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  • 1
    Electronic Resource
    Electronic Resource
    New high temperature furnace for structure refinement by powder diffraction in controlled atmospheres using synchrotron radiation (1999)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 70 (1999), S. 3554-3561 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A low thermal gradient furnace design is described which utilizes Debye–Scherrer geometry for performing high temperature x-ray powder diffraction with synchrotron radiation at medium and high energies (35–100 keV). The furnace has a maximum operating temperature of 1800 K with a variety of atmospheres including oxidizing, inert, and reducing. The capability for sample rotation, to ensure powder averaging, has been built into the design without compromising thermal stability or atmosphere control. The ability to perform high-resolution Rietveld refinement on data obtained at high temperatures has been demonstrated, and data collected on standard Al2O3 powder is presented. Time-resolved data on the orthorhombic to rhombohedral solid state phase transformation of SrCO3 is demonstrated using image plates. Rietveld refinable spectra, collected in as little as 8 s, opens the possibility of performing time-resolved structural refinements of phase transformations. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1149948
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  • 2
    Electronic Resource
    Electronic Resource
    An electron channeling study of polycrystalline YBa2Cu3Ox (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 761-765 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An electron channeling study has been done on large grained YBa2Cu3Ox samples. Selected area channeling patterns (SACP) were used to examine several dozen grains on electropolished surfaces and it was demonstrated that (a) the twin planes observed in polarized optical light microscopy lie parallel to {110} crystal planes, and (b) the long flat sides of high aspect ratio grains are formed by basal planes, and the shorter sides are formed by either (010), (100), or {110} planes. A majority of the large grains examined were found to contain subgrains, misaligned by 0.5°–1° and ranging in size from less than 3 to 20 μm. The origin of the subgrains is not understood.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.341921
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  • 3
    Electronic Resource
    Electronic Resource
    A metallurgical approach toward alloying in rare earth permanent magnet systems (abstract) : The 40th annual conference on magnetism and magnetic materials (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 4847-4847 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In bulk permanent magnets, the extrinsic properties relating to the microstructure determined the level of hard magnetic properties that is actually achieved. Many researchers have worked on the microstructure property relationships in the Nd2Fe14B (2-14-1) system but, in general, the approach has been to analyze the microstructure of materials which have been shown to have good magnetic properties rather than to study the effect of alloy additions on the metallurgical properties of the system. The microstructure which is obtained under a given set of processing conditions is highly dependent on the solidification behavior of the alloy, as well as grain growth phenomena. Alloy additions which effect the solidification behavior of the melt and then form precipitates which pin grain boundaries, and therefore control grain size, should be valuable in producing the uniform microstructure required for good magnetic properties. A number of refractory metal carbides perform both of these functions. The carbides have a reasonable degree of solubility in the 2-14-1 melt and, under conditions of reasonable rapid solidification, a degree of metastable solubility in the 2-14-1 phase. However, there is very limited equilibrium solid solubility in the 2-14-1 phase so that the intrinsic magnetic properties are not effected. The addition of these materials to 2-14-1 results in a factor or three reduction of the quench rate required to produce amorphous material. In addition, the crystallization temperature of the glass is enhanced leading to enhance nucleation and finer grain size during crystallization. Finally refractory metal carbide precipitates decorate the grain boundaries of the crystallized material inhibiting grain growth. Transition metal carbide formation, solid and liquid solubility, effects on solidification, nucleation, and grain growth will be discussed. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.361629
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  • 4
    Electronic Resource
    Electronic Resource
    Dependence of energy dissipation on annealing temperature of melt–spun NdFeB permanent magnet materials : The 40th annual conference on magnetism and magnetic materials (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 5510-5512 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A model of magnetic hysteresis which was developed originally for soft magnetic materials has been applied to melt–spun ribbons of Nd2Fe14B-based material. The crucial ideas in the model description of hysteresis center on a dissipation of energy due to hysteresis which is proportional to the change in magnetization. The Nd2Fe14B material was melt–spun amorphous and then annealed for a period of 24 h at temperatures ranging from 700 to 950 °C. This resulted in different grain sizes, depending on annealing temperature. Consequently the hysteresis curves represent the properties of the material as a function of both annealing temperature and grain size. It was found that the magnetic properties varied systematically with annealing temperature, and hence grain size, as would be expected. When modeling the magnetic properties it was found that the model parameters also varied systematically, in particular, the energy dissipation parameter k was to a first approximation a simple linear function of the annealing temperature and decreased with increasing annealing temperature as a result of grain growth. Therefore, this study revealed a basic relationship between materials processing conditions, microstructure, model parameters, and magnetic properties. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.362294
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  • 5
    Electronic Resource
    Electronic Resource
    Preparation of single crystals of superconducting YBa2Cu3O7−x from CuO melts (1987)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 51 (1987), S. 690-691 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Millimeter size single crystals of superconducting YBa2Cu3O7−x (Tc ∼90 K) were grown by melting a mixture of stoichiometric YBa2Cu3O7−x plus excess CuO at 1150 °C followed by holding at 900 °C for four days. Crystals were in the form of plates with c axis normal to the plate face. Growth of the crystals is believed to be aided by a liquid phase which is present at the holding temperature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.98336
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  • 6
    Electronic Resource
    Electronic Resource
