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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 6338-6340 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Thin films (≈0.4 μm) of cobalt ferrite (CoFe2O4) have been grown on single-crystal (100) MgO substrates using pulsed laser deposition (PLD). The phase, orientation, and microstructure of the as-deposited films were investigated as a function of substrate temperature (i.e., 200–800 °C) at a constant oxygen deposition pressure of 30 mTorr. The as-deposited films were found to be single phase, well oriented, and approximately matching the stoichiometry of the target, but the cubic lattice constant of the films depended on the substrate temperature indicating that the films were strained. The greatest effect of the substrate temperature was on the magnetic properties of the as-deposited films. At 800 °C, 4πMs was measured to be 5370 G which is approximately the accepted bulk value for cobalt ferrite. In addition, PLD cobalt ferrite films grown at substrate temperatures of 600 and 800 °C exhibited a uniaxial magnetic anisotropy with an easy direction normal to the film plane. Films grown at 200 and 400 °C also exhibited a uniaxial magnetic anisotropy but possessed a planar easy direction. © 1996 American Institute of Physics.
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  • 2
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Ferromagnetic resonance (FMR) can reveal important information on the size and shape of the ferromagnetic particles which are dispersed in granular giant magnetoresistive (GMR) materials. We have investigated the FMR spectra of three different types of granular GMR material, each with different properties: (1) melt-spun ribbons of Fe5Co15Cu80 and Co20Cu80, (2) thin films of Co20Cu80 produced by pulsed laser deposition, and (3) a granular multilayer film of [Cu(50 A(ring))/Fe(10 A(ring))]×50. We interpret the linewidth of these materials in as simple a manner as possible, as a "powder pattern'' of noninteracting ferromagnetic particles. The linewidth of the melt-spun ribbons is caused by a completely random distribution of crystalline anisotropy axes. The linewidth of these samples is strongly dependent upon the annealing temperature: the linewidth of the as-spun sample is 2.5 kOe (appropriate for single-domain particles) while the linewidth of a melt-spun sample annealed at 900 °C for 15 min is 3.8 kOe (appropriate for larger, multidomain particles). The linewidth of the granular multilayer is attributed to a restricted distribution of shape anisotropies, as expected from a discontinuous multilayer, and is only 0.98 kOe with the magnetic field in the plane of the film.
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  • 3
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The results of ferromagnetic resonance experiments on 10 nm polycrystalline films of Fe with very thin surface layers of Ni and Co, using Si and a high temperature superconductor (YBCO) as substrates is reported herein. An earlier fmr investigation of Fe films on YBCO showed strongly temperature dependent linewidths and resonance fields but only small effects in Fe on Si. In this work, the resonance of Fe on Si is found to be significantly narrower when the Fe film has thin (0.5 to 1.0 nm) Ni surface layers, compared to uncoated Fe; linewidths are as narrow as 15 Oe at 9 GHz. However, when YBCO substrates are used, the iron resonance properties are nearly the same as in the case where no Ni was used. This indicates that the effects seen in earlier work were not the result of an oxide layer on the Fe but may indicate a magnetically active surface layer in the YBCO. Co surface layers have the effect of producing strongly temperature dependent anisotropies and linewidths on all substrates used, with the strongest temperature dependence near 160 K, possibly caused by the ordering of an antiferromagnetic surface layer.
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 6622-6622 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have investigated the ferromagnetic resonance (FMR) spectra of several granular alloys displaying giant magnetoresistance (GMR). For this task, we have produced melt-spun ribbons of Fe5Co15Cu80 and Co20Cu80 by rapid quenching and thin films of Co80Cu20 by pulsed laser deposition. The salient feature of the FMR spectra is the increase of the resonance linewidth as a function of increasing annealing temperature. We have deconvoluted the FMR spectra to a single-domain powder pattern and a multidomain powder pattern. As a function of annealing temperature, the GMR of these samples attains a maximum value. Near the peak of the GMR curve, the FMR spectrum reveals that the ferromagnetic particles are half mono- and half multidomain. Since the maximum size of a single-domain particle is known, this enables us to estimate the spin diffusion length of the Cu conduction electrons. We have also demonstrated, theoretically and experimentally, that the appropriate demagnetizing field to apply to the ensemble of spherical magnetic particles that comprise our granular thin film is simply the field corresponding to the average magnetization.
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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 81 (1997), S. 6884-6891 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Thick films (10–12 μm) of NiZn–ferrite (Ni0.6Zn0.4Fe2O4) were grown on single-crystal (100) magnesium oxide substrates using pulsed laser deposition (PLD). The morphology, phase, orientation, strain, and magnetic properties of the as-deposited films were investigated as a function of substrate temperature (400–700 °C) and O2 background pressure (50–200 mTorr). Compositional analysis shows that the PLD NiZn–ferrite films are about 45% Zn deficient when grown using a standard polycrystalline single phase Ni0.4Zn0.6Fe2O4 target regardless of substrate temperature or O2 pressure. However, Zn-rich targets were successfully used to compensate for the Zn deficiency in the NiZn–ferrite films. PLD NiZn–ferrite films grown at 700 °C exhibit the highest degree of crystalline quality and nearly bulk saturation magnetization values (i.e., 5000 G). At low O2 pressures (〈75 mTorr) the films, which were grown at 700 °C, are under a significant compressive stress. The stress decreases when the PLD NiZn–ferrite films are grown in higher O2 pressures but the crystalline quality and surface morphology deteriorate. The compressive stress produces a planar anisotropy field of about 1000–3500 Oe depending on the O2 pressure, which is consistent with the stress results from x-ray diffraction measurements on the NiZn–ferrite films. It is hypothesized that the film stress is largely the result of oxygen loss from the films during deposition. © 1997 American Institute of Physics.
