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  • 1
    Electronic Resource
    Electronic Resource
    Reinvestigation of the thiourea-cyclohexane inclusion compound by deuterium NMR spectroscopy (1991)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 95 (1991), S. 407-413 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100154a071
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  • 2
    Electronic Resource
    Electronic Resource
    On the role of Zn in Sm2Fe17Nx permanent magnets : 37th Annual conference on magnetism and magnetic materials (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 6044-6046 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Coercivities up to 1.9 T were achieved by bonding micron-size Sm2Fe17Nx particles with zinc. X-ray analysis of Zn-bonded samples indicates the presence of the ZnFe Γ phase and no unreacted Zn, after heat treatment at about 390 °C for 100 min for samples with Zn content varying from 5 to 35 wt. %. The increase of coercivity occurs only for a more intense heat treatment, e.g., at 390 °C for 300 min or 425 °C for 100 min. Differential scanning calorimetry (DSC) shows two exothermic peaks at 388 and 426 °C, but no endothermic peak related to the melting of Zn (at 419.6 °C) was observed. In dilatometric measurements two peaks were observed for the rate of length change near the same temperatures as the DSC peaks. Polarization-versus-field curves point to an additional ferromagnetic phase with (i) a Curie temperature near 180 K and (ii) 2% of the net magnetization at low temperatures. The corresponding dip in low-temperature demagnetization curves, however, is about 10% in depth. Most of the Sm2Fe17Nx grains in the demagnetized Zn-bonded magnets are multidomain. We found γ≈3.4×10−2 J/m2 and Dc≈0.3 μm for the wall energy and for the critical single-domain particle diameter, respectively.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.353464
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  • 3
    Electronic Resource
    Electronic Resource
    Spatiotemporal evolution of a low-pressure glow discharge (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 6694-6699 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The spatiotemporal evolution of a pulsed low-pressure glow discharge is investigated theoretically and experimentally. The discharge is modelled phenomenologically by a reaction-diffusion equation in which the cathode fall and the negative glow of the discharge are described as a bistable layer. A laterally one-dimensional discharge is realized experimentally by a hollow cathode discharge in a slotted cathode. With the help of probe measurements, a homogeneous evolution with a laterally uniform current rise and an inhomogeneous evolution starting from special sites and progressing along the cathode are found. The main experimental results are reproduced by model calculations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.349843
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  • 4
    Electronic Resource
    Electronic Resource
    Magnetic reversal in Sm2Fe17Ny permanent magnets : 37th Annual conference on magnetism and magnetic materials (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 6047-6049 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Coercivity and nucleation fields for three-dimensional inhomogenities are calculated and discussed. For soft spherical inclusions in a hard magnetic matrix a (δ/R)2 dependence of the nucleation field on inclusion radius R and domain wall width δ has been obtained. To calculate propagation fields for spherical inhomogenities, a nonlinear model has been used. The corresponding coercive field can be much higher than the nucleation field, particularly if the magnitude of the anisotropy changes very steeply. Soft inclusions with sharp interfaces are ineffective at producing complete magnetic reversal. For partly nitrided particles coercivity and nucleation field are predicted to be identical, which is confirmed by experiments on high-performance Sm2Fe17N3−δ magnets.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.353465
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  • 5
    Electronic Resource
    Electronic Resource
    Sample size dependence of the critical current density in polycrystalline YBa2Cu3O7−δ (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 2964-2968 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The zero-field transport critical current density 〈Jc〉 of polycrystalline YBa2Cu3O7−δ has been measured at 77 K for slabs of different thickness d. It was found that 〈Jc〉 increases as the thickness decreases. The experimental data is in agreement with a field-dependent Jc(H) that decreases with increasing field. However, a clear distinction between a Kim, exponential, and power law model cannot be made.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.351501
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  • 6
    Electronic Resource
    Electronic Resource
    Proton spin-lattice relaxation dispersion of liquid crystal polymers: Characterization of local and collective motions (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 3794-3802 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: This paper reports on studies of the longitudinal proton spin relaxation dispersion T1Z(ω) of a nematic main chain liquid crystal polymer (M¯n=30 000) over a very broad Larmor frequency range (1 kHz≤ω/2π≤120 MHz). Analysis of the experiments is achieved in terms of a density operator treatment employing the Redfield approximation. The results show that collective motions contribute to the proton spin relaxation process in the kilohertz regime, as found for low molar mass liquid crystals, whereas the conventional megahertz range is dominated by reorientation of individual molecules. The intramolecular motions consist of trans–gauche isomerization and phenyl ring flips. These motions are the fastest in the hierarchy of time with correlation times of 10−10 s in the nematic melt of the polymer at T≈460 K. The intermolecular (whole molecule) motions are interpreted as rotational diffusion in an orienting potential. They exhibit a T1Z(ω)∼ω0.65 dispersion in the megahertz range and have correlation times ranging from 10−9 to 10−7 s at this temperature. The slowest motions affecting longitudinal spin relaxation can be assigned to nematic order director fluctuations characterized by a broad distribution of thermally activated modes. Analysis of the dispersion profiles in the kilohertz regime provides the viscoelastic parameters of the main chain liquid crystal polymer. At T=460 K, an average elastic constant of K=8×10−11 N and an effective viscosity of η=1×103 Pa s have been determined. Using the experimentally accessible value for the short wavelength cutoff of the elastic modes, one obtains the mean-square amplitude of the director fluctuations 〈θ02(approximately-greater-than)=0.02, corresponding to a director order parameter of SOF=0.98. Thus, the contributions of the collective chain motions to the measured order parameters are negligible.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.462960
