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  • 1
    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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  • 2
    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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  • 3
    Electronic Resource
    Electronic Resource
    Directional isothermal growth of highly textured Bi2Sr2CaCu2Oy (1993)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 63 (1993), S. 982-984 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: For Bi2Sr2CaCu2Oy (2212), it is shown that an oxygen gradient, as opposed to a temperature gradient, can be used to produce large bulk forms of the 2212 superconductor with highly textured microstructures from an oxygen-deficient melt held at a constant temperature. Material produced in this manner was found to have transition temperatures between 85 and 92 K, high critical current densities below 20 K, and modest critical current densities at 77 K.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.109865
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  • 4
    Electronic Resource
    Electronic Resource
    Mechanism for flux pinning in NdBa2Cu3O7−δ melt-textured in low oxygen partial pressure (1997)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 71 (1997), S. 3572-3574 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: When NdBa2Cu3O7−δ (Nd123) is melt-textured in low oxygen partial pressure (Po2) and subsequently annealed in oxygen to produce the superconducting phase, there is a considerable enhancement of flux pinning compared to Y123. This enhancement is accompanied by a precipitation mechanism due to a change of the solubility limits of Nd1+xBa2−xCu3O7−δ between the high temperature low Po2 conditions used in melt-textured growth and the low temperature oxygen annealing. Transmission electron microscopy reveals a coherent intermediate precipitate structure with a composition of BaCuO2 and a high density of dislocations. We believe these defects are responsible for the strong flux pinning in this material. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.120395
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  • 5
    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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  • 6
    Electronic Resource
    Electronic Resource
    A generalized solidification model and microstructural verification for the Nd–Fe–B–Ti–C system processed by rapid solidification : The 41st annual conference on magnetism and magnetic materials (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 81 (1997), S. 4459-4461 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: For the Nd2Fe14B (2-14-1) compound, the optimal grain size should be smaller than the size of the single domain size of 150 nm. Transition metal carbides (TMC) also reduce the quench rate necessary to achieve the optimal or overquenched condition. This allows inert gas atomization (IGA) to produce viable magnetic materials. In this article we will demonstrate that optimal microstructure for the 2-14-1 can be produced by IGA with the addition of TiC. Moreover, a solidification model will be presented to show (1) how recalescence is a critical feature to the evolution of the microstructure in rapidly solidified materials and (2) the role TMC and other solute phases have on inhibiting grain growth so that lower quench rates can be employed. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.364975
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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
    Specific Heat of YBa2Cu3O7−−δ and (La2−xSrx)CuO4: Evidence for d-Wave Pairing (1999)
    Springer
    Journal of superconductivity 12 (1999), S. 105-111 
    Details
    ISSN: 1572-9605
    Keywords: Specific heat ; YBCO ; LSCO ; d-wave
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract New low-temperature specific-heat data for YBa2Cu3O7−δ, 0≤δ≤0.2, and (La1.85Sr0.15)CuO4 in magnetic fields (H) to 9 T are reported. They show features predicted for the lines of nodes in the energy gap that are expected for d-wave pairing; for H=0, a T 2 term; for H≠0 an H 1/2 T term with a crossover to a more complicated T dependence at higher T and lower H. The results are compared with recent measurements in other laboratories.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1007790107549
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