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  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 3517-3520 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The thermal expansion coefficients along the a axis (αa) and c axis (αc) of barium hexaferrite were measured from room temperature to 850 °C. The thermal expansion of barium hexaferrite along the a axis and c axis was found to be linear as a function of temperature, indicating constant thermal expansion coefficients over this temperature range. The specific values for αc and αa were calculated to be 12.2±0.9 and 9.99±1.1 ppm/°C, respectively. The measurements were performed using a standard x-ray powder diffraction setup equipped with a high temperature stage. © 1996 American Institute of Physics.
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  • 7
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 68 (1997), S. 3872-3876 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: High-quality superconducting films have been deposited onto 2 in. diameter substrates in a large-area pulsed laser deposition (PLD) system incorporating a novel pseudoblackbody radiation heater. A KrF laser (λ=248 nm) was rastered across the radius of a rotating target and a slot in the blackbody heater collected the ablation plume onto a rotating substrate holder. Critical temperatures of 〉90 Kwith critical current densities of 2–4 MA/cm2 were measured across a 2 in. diam YBa2Cu3O7−δ(YBCO) film deposited on an LaAlO3(LAO) substrate. Metal atom concentrations were measured by Rutherford backscattering spectrometry to be nearly stoichiometric and the film thickness uniformity was ±7% about the mean. Purely c-axis orientation was observed in the x-ray diffraction patterns. A multilayer LAO/YBCO film was deposited in situ on an MgO substrate using a large-area target load-lock chamber and exhibited good crystalline quality. YBCO films deposited onto both sides of a 1 in. square by 0.010-in.-thick MgO substrate were patterned and fabricated into a four-channel microwave receiver operating near 10 GHz. The receiver exhibited low loss and good frequency selectivity at 77 K. © 1997 American Institute of Physics.
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  • 8
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 91 (2002), S. 5371-5376 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Highly oriented indium tin oxide (ITO) thin films were grown by pulsed-laser deposition (PLD) on glass and single-crystal yttria-stabilized zirconia (YSZ) substrates. The structural, electrical, and optical properties of these films were investigated as a function of oxygen partial pressure. Films were deposited at substrate temperature of 300 °C in mixed gases (12 mTorr of argon and 1–50 mTorr of oxygen) using a KrF excimer laser (248 nm and 30 ns full width at half maximum) at a fluence of 1.2 J/cm2. ITO films (300 nm thick), deposited by PLD on YSZ at 300 °C in a gas mixture of 12 mTorr of argon and 6 mTorr of oxygen, exhibit a low electrical resistivity (1.6×10−4 Ω cm) with a high transparency (∼74%) at 550 nm. ITO films deposited on both glass and YSZ substrates have been used as an anode contact in organic light-emitting diodes. A comparison of the device performance for the two substrates shows that the device fabricated on the ITO/YSZ has a higher external quantum efficiency than that of the device fabricated on the ITO glass.
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  • 9
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The emitted particles from pulsed-laser ablation (PLA), λ=193 nm and fluence=88–400 mJ/cm2, of frozen glycerol was examined using time-of-flight mass spectrometry. The data are analyzed using supersonic molecular-beam theory and the result is interpreted using a thermal/fluid-dynamic model. Both intact and fragmented glycerol are emitted in the PLA process at all fluences and their concentration ratio is fluence dependent. Fragmentation occurs predominantly at one of the C–C bonds forming CH2–OH (31 amu) and HO–CH2–CH–OH (61 amu). CH3 is produced at the target which requires the protonation of a CH2 fragment. At fluences higher than 250 mJ/cm2, ions are detected. These ions have very high velocity, 〉2000 m/s, and their intensity increases with fluences. PLA is thus not suitable for glycerol transfer under these conditions due to fragmentation. The data show that particle emission proceeds as a simple thermal vaporization process at fluences 〈200 mJ/cm2. Higher fluences will yield a Knudsen layer (KL), which is formed in front of the target surface. For fluences 〉300 mJ/cm2, particles from the KL go through unsteady adiabatic expansion prior to free flight. Models of particle and ion formation and interaction are proposed and discussed. © 2001 American Institute of Physics.
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  • 10
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 5739-5746 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Pulsed laser deposition (PLD) has been used to fabricate polymer/carbon nanocomposite thin films for use in chemical sensors (chemiresistors). Ethylene vinyl acetate copolymer (EVA) films (undoped and 20% carbon by weight) were deposited using an ArF excimer laser (193 nm) at fluences between 150 and 300 mJ/cm2. The structure and morphology of the deposited films were characterized using Fourier transform infrared spectroscopy (FTIR), Raman scattering, and transmission and scanning electron microscopy (TEM). An analysis of the FTIR spectra indicates that a film deposited using an undoped EVA target is primarily polyethylene, suggesting that the acetate group is photochemically or photothermally removed from the starting material. Gas phase measurements of the laser-evaporated material using a quadrupole time of flight mass spectrometer confirm the production of the acetyl radical on the target surface. Analysis of TEM of films deposited using C-doped targets shows that the carbon black particles (initially 50 nm particles in 1 μm agglomerates) are broken down into particles that are ≤50 nm in the deposited film. Incorporation of carbon into the target reduces the degree of photochemical damage of the starting material, as shown in the FTIR spectra of the deposited film. The sensitivity and response time of chemiresistors fabricated from 6 μm thick composite films on top of gold electrodes were measured using toluene vapor (548 ppm). The chemiresistors exhibited a reversible and fast (〈1.3 s) response to the vapor. In comparison to data reported in the literature, chemiresistors fabricated from PLD films are significantly better than devices fabricated using a more conventional polymer film growth technique. © 2001 American Institute of Physics.
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