
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  • 3
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We describe the principles of dissipation measurements, discuss various eddy current damping mechanisms, give a brief review of a model for magnetoelastic dissipation due to domain-wall width oscillations, and present some applications of magnetic dissipation force microscopy to magnetic materials. Energy dissipation is measured by simultaneous monitoring of the damping of an oscillating cantilever and the shift in resonant frequency in a magnetic force microscope. Magnetoelastic dissipation is caused by tip-field-induced domain-wall width oscillations through magnetostriction effects. Magnetoelastic damping is strongly correlated with micromagnetic structures and allows different domain walls (such as Bloch and Néel walls) to be distinguished. © 1998 American Institute of Physics.
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  • 4
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Direct imaging of ultrathin organic films on solid surfaces is important for a variety of reasons; in particular, the use of such films as ultrathin resists for nanometer scale fabrication and information recording requires that we understand their microstrucure. We have used the Langmuir–Blodgett technique to prepare monolayer and submonolayer films of poly(octadecylacrylate) (PODA) and poly(methylmethacrylate) (PMMA) on graphite substrates. Atomic scale images obtained with the scanning tunneling microscope (STM) and the atomic force microscope of the PODA films showed a variety of structures, including isolated narrow fibrils, parallel groups of fibrils, and an ordered structure consistent with the side chain crystallization expected with that material. The fibrils observed are interpreted as individual polymer chains or small bundles of parallel chains. Images of the PMMA samples show no ordered regions. By applying voltage pulses on the STM tip, we were able to locally modify and apparently cut through the PODA fibrils.
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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 6787-6789 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Using our cryogenic magnetic force microscope, we have investigated a superconducting Nb thin film, 100 nm in thickness with Tc∼6.5 K. The film is patterned with a square array (1 μm×1 μm) of antidots, which serve as artificial pinning centers for magnetic flux. We have observed flux lattice matching as a function of applied magnetic field and temperature, for field strengths up to the third matching field, with evidence of flux dragging by the tip around the antidots. Force gradient distance curves acquired at temperatures about Tc clearly demonstrate an observable Meissner force between tip and sample, and allow for an estimation of the magnetic screening penetration depth. © 2001 American Institute of Physics.
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  • 6
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 71 (1997), S. 279-281 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A method of measuring magnetic dissipation on a sub-100 nm scale is presented. This technique relies on measuring changes in the damping of the oscillating tip in a magnetic force microscope (MFM). Damping contrast is strongly correlated with micromagnetic structure and in the case of NiFe, is in quantitative agreement with magnetoelastic losses in the sample. On recording tracks, large damping signals are observed. This has direct consequences on the interpretation of traditional MFM images acquired with detectors that convolute frequency and damping information. © 1997 American Institute of Physics.
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  • 7
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 60 (1992), S. 2741-2743 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: It is demonstrated that due to inevitable intrinsic imperfections in the microfabrication process of atomic force microscopy (AFM) tips, images of rough surfaces can be totally dominated by tip artifacts. These images reflect the mesoscopic tip shape as concluded from a comparison of AFM and scanning electron microscopy images of the tip and sample. These tip artifacts have been found on a scale of 20–600 nm, showing the necessity of characterizing the tip shape in order to make reliable sample-specific statements.
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  • 8
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 83 (1998), S. 5922-5926 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: This article presents a general treatment of magnetic dissipation due to domain wall width oscillation via magnetostriction in magnetic samples. The domain wall width is modeled as a harmonic oscillator. The parameters governing this oscillator (effective mass, stiffness, damping coefficient and driving force) are derived and expressed in terms of intrinsic magnetic parameters of magnetic materials. The magnetostriction induced damping of wall width oscillations is frictional in nature. An external ac magnetic field serves as a driving force of the oscillator. It is found that the response to the driving force depends very much on the micromagnetic structures of the magnetic domain wall. Different micromagnetic structures lead to different magnetic dissipation for a given external field. Besides giving a quantitative microscopic explanation to magnetic dissipation data measured by magnetic dissipation force microscopy, this theory predicts two new phenomena: one is that there is a minimum driving force for the wall width to oscillate and the other is a new resonance phenomenon, domain wall width resonance. © 1998 American Institute of Physics.
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  • 9
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 81 (1997), S. 5024-5024 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report the first direct measurement of local magnetic dissipation by magnetic force microscopy (MFM). A variation in dissipation of less than 10−17 W can be observed. This allows the determination of the strength of pinning sites and the variation in domain wall dampening on a sub-100 nm scale. We use a standard thin film coated Si3N4 MFM force sensor vibrated exactly at resonance. When close to the sample, the magnetic tip exerts a highly localized alternating magnetic field. Magnetic energy dissipation in the sample leads to dampening of the cantilever oscillation. The frequency, phase, and amplitude of the cantilever oscillation is measured with a dedicated phase-lock-loop circuit. The change in driving signal amplitude is directly proportional to the energy dissipation if the drive signal phase is constant. Constant force gradient and dissipation images are acquired simultaneously. By changing the tip–sample spacing, the magnitude of the tip magnetic field influencing the sample can systematically be varied. We demonstrate the potential of this technique by imaging local variations of dissipation in 4 nm thin sputtered Co films with Hc=178 Oe and in 30 nm Permalloy samples with Hc=2 Oe. In both cases a variation on a sub-100 nm scale with strong correlations between the simultaneously measured domain structure and the dissipation images is observed. As expected, dissipation is strongly dependent on the magnitude of the tip field. We also observe that the magnitude of the dissipation depends strongly on the sign of the magnetic interaction. The dissipation observed at Néel walls with attractive tip–sample interaction is larger than the dissipation at repulsive walls. © 1997 American Institute of Physics.
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  • 10
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this paper the properties of force sensors suitable for magnetic force microscopy (MFM) made by coating silicon microcantilevers with various thin magnetic films are analyzed. These MFM force sensors are batch fabricated and their magnetic properties controlled by choosing appropriate coatings. Theoretical calculations show that thin-film MFM tips have a significantly reduced stray field, a good signal-to-noise ratio, and yield improved resolution when compared to etched wire tips. The sample perturbation due to the tip stray field is small, allowing the imaging of low-coercivity samples such as Permalloy.
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