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  • Electronic Resource  (47)
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  • 1
    Electronic Resource
    Electronic Resource
    Magnetic ordering of Pr in Pb2Sr2PrCu3O8 : 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. 7124-7126 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The magnetic ordering of the Pr ions in Pb2Sr2PrCu3O8 has been studied using neutron-diffraction and ac-suspectibility measurements. An imperfect three-dimensional magnetic ordering of the Pr spins was observed at a temperature well below its Neel temperature of TN≈7 K. The magnetic intensities observed at T=1.4 K can be explained by assuming long-range order in the ab plane with short-range correlations, of correlation length ξc=20 A(ring), along the c axis and a moment directed along the c-axis direction. The magnetic ordering is 2D in nature, and the basic magnetic structure consists of nearest-neighbor spins that are aligned antiparallel along all three crystallographic directions. The magnetic transition is also evident in the ac-susceptibility versus temperature measurements, where a cusp that is typical of antiferromagnetic ordering is clearly observed, which matches the TN obtained by neutron diffraction.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.358051
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  • 2
    Electronic Resource
    Electronic Resource
    Effects of Ga doping on the magnetic ordering of Pr in PrBa2Cu3O7 : 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. 7136-7138 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Neutron-diffraction and ac-susceptibility measurements have been performed to study the effects of Ga doping on the magnetic ordering of the Pr in PrBa2(Cu1−xGax)3O7. The Ga atoms preferentially replace the Cu atoms in the CuO-chain layers, and this substitution is found to decrease the antiferromagnetic ordering temperature as the Ga concentration is increased. In addition, the spin arrangement along the c axis is found to change from nearest neighbors being antiparallel for x=0 to nearest neighbors being parallel for x=0.08 (24% Cu chain substitution); for an intermediate x of 0.04 a mixture of the two spin structures is observed. The susceptibility results exhibit Curie–Weiss behavior above TN, and departures from this behavior in the ordered state.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.358055
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  • 3
    Electronic Resource
    Electronic Resource
    Two-dimensional magnetic order in Pb2Sr2TbCu3O8 : 38th Annual Conference on Magnetism and Magnetic Materials (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 6598-6600 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Neutron diffraction techniques have been used to investigate the magnetic ordering of the Tb ions in polycrystalline Pb2Sr2TbCu3O8. Significant magnetic correlations are found to develop below ∼10 K, and these correlations are two dimensional in nature, representative of the strongly anisotropic magnetic interactions in these layered materials. The correlation length increases with decreasing temperature, and long-range order is observed to develop at TN≈5.5 K. However, the sawtooth Bragg profile for the scattering demonstrates that the long-range order is two dimensional, rather than three dimensional, with a spin configuration where nearest-neighbor spins are antiparallel. The scattering profile can be explained quantitatively by assuming long-range order within the ab plane, with no significant correlations along the c axis to the lowest temperatures measured (1.36 K). Our results suggest that the system is well described by a two-dimensional Ising model. The only other (pure) system where a crossover to three-dimensional behavior is not observed is DyBa2Cu4O8.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.356907
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  • 4
    Electronic Resource
    Electronic Resource
    Magnetic, structural, and spin dynamical properties of La1−xCaxMnO3 : The 41st annual conference on magnetism and magnetic materials (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 81 (1997), S. 5488-5490 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Neutron scattering has been used to study the magnetic order, spin dynamics, and structural properties of La1−xCaxMnO3 in the ferromagnetic regime (0〈x〈〈fraction SHAPE="CASE"〉12). For x=〈fraction SHAPE="CASE"〉13(TC=250 K) where the magnetoresistance effects are largest the system behaves as an ideal isotropic ferromagnet at low T, with a gapless (〈0.04 meV) dispersion relation E=Dq2 and DT=0(approximate)155 meV Å2. However, an anomalous diffusive component develops above ∼200 K and dominates the fluctuation spectrum as T→TC. A magnetic field strongly reduces this quasielastic scattering, shifting the spectral weight into the spin wave component of the fluctuation spectrum. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.364576
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  • 5
    Electronic Resource
    Electronic Resource
    The Néel temperature of nanocrystalline chromium (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 1364-1366 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Wide-angle neutron diffraction measurements taken at temperatures from 6 to 250 K indicate that the portion of a chromium sample with a mean grain size of 73 nm is antiferromagnetically ordered at temperatures below 100 K. The Néel temperature (about 120±10 K) for this nanocrystalline sample is suppressed considerably below that of strain-free single-crystal chromium (311 K). © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.360765
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  • 6
    Electronic Resource
    Electronic Resource
    Temperature dependence of the magnetic excitations in ordered and disordered Fe72Pt28 : 38th Annual Conference on Magnetism and Magnetic Materials (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 6072-6074 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have performed inelastic neutron scattering measurements of the long-wavelength spin wave excitations of both ordered and disordered Fe72Pt28 single crystals below their critical temperatures, TC=510 and 375 K, respectively. The spin waves followed the expected E=Dq2 dependence, and the temperature-dependent spin stiffness D decreased as (T/TC)5/2, as expected for an isotropic ferromagnet. The extrapolated zero-temperature spin stiffness was D=98(4) meV A(ring)2 and 107(1) meV A(ring)2 for the disordered and ordered alloy, respectively. These values are significantly higher than the zero-temperature stiffness as determined by magnetization measurements.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.355461