    Effect of TiC additions to the microstructure and magnetic properties of Nd9.5Fe84.5B6 melt-spun ribbons : The 7th joint MMM-intermag conference on magnetism and magnetic materials (1998)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 83 (1998), S. 6631-6633 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Rapidly solidified samples of Nd9.5Fe84.5B6 with and without 3 at. % TiC were prepared by melt spinning and melt extraction and then annealed in vacuum (3×10−6 Torr) at temperatures from 600 to 750 °C. For alloys melt spun under similar conditions, the overquenched state was achieved at wheel speeds 〉10 m/s for the TiC added alloy while 〉20 m/s was necessary without TiC. The overquenched samples contained a smaller fraction of α-Fe in smaller grains than the undercooled samples where Fe dendrites formed near the free surface during solidification. These Fe dendrites were not removed by annealing. In addition, large orientated 2-14-1 grains nucleated on the Fe dendrites. This combination is detrimental to the magnetic properties. The addition of TiC results in improved control of the microstructure over a larger fraction of the ribbon volume enhancing the magnetic properties. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.367929
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  • 7
    Electronic Resource
    Electronic Resource
    Magnetoelastic properties of terfenol composites (abstract) : The 41st annual conference on magnetism and magnetic materials (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 81 (1997), S. 5423-5423 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Recent work was undertaken to identify the possibility of using composite Terfenol, consisting of Tb–Dy–Fe in a nonmagnetic, nonmetallic binder, for magnetoelastic sensor applications in which the material needs to be formed into complex shapes, and in which the high levels of magnetostriction obtained in Tb–Dy–Fe alone are unnecessary. Recent results reported by Sandlund et al.1 have indicated the possible use of such a material in high frequency applications. In this work we have studied the material for low frequency, or even dc applications, in which the material could be used to sense an applied torque. The results showed that these composite materials need magnetic fields of typically 800 kA/m to obtain the magnetostriction levels of 350 ppm reported elsewhere.2 Similar work by Peters3 needed fields of over 1 MA/m to obtain magnetostrictive strains beyond 100 ppm. Such field strengths are impractical for low power devices. From the present work, 38 μm Terfenol powder in an epoxy or polymer binder gave magnetostrictive strains of 120 ppm and above for field strengths of 100 kA/m, which is much more appropriate for small low power sensors. A benchmark sensitivity of 18 μ T/N m for measurement of torque levels over the range ± 10 Nm was set based on the response of nickel which has previously been used in magnetoelastic sensors. In the present composite material axial magnetic induction sensitivities of 32 μ T/Nm and tangential field sensitivities of 12 A/Nm2 (=15 μT/Nm) were obtained, which were 50% better than nickel. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.365561
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  • 8
    Electronic Resource
    Electronic Resource
    Mechanical and high-temperature (920 °C) magnetic field grain alignment of polycrystalline (Ho,Y)Ba2Cu3O7−δ (1989)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 65 (1989), S. 3136-3141 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effects of uniaxial compression, high-temperature (920 °C) heat treatment, and heat treatment plus magnetic field on grain alignment in bulk ceramic pellets of HoBa2Cu3O7−δ and YBa2Cu3O7−δ were studied and separated. Uniaxially cold pressing prereacted powder into pellets at room temperature is found to yield significant grain alignment on the flat end surfaces of the pellets perpendicular to the pressing axis, where the c axes of the grains are parallel to this axis, in agreement with previous reports. A simple method to quantitatively determine the degree of surface grain alignment from the powder x-ray diffraction data from these surfaces is used. These data were augmented by x-ray rocking curve measurements. The degree of alignment of the cold pressed samples was found to increase with increasing pressure up to our pressure limit of 310 MPa. However, bulk magnetization anisotropy measurements on these pellets indicate that the degree of bulk alignment is only about 1/3 to 1/2 that inferred from the above surface measurements, which in turn suggests that the degree of alignment decreases with distance from the flat end surfaces. We find that a pronounced additional surface grain alignment is produced by heat treating the cold-pressed samples at high temperature (920 °C). We also observed a significant influence during the high-temperature annealing of a small (0.7 T) applied magnetic field on the alignment of the surface grains. A model to explain these observations is presented and discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.342710
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  • 9
    Electronic Resource
    Electronic Resource
    High performance isotropic permanent magnet based on Nd-Fe-B (1987)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 61 (1987), S. 3577-3579 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have fabricated a macroscopically isotropic permanent magnet material (Ovonic Hi-RemTM) which significantly exceeds conventionally understood performance limits for a material with saturation magnetization Ms =16 kG. Enhanced magnetic properties, including a remanent magnetization Mr =9–10 kG or more, and a maximum energy product in excess of 20 MGOe, are observed without preferred orientation. This material has been fabricated by rapid solidification of an alloy structurally and compositionally similar to Nd2Fe14B, but which depends on critical alloying additions and process parameters to obtain optimum magnetic performance.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.338706
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  • 10
    Electronic Resource
    Electronic Resource
    Effect of the elastic modulus of the matrix on magnetostrictive strain in composites (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 74 (1999), S. 1159-1161 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effect of the matrix material on the magnetostriction of composites containing highly magnetostrictive particles has been studied. Experimental results showed that the elastic modulus of the matrix is an important factor determining the bulk magnetostriction of the composite. For a series of composites with the same volume fraction of magnetostrictive particles but different matrix materials, the bulk magnetostriction was found to increase systematically with decreasing elastic modulus of the matrix. A model theory for the magnetostriction of such composites has been developed, based on two limiting assumptions: uniform strain or uniform stress inside the composite. The theory was then used to predict the magnetostriction of the entire material from the volume fractions of the components, their elastic moduli and magnetostrictions. These predictions were in agreement with the experimental results. It is concluded that to obtain a high magnetostriction and adequate mechanical properties of a composite, the elastic moduli of the magnetostrictive phase and the matrix should be as close as possible in value. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.123473
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