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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 7248-7250 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Measurements of the major hysteresis loop and of the temperature dependence of the field cooled and zero field cooled moment in applied fields less than the coercive field have been performed on two ferromagnetic perovskites La0.95Mg0.05MnO3 and La0.5Sr0.5CoO3. The data have been analyzed within the framework of a generalized Preisach model which includes thermal fluctuations, critical effects, and a temperature dependent distribution of free energy barriers. The analysis shows that the response functions of the manganese perovskite are dominated by the growth of the anisotropy barriers, while in the cobalt perovskite, thermal fluctuations and barrier growth play a roughly equal role. © 2001 American Institute of Physics.
    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 87 (2000), S. 4786-4788 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Measurements of the initial magnetizing curve, the magnetizing remanence, the descending branch of the major hysteresis loop, and the demagnetizing remanence have been performed on a reentrant ferromagnet Fe0.65Ni0.23Cr0.12, at several temperatures in the vicinity of the postulated ferromagnetic-spin glass "reentrant transition." Henkel plots of the principal magnetizing and demagnetizing remanences show a systematic change in curvature with temperature, from a "high temperature" regime T≥8 K where the curvature is predominantly magnetizing-like to a "low temperature" regime T≤6 K where the curvature is purely demagnetizing-like. Numerical simulations based on a Preisach model which includes thermal fluctuations show that this behavior is consistent with a physical picture of coupled bistable subsystems with a temperature dependent distribution of interaction fields, which evolves with decreasing temperature from a regime dominated by long range ferromagnetic interactions to a regime in which the interaction fields fluctuate randomly about a zero mean. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 71 (1997), S. 2211-2213 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report results on the activation field and frequency dependence of the coercive voltage in epitaxial ferroelectric thin film capacitors. Frequency dependent hysteresis loops and pulse width dependent polarization of epitaxial La0.5Sr0.5CoO3/(Pb,La)(Zr,Ti)O3/La0.5Sr0.5CoO3 capacitor structures were measured as a function of La content. The coercive voltages and their frequency dependence vary systematically with increasing La content. We show that the activation field for polarization reversal is directly related to the c/a ratio (tetragonality ratio) of the ferroelectric layer. A larger c/a ratio leads to a larger field to activate the motion of domain walls through the lattice. An important consequence of a larger activation field is a stronger pulse width dependence of the pulse switched polarization. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 69 (1996), S. 3839-3841 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Radio-frequency magnetron sputtering was used to deposit SrBi2Ta2O9 ferroelectric thin films on Pt(111)/Ti/SiO2/Si(001) substrates. Thin films were deposited at room temperature with argon pressures of 0.5–100 mTorr and with sputtering power of 2.5 W/cm2. The crystal orientations of thin films were strongly affected by the argon pressures, the c-axis oriented SrBi2Ta2O9 thin film was obtained with argon pressure of 30 mTorr. The crystal structures of the c-axis oriented SrBi2Ta2O9 thin film were investigated by x-ray diffraction methods: θ-2θ scan, rocking curve, and φ scans. The well aligned microstructure was observed with the average grain size of about 2000 A(ring) in an atomic force microscopic image. Ferroelectric properties were observed for the c-axis oriented thin film: Pr*−PrΛ and Ec were 9.7 μC/cm2 and 50 kV/cm, respectively, with excitation voltage of 3 V. © 1996 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 83 (1998), S. 1617-1624 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In earlier publications, we have demonstrated that La0.5Sr0.5CoO3 electrodes dramatically improve the phase stability and electrical properties of lead based ferroelectric capacitors. This study evaluates the influence of deviation from the cationic stoichiometry, La/Sr=1, on the ferroelectric properties. Polycrystalline Pb(Nb0.04Zr0.18Ti0.78)O3 based capacitors were fabricated with La0.5Sr0.5CoO3 as the bottom electrode and either La0.5Sr0.5CoO3 or La0.85Sr0.15CoO3 as the top electrode. The as-grown capacitors with La0.85Sr0.15CoO3 as the top electrode were slightly asymmetric about the voltage axis. However, the asymmetry did not increase when the capacitors were subjected to single side pulses and temperature. Both capacitor structures showed good fatigue (no fatigue up to 1011 cycles), retention, and imprint characteristics. Detailed pulse width and voltage dependent measurements were also carried out to further understand the impact of the change in electrode composition. The polarization values at 1 μs pulse width were as large as 13 μC/cm2, though the dependence was steeper for capacitors with asymmetric electrodes. The resistance to switching during polarization reversal, formally termed activation field, α, was measured from the switching current dependence of the applied field. These values were slightly larger for the capacitors with asymmetric electrodes. The data indicate that the ferroelectric properties of the capacitor are almost not influenced by a change of the top electrode from La0.5Sr0.5CoO3 to La0.85Sr0.15CoO3.© 1998 American Institute of Physics.