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  • 7
    Electronic Resource
    Electronic Resource
    Highly coercive SmCo5 magnets prepared by a modified hydrogenation-disproportionation-desorption-recombination process (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 5666-5668 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The hydrogenation-disproportionation-desorption-recombination (HDDR) process was applied to SmCo5 using extreme conditions, namely high hydrogen pressures and reactive milling under hydrogen. Investigations on the hydrogen absorption behavior of SmCo5 by differential scanning calorimetry under hydrogen pressures between 1 and 7 MPa showed absorption events due to an interstitial absorption at about 100 °C and a disproportionation reaction at about 600 °C. X-ray diffraction showed the disproportionation of SmCo5 into Sm hydride and fcc-Co. A favorable effect of high hydrogen pressures on the disproportionation reaction was observed which can be explained by a decrease of the free enthalpy of the samarium hydride for increasing hydrogen pressures. Reactively milled SmCo5 showed also the products of the disproportionation reaction. The recombination to the original SmCo5 phase on hydrogen desorption in a subsequent heat treatment in vacuum was successful for both methods. However, Sm2O3, Sm2Co17, and Sm2Co7 were detected as minor phases. Maximum coercivities μ0JHC of 2.1 and 4.7 T were achieved for high pressure and reactively milled HDDR powders, respectively. The high coercivities originate from the high anisotropy field of the SmCo5 phase in combination with the grain refinement due to the HDDR treatment. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.369834
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  • 8
    Electronic Resource
    Electronic Resource
    NMR probe for dynamic-angle spinning (1991)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 62 (1991), S. 1445-1452 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We describe the design of a probe for dynamic-angle spinning (DAS) NMR experiments, comprised of a spinning cylindrical sample holder whose axis may be reoriented rapidly between discrete directions within the bore of a superconducting magnet. This allows the refocusing of nuclear spin magnetization that evolves under anisotropic interactions such as chemical shift anisotropy and quadrupolar coupling, providing high resolution NMR spectra for quadrupolar nuclei in solid materials. The probe includes an axial air delivery system to bearing and drive jets which support and spin a rotor containing the sample. Axis reorientation is accomplished with a pulley attached to the probehead and coupled to a stepping motor outside of the magnet. The choice of motor and gear ratio is based on an analysis of the moments of inertia of the motor and load, the desired angular resolution, and simplicity of design. Control of angular accuracy and precision are discussed, as well as the efficiency of radiofrequency irradiation and detection. High resolution DAS spectra of oxygen-17 and aluminum-27 nuclei in polycrystalline minerals illustrate the experimental capabilities.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1142465
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  • 9
    Electronic Resource
    Electronic Resource
    Magnetoresistance of polycrystalline layered manganites La2−2xSr1+2xMn2O7 (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 5420-5422 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Polycrystalline bulk samples of the layered manganites La2−2xSr1+2xMn2O7 showing a colossal magnetoresistance (CMR) effect were prepared for doping levels of x=0.4 and 0.5 by a solid-state reaction route. Temperature and field dependences of magnetization and of electrical resistivity have been measured between 5 K and room temperature. Ferromagnetic behavior with a Curie temperature of TC=135 K and a high value of spontaneous magnetization (64 emu g−1) was found for x=0.4. The x=0.5 compound orders antiferromagnetically near TN=215 K, showing a resistivity enhancement there. The resistivity of the x=0.4 compound shows a field dependence at low temperatures similar to that found for polycrystalline La0.7Sr0.3MnO3. The resemblance includes the presence of both a low-field and a high-field contribution to the magnetoresistance, as well as the magnitude of the low-field MR (−23% at 20 K and −15% at 77 K for H=1 kOe). The low-field MR is attributed to the effect of grain boundaries. In contrast to the grain-boundary MR of La0.7Sr0.3MnO3, it was also observed at temperatures far above the TC of the layered manganite. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.369962
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  • 10
    Electronic Resource
    Electronic Resource
    Sm2Fe17 interstitial magnets (invited) : The 40th annual conference on magnetism and magnetic materials (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 5045-5050 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Various processing routes for making permanent magnets based on interstitially modified Sm2Fe17 have been recently developed. Zn bonding of coarse grained Sm2Fe17N3 gives coercivities μ0JHc as high as 2.2 T. Effective methods to prepare highly coercive Sm2Fe17N3 powders for polymer bonding are mechanical alloying and rapid quenching. With the very simple method of additional milling of coarse grained nitrided powders we achieved μ0JHc≈1.5 T. A coercivity up to 3.5 T has been achieved by a modified HDDR procedure, reducing the particle size of the starting material by milling prior to the hydrogenation–disproportionation–desorption–recombination (HDDR) treatment. This is attributed to a better control of two critical parameters, namely grain size and the amount of unrecombined α-Fe accompanying the intermediate TbCu7 structure-type phase. Resin bonded HDDR-Sm2Fe17N3 magnets show an unexpected high initial susceptibility. This may be due to a strong magnetic interaction of the grains. To develop coercivity in Sm2Fe17Cy(approximately-greater-than)1 obtained by gas–solid reactions of Sm2Fe17 the same methods as those applied to Sm2Fe17N3 can be successfully used. Fully dense magnets with a coercivity up to 1.5 T were made from the interstitially as well as substitutionally modified compound Sm2Fe15Ga2C2 by hot pressing of highly coercive powders. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.361568
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