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  • 1
    Electronic Resource
    Electronic Resource
    High frequency relaxation of o-terphenyl (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 4632-4636 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Results of molecular dynamics simulations (MDS) of o-terphenyl, a glass-forming liquid, are analyzed in terms of the coupling model of relaxation. At low temperatures thermally activated relaxation processes are suppressed, whereby the density–density correlation function, C(t), obtained by MDS is determined entirely by vibrational modes. This enables the low temperature data to be used to deduce the vibrational density of states, g(ω). With g(ω) determined, the vibrational contribution, Cpho(t), is calculated at higher temperatures assuming that g(ω) is independent of temperature. At higher temperatures, relaxation makes its appearance and is modeled here by the fast dynamics of the coupling model. Assuming that vibration and relaxation contribute independently, the density–density self-correlation function is given by the product Cpho(t)Crel(t), with the relaxation part obtained from the coupling model. There is good overall agreement between the calculated C(t) and the MDS data. Microscopic parameters, including the energy barrier for reorientation of the o-terphenyl molecule, are extracted from the MDS results. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.470651
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  • 2
    Electronic Resource
    Electronic Resource
    Metal-metal versus anion-anion bonding in B31 structures : 37th Annual conference on magnetism and magnetic materials (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 5704-5706 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The evolution with x in V1−xTixS of the lattice parameters and magnetic susceptibility are contrasted with the situation for CoAs. The V1−xTixS system exhibits metal-metal bonding with a transition from the B81 structure of TiS to the B31 structure of VS as the metal-metal bonding in the basal planes of the B81 structure weakens with increasing vanadium concentration. In the transition region, the loss of up to 7 mol % sulfur stabilizes the B81 versus the B31 phase. The V1−xTixS system is Pauli paramagnetic. In CoAs, on the other hand, a distortion to B31 symmetry is shown to be due to metalloid-metalloid bonding, and the compound exhibits antiferromagnetic long-range order below TN=54 K, but with a weak ferromagnetic component if cooled in a magnetic field.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.353597
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  • 3
    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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  • 4
    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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  • 5
    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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  • 6
    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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  • 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
    High-temperature containerless calorimeter (1985)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 56 (1985), S. 430-436 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A high-temperature (〉 1500 K) containerless calorimeter is described and its usefulness demonstrated. The calorimeter uses the technique of omnidirectional electron bombardment of pendant drops to achieve an isothermal test environment. The small heat input into the sample (i.e., 15–50 W) can be controlled and measured. The apparatus can be used to determine the total hemispherical emissivity, specific heat, heat of fusion, surface tension, and equilibrium melting temperature of small molten drops in the temperature range of 1500 to 3500 K. The total hemispherical emissivity εT and specific heat Cp of pure niobium and two alloys of niobium–germanium have been measured in the temperature range of 1700 to 2400 K. As reported in the literature, εT varied as a function of temperature. However, Cp values for both the pure metal and alloys seem to be independent of temperature. Cp for the liquid alloy phase was also measured and compared to the solid phase.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1138318
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  • 9
    Electronic Resource
    Electronic Resource
    A sample holder design and calibration technique for the quantum design magnetic properties measurement system superconducting quantum interference device magnetometer (1996)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 67 (1996), S. 3537-3542 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Magnetic measurements performed on low-susceptibility materials often generate concern for the contribution of the sample holder's moment to the resultant measurement value. In this article, we present a unique design of a sample holder and accompanying calibration technique used to obtain accurate magnetic-moment values from compact, low-susceptibility samples measured with the quantum design magnetic properties measurement system superconducting quantum interference device (SQUID) magnetometer. The sample holder design is simple, highly symmetric, easily fabricated, useful over the full temperature range of the magnetometer and is amenable to a correction algorithm that allows the experimentalist to determine accurately the contribution of the sample holder to the measured value. The sample holder is modeled as a semi-infinite linear density of dipoles, and the response of the internal SQUID coil sections to these dipoles is summed to represent the system response to the sample holder. When the correction algorithm was applied to a measurement of NIST SRM 763 aluminum mounted in the sample holder, the error in the magnetic susceptibility decreases substantially from 41.9% down to 1.1%. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1147172
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  • 10
    Electronic Resource
    Electronic Resource
    Magnetic signature of compositional gradient in exchange-spring bilayer films of CoPt/Co (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 7528-7530 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Experimental studies were performed on model bilayers of fully ordered L10 CoPt with thicknesses of 25, 50, or 100 nm, capped by Co of varying thicknesses from 2.6–75 nm. The bilayers were subjected to different annealing conditions; transmission electron microscopy and x-ray diffraction supplied data concerning the crystallographic structure, microstructure, and texture of the constituent phases in the bilayers. The degree of exchange coupling was investigated primarily with magnetic measurement and magnetic force microscopy. Samples subjected to annealing treatments at 300 °C showed evidence of grain growth and increased texture of the hexagonally close-packed (hcp) cobalt layer relative to the as-deposited condition. The degree of exchange coupling in these materials improved only slightly with annealing, as evidenced by both magnetic recoil curve measurement and magnetic force microscopy. Samples subjected to a higher-temperature annealing treatment of 550 °C evidenced dramatic improvement in the magnetic coupling, an improvement attributed to interdiffusion of CoPt and Co and the formation of alloy phases, specifically face-centered-cubic and hcp Co–Pt solid solutions. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1354594
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