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  • 1
    Electronic Resource
    Electronic Resource
    Quantitative characterization of additional ferromagnetic phase in melt-quenched and sintered Nd–Fe–B-based magnets : The 40th annual conference on magnetism and magnetic materials (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 5513-5515 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Quantitative evidence of a ferromagnetic Fe-rich minor phase present in both melt-quenched/die-upset and sintered magnets based on the Nd2Fe14B composition is presented. Full hysteresis loops were obtained at elevated temperatures (650 K≤T≤800 K) and were subsequently decomposed to obtain the saturation magnetization Ms of the minor phase as well as the paramagnetic slope of the 2-14-1 major phase as a function of temperature. Assuming a composition of pure iron, the calculated volume % of the impurity phase in the die-upset magnets is consistent with that obtained from previous observations of the widths and geometry of the intergranular phase found in the same magnets. The magnetization of the ferromagnetic impurity phase in the melt-quenched magnets decreases more rapidly than that of pure iron; extrapolation indicates a Curie temperature in the range 925 K≤T≤975 K. The paramagnetic susceptibility of the Nd2Fe14B main phases exhibits Curie–Weiss behavior with the same paramagnetic Curie temperature for both sintered and die-upset samples. The Curie constants differ, however, probably due to the different degrees of crystallographic alignment. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.362295
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  • 2
    Electronic Resource
    Electronic Resource
    Evidence for reversal by nucleation in RE-Fe-B die-upset magnets : The 6th joint magnetism and magnetic materials (MMM)-intermag conference (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 6235-6237 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Electron microscopy and initial magnetization studies at elevated temperatures were performed on two die-upset rare-earth magnets with bulk compositions Nd13.75Fe80.25B6 and Pr13.75Fe80.25B6. In both compositions the intergranular phase is amorphous and occurs primarily on those surfaces parallel to the tetragonal 2-14-1 phase c axis. The intergranular phase is enriched in iron relative to the bulk grain, with an average width of 8–12 A(ring) in the Nd-based magnet and 15–20 A(ring) in the Pr-based magnet. The initial magnetization curves and the dependence of the coercivity upon maximum magnetizing field both increase linearly with a common slope and then saturate, consistent with nucleation-dominated behavior. These results suggest that the dominant reversal mechanism in these magnets is nucleation of reversed domains in the iron-rich intergranular region of reduced anisotropy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.358291
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  • 3
    Electronic Resource
    Electronic Resource
    Modeling of permanent magnets: Interpretation of parameters obtained from the Jiles–Atherton hysteresis model : The 40th annual conference on magnetism and magnetic materials (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 6470-6472 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The Jiles–Atherton theory is based on considerations of the dependence of energy dissipation within a magnetic material resulting from changes in its magnetization. The algorithm based on the theory yields five computed model parameters, MS, a, α, k, and c, which represent the saturation magnetization, the effective domain density, the mean exchange coupling between the effective domains, the flexibility of domain walls and energy-dissipative features in the microstructure, respectively. Model parameters were calculated from the algorithm and linked with the physical attributes of a set of three related melt-quenched permanent magnets based on the Nd2Fe14B composition. Measured magnetic parameters were used as inputs into the model to reproduce the experimental hysteresis curves. The results show that two of the calculated parameters, the saturation magnetization MS and the effective coercivity k, agree well with their directly determined analogs. The calculated a and α parameters provide support for the concept of increased intergranular exchange coupling upon die upsetting, and decreased intergranular exchange coupling with the addition of gallium. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.361975
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  • 4
    Electronic Resource
    Electronic Resource
    Microstructural and magnetic investigations into the origins of high coercivity in die-upset praseodymium–cobalt–carbon based magnets (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 351-360 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Melt-quenched and thermomechanically deformed samples with the nominal compositions Pr18Co82, Pr18Co81C, and Pr18Co76C6 were examined with optical and electron microscopy, differential thermal analysis, and superconducting quantum interference device magnetometry that was performed in the temperature range 20 K≤T≤300 K. At room temperature, Pr18Co82 exhibits poor coercivity and remanence, 600 Oe and 2.9 kG, respectively. Pr18Co81C exhibits relatively superior remanence, 7.7 kG, but poor coercivity, 2.7 kOe, while Pr18Co76C6 exhibits the opposite trend, BR=4.5 kG and Hci=12 kOe. The main phase present in all samples, PrCo5, has basically the same character and morphology for all three samples and shows no evidence of intragranular carbon, which is demonstrated to reside in the impurity phases. The superior coercivity found in Pr18Co76C6 is attributed to a previously unknown triclinic phase, Pr3Co4Cx (x≈3–4) that appears to undergo a magnetic–nonmagnetic transition with increasing temperature around T=80 K. The variety of magnetic properties exhibited by each sample is due to the variety of minor phases present in each sample, which may be a product of the effect that carbon has on the solidification rate of the parent alloy. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.360837
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  • 5
    Electronic Resource
    Electronic Resource
    Characterization of defects in Si and SiO2−Si using positrons (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 4935-4982 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In the past few years, there has been rapid growth in the positron annihilation spectroscopy (PAS) of overlayers, interfaces, and buried regions of semiconductors. There are few other techniques that are as sensitive as PAS to low concentrations of open-volume-type defects. The characteristics of the annihilation gamma rays depend strongly on the local environment of the annihilation sites and are used to probe defect concentrations in a range inaccessible to conventional defect probes, yet which are important in the electrical performance of device structures. We show how PAS can be used as a nondestructive probe to examine defects in technologically important Si-based structures. The discussion will focus on the quality of overlayers, formation and annealing of defects after ion implantation, identification of defect complexes, and evaluation of the distribution of internal electric fields. We describe investigations of the activation energy for the detrapping of hydrogen from SiO2−Si interface trap centers, variations of interface trap density, hole trapping at SiO2−Si interfaces, and radiation damage in SiO2−Si systems. We also briefly summarize the use of PAS in compound semiconductor systems and suggest some future directions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.357207