    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 83 (1998), S. 2165-2171 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have investigated the imprint characteristics of fully integrated ferroelectric lead zirconate titanate based capacitors. These capacitors were fabricated using conducting perovskite La–Sr–Co–O electrodes. We have specifically focused on the effect of several test and capacitor variables, including temperature, unipolar stress amplitude, number of cycles, and device area. Two different figures of merit, one based on coercive voltage changes and the other based on differences in polarization values were used to quantify imprint. The imprint in our capacitors showed a small temperature dependence over the range that we have studied. The unidirectional pulse voltage amplitude had a larger influence on the imprint. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 72 (1998), S. 3300-3302 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report results of high-speed polarization relaxation measurements in ferroelectric thin film capacitors. Polarization relaxation has been reported to occur in two distinct time regimes, one for relaxation times in the range of a few milliseconds and a second for longer relaxation times. We find that the polarization relaxation in the first regime is governed by at least two different physical processes, namely depoling fields and the activation field for switching. Using prototypical epitaxial PbZr0.2Ti0.8O3 and Pb0.9La0.1Zr0.2Ti0.8O3 test capacitors, we demonstrate the effect of film microstructure and switching speed on the relaxation dynamics in the first regime. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 71 (1997), S. 356-358 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A high density ferroelectric memory process flow requires the integration of conducting barrier layers to connect the drain of the pass-gate transistor to the bottom electrode of the ferroelectric stack. We are studying the effect of crystallinity of the TiN/Pt barrier layer with Si wafers on the ferroelectric properties of La0.5Sr0.5CoO3/Pb(Nb0.04Zr0.28Ti0.68)O3/La0.5Sr0.5CoO3 (LSCO/PNZT/LSCO) capacitors. Structural studies indicate complete phase purity (i.e., fully perovskite) in both epitaxial and polycrystalline materials. The polycrystalline capacitors show lower remnant polarization and coercive voltages. However, the retention, fatigue, and imprint characteristics are similar, indicating minimal influence of crystalline quality on the ferroelectric properties. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 71 (1997), S. 3578-3580 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report low voltage (1.5–3 V) performance of ferroelectric Pb(Zr,Ti)O3 based capacitors. La substitution up to 10% was performed to systematically lower the coercive and saturation voltages of epitaxial ferroelectric capacitors grown on Si using a (Ti0.9Al0.1)N/Pt conducting barrier composite. Ferroelectric capacitors substituted with 10% La show significantly lower coercive voltage compared to capacitors with 0% and 3% La. This is attributed to a systematic decrease in the tetragonality (i.e., c/a ratio) of the ferroelectric phase. Furthermore, the samples doped with 10% La showed dramatically better retention and pulse width dependent polarization compared to the capacitors with 0% and 3% La. These capacitors show promise as storage elements in low power high density memory architectures. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 3366-3368 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report the activation field characteristics of (La,Sr)CoO3/Pb(Nb,Zr,Ti)O3/(La,Sr)CoO3 capacitors with areas varying from 13 to 9600 μm2. Switching properties such as maximum current and switching time depend on the capacitor area and measuring circuit elements, but the activation field is independent of capacitor area and measuring circuit parameters. Area independence of activation fields is also confirmed in (Pb,La)(Zr,Ti)O3 thin film capacitors. Two different approaches have been used to determine the activation field, yielding similar results. It is concluded that activation field is an intrinsic property and is a good quantitative measure of the ferroelectric switching properties. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
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