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  • 1
    Electronic Resource
    Electronic Resource
    Effect of milling on the magnetic and microstructural properties of Sm2Fe17Nx permanent magnets : 38th Annual Conference on Magnetism and Magnetic Materials (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 6018-6020 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: By ball milling Sm2Fe17Nx the coercivity can be increased from 0.3 to 1.5 T. The coercivity increases continuously during milling up to a time of about 600 min, and then decreases for too intensive ball milling. This is connected to particle size reduction and other effects like the increase in oxygen content, introduction of mechanical stresses, formation of new grain boundaries, and amorphization of the material. Magnetic measurements, scanning electron microscopy, as well as domain wall observations indicate that long-time milled material is mainly constituted of single domain particles and isotropic polycrystalline particles with small grains.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.355494
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  • 2
    Electronic Resource
    Electronic Resource
    Comparison of magnetic methods for the determination of texture of permanent 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. 6268-6270 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The singular point detection (SPD) technique as well as a least-mean-square procedure of fitting trial texture functions to demagnetization curves (DMC) were applied in order to determine the orientation density of the tetragonal axes of the Nd2Fe14B crystallites in sintered Nd-Fe-B magnets with different degrees of grain alignment. Both methods are less complicated than calculating the texture function from x-ray-diffraction data. The orientation densities obtained by both methods agree fairly. Analytically, they can be described as a Gaussian or a sum of cosine-power functions of the angle between the local tetragonal axis and the texture axis. This agreement is a test for the DMC method which can also be used for materials showing much larger anisotropy fields than the maximum available measuring field. The SPD and DMC methods can also be applied to measure the temperature dependence of the anisotropy field HA of the magnetic main phase in noncompletely textured polycrystalline materials. By means of the DMC method additionally the spontaneous polarization Js as well as the anisotropy constants K1 and K2 can be determined. As expected, the values of HA of our sintered Nd-Fe-B samples, measured up to 140 °C, are nearly independent of the degree of texture and are in agreement with those reported in literature. This confirms that SPD as well as DMC can be used to measure intrinsic magnetic properties for materials which can hardly be prepared as single crystals, such as interstitial compounds made by gas–solid reactions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.358301
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  • 3
    Electronic Resource
    Electronic Resource
    Kerr microscopy observation of carbon diffusion profiles in Sm2Fe17Cx : 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. 6717-6719 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effect of carbon diffusion from CH4 gas into coarse Sm2Fe17 powder on the magnetic domain structure (MDS) was studied at room temperature by means of the magneto-optical polar Kerr effect. The diffusion occurs initially along preferential paths and then through the bulk. A gradual variation in the MDS through incompletely carburized grains was observed, which reflects local changes in spontaneous magnetization and magnetic anisotropy. This suggests the existence of smooth "bathtublike'' carbon concentration profiles. An acceleration of the carburization process caused by cracking of grains during the diffusion was observed. The diffusivity R of carbon in Sm2Fe17 at 450 °C was estimated to be 2.5×10−16 m2/s. For Sm2Fe17C2.2 the domain-wall energy density is γ=3.1×10−2 J/m2, the domain-wall thickness δ=3.3 nm, the single-domain particle size Dc≈0.3 μm, and the exchange constant A=8.1×10−12 J/m.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.358177
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  • 4
    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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  • 5
    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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  • 6
    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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  • 7
    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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  • 8
    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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  • 9
    Electronic Resource
    Electronic Resource
    Investigation of the expanding plasma of an anodic vacuum arc (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 3625-3629 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An aluminum plasma is produced by an anodic vacuum arc (25 A, 17 V) with a consumable anode. The plasma expands from the anode to the walls and is investigated by Langmuir probes, a quadrupole mass spectrometer, a retarding field ion energy analyzer, and a quartz-crystal oscillator for mass flow detection. The electron density ranges within 2×1015–3×1017 m−3 and the electron temperature within 0.4–0.9 eV. At a target, ion fluxes of 1.5×1019–8×1020 m−2 s−1 and total particle fluxes of 3×1020–4×1021 m−2 s−1 are measured. The ions are accelerated in the expanding plasma towards the target and gain a few eV. By a simple collisionless transport model of the expanding plasma, the plasma potential and floating potential are calculated and compared with experimental data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.345315
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  • 10
    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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