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  • 6
    Electronic Resource
    Electronic Resource
    SiO2/Si interface probed with a variable-energy positron beam (1987)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 51 (1987), S. 1022-1023 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The annihilation characteristics of a monoenergetic beam of positrons, after implantation in Si with a 350-nm overlayer of SiO2, were measured as a function of mean implantation depth. Positrons implanted overlapping the SiO2/Si interface were observed to decay from a state with properties distinctively different from the state in bulk Si and the thermally grown SiO2, i.e., a positron interface state. The momentum distribution of the annihilating positron-electron pair, as observed in the Doppler broadening of the annihilation line, is much broader for this state than for either bulk Si or SiO2, in contrast to previously observed localized positron states in solids and at surfaces which show a narrower distribution.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.98818
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  • 7
    Electronic Resource
    Electronic Resource
    Crystallographic texture determinations from inverse susceptibility measurements : The 41st annual conference on magnetism and magnetic materials (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 81 (1997), S. 5091-5093 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Determination of the quantitative relationship between crystallographic texture and magnetic properties in advanced permanent magnets may be hampered by complex microstructures, which complicate methods that rely on diffraction, or by interparticulate interactions, which adversely affect methods based on magnetic remanence measurements. To this end, new techniques in the determination of texture of bulk permanent magnets are being explored to overcome these inherent experimental difficulties. The analysis of inverse paramagnetic susceptibility measurements constitutes a new method to investigate crystallographic texture. Such measurements also provide Curie temperature data, which are sensitive to chemical changes that may have occurred in the magnetic phase during processing. The mathematical formalism underlying the analysis of inverse susceptibility measurements is outlined, and is used to evaluate magnetic measurements taken from a series of Nd2Fe14B magnets that have been processed by different means, and thus contain different degrees of texture. While this method does provide qualitative information concerning the relative crystallographic alignment of magnet samples, it needs calibration to obtain an explicit value for a texture order parameter. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.364953
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  • 8
    Electronic Resource
    Electronic Resource
    Die-upset Pr-Fe-B-type magnets from melt-spun ribbons (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 4208-4213 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In order to optimize the magnetic properties of die-upset Pr-Fe-B magnets, we have systematically altered alloy compositions, including partial substitution of cobalt and neodymium, and low-level additions of gallium. In general, the remanences of Pr-Fe-B die-upset magnets were lower by ∼1 kG, and coercivities were higher by ∼4 kOe, than analogous Nd-Fe-B magnets. The microstructure of the Pr-Fe-B die-upset magnets was similar to Nd-Fe-B magnets. Both systems are two phase, consisting of oriented flat platelet-shaped grains of 2-14-1 separated by a rare earth-rich intergranular phase. The intergranular phase is thicker for the Pr-Fe-B magnets, resulting in enhanced magnetic domain wall pinning and increased coercivity. Even higher coercivities were obtained with small amounts of cobalt substitution (≤5 at. % of the transition metal) and by very low-level additions of gallium (≤0.5 at. %). The largest remanence (Br=13.7 kG) for a Pr-based 75% die-upset magnet was obtained with the alloy (R13TM81B6)0.9975Ga0.25, where R=(Pr0.8Nd0.2) and TM=(Fe0.95Co0.05).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.356006
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  • 9
    Electronic Resource
    Electronic Resource
    Low-energy contributions to positron implantation (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 3479-3496 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A detailed knowledge of low-energy positron implantation is of considerable importance for depth profiling and data analysis in slow positron experiments. Existing Monte Carlo models are capable of simulating the behavior of positrons incident at keV energies, then following the energy-loss process to final kinetic energies of from 20 to 100 eV. A Monte Carlo calculation of the final stages of positron thermalization in Al, Cu, and Au, from 25 eV to thermal energies, is described via the mechanisms of conduction-electron and longitudinal acoustic-phonon scattering. This calculation produces a wide variety of data, including implantation profiles, fraction and energy distribution of reemitted positrons, and the mean thermalization time. A way to obtain information about positron energy loss by considering the time evolution of a point concentration (delta-function distribution) of positrons is described. Diffusion coefficients are obtained that are in good agreement with experiment. The effects of a positive positron work function are examined in the context of a positron Monte Carlo calculation. It is shown that the latter stages of thermalization can have important effects on the stopping profiles and mean depth. In particular, calculated stopping profiles and mean implantation depth are not adequately described by the Makhovian distribution, in agreement with recent experimental findings. A parameterization of these profiles is provided which will be of use in the analysis of experimental data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.355282
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  • 10
    Electronic Resource
    Electronic Resource
    Alternating current losses in stacked Bi2Sr2Ca2Cu3O10/Ag tapes in perpendicular magnetic fields (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 88 (2000), S. 2709-2717 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Alternating current losses in stacks of powder-in-tube-processed Bi2Sr2Ca2Cu3O10/Ag tapes were measured in perpendicular magnetic fields and compared with calculated hysteresis losses based on the critical-state model. Four main factors had to be taken into account for the calculations of the losses: (1) the inclusion of the area of the Ag sheath in determining the critical-current densities of the stacks, (2) the zero-applied-field critical currents Ic⊥(0) with truly perpendicular fields only, not the standard self-field critical current IcS(0), and (3) the field-dependent critical current Ic(H), e.g., the Kim's model, and (4) the subtraction of the frequency-dependent losses at very high fields. With these considerations, the agreement between the calculated and the measured values of the losses is excellent for fields beyond the full-penetration fields. However, these factors did not totally account for the low-field losses. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1287408
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