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  • 7
    Electronic Resource
    Electronic Resource
    Neutron scattering studies of the magnetic order in RNi2B2C : The 40th annual conference on magnetism and magnetic materials (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 5857-5859 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Neutron diffraction has been used to investigate the magnetic order of RNi2B2C. For R=Er the system orders antiferromagnetically at TN=6.8 K, and this long range order coexists with superconductivity (Tc=11 K). The magnetic structure is an incommensurate, transversely polarized spin-density-wave state, with the modulation wave vector δ along the a axis and the moments along b. δ has a temperature-independent value of 0.5526 (2π/a), with the structure squaring up at low temperatures. For R=Ho the moments also prefer to reside in the a–b plane, but initially an incommensurate c-axis spiral state forms upon cooling, with TN≈TC≈8 K. This c-axis spiral consists of ferromagnetic sheets of holmium moments in the a–b plane, but with each sheet rotated by ∼163° as one proceeds along the c axis. Small a-axis peaks are also observed above the reentrant superconducting transition over a narrow temperature range, but the c-axis peaks dominate. Just below the reentrant transition at ∼5 K the magnetic system locks-in to a simple commensurate antiferromagnetic structure, which permits superconductivity to be restored. The c-axis spiral, the a-axis component, the commensurate antiferromagnetic structure, and the superconducting phase are all in a delicate balance energetically, and this balance may be easily shifted by subtle changes in composition, magnetic field, and pressure. DyNi2B2C orders antiferromagnetically at TN=11 K, with the same commensurate antiferromagnetic structure as found for the holmium material at low temperature. The existence of superconductivity in some samples of DyNi2B2C is consistent with the antiferromagnetic structure observed. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.362150
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  • 8
    Electronic Resource
    Electronic Resource
    Neutron scattering studies of the vortex lattice in niobium and FR 123 superconductors (invited) : 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. 6772-6777 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The magnetic flux lattice undergoes a melting transition not only in high-Tc oxide superconductors, but also in conventional superconductors, as recently observed in superconducting niobium films. Small-angle neutron scattering was used to investigate the properties of the magnetic flux lattice in a large, high-quality single crystal of niobium. The small London penetration depth of niobium gives a large magnetic scattering signal, and the use of a high-quality single crystal eliminates other unwanted scattering (from twin boundaries, voids, etc.). The signal-to-noise ratio is therefore improved by several orders of magnitude over the best available measurements of high-Tc oxide superconductors. A sixfold hexagonal pattern of peaks is observed in the mixed state (Hc1〈H〈Hc2) at all temperatures. These peaks are resolution limited below the irreversibility line; above it, the width in the transverse direction increases with temperature due to the vortex dynamics. Close to Hc2, the radial widths of the peaks also broaden. The increase in broadening is a direct observation of a transition to a disordered phase. Nevertheless, the basic hexagonal pattern of peaks is maintained throughout the mixed state, indicating that a correlated flux fluid exists in the reversible regime. Some results on the vortex lattice in superconducting DyBa2Cu3O7 are presented and some of the possible exotic states resulting from the coexistence of antiferromagnetic order and superconductivity are described.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.358127
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  • 9
    Electronic Resource
    Electronic Resource
    Vortex structures in YBa2Cu3O7 (invited) : 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. 6778-6783 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Extensive small angle neutron scattering experiments have been conducted on the vortex system in YBa2Cu3O7 in a magnetic field range of 0.5 T≤H≤5 T, and with various orientations of the magnetic field with respect to the crystallographic axes. For H parallel to the c axis, the vortex lattice is oblique with two nearly equal lattice constants and an angle of 73° between primitive vectors. One principal axis of the vortex lattice coincides with the (110) direction of the crystal lattice. It is shown that this structure cannot be explained in the framework of a purely electrodynamic (London) model, and that it is intimately related to the in-plane anisotropy of the superconducting coherence length. When the field is inclined with respect to the c axis, the uniaxial anisotropy due to the layered crystal structure of YBa2Cu3O7 becomes relevant. The interplay between the square in-plane anisotropy and the uniaxial anisotropy leads to both a continous structural transition and a reorientation of the vortex lattice as a function of inclination angle. For the largest inclination angles, the vortex lattice decomposes into independent chains.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.358531
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  • 10
    Electronic Resource
    Electronic Resource
    Neutron scattering investigation of the structure and spin dynamics in La0.85Sr0.15MnO3 : The 41st annual conference on magnetism and magnetic materials (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 81 (1997), S. 5491-5493 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have performed diffraction and inelastic neutron scattering experiments on a La0.85Sr0.15MnO3 single crystal. In the ferromagnetic phase of this system (Tc=235 K) the long wavelength dispersion relation along the (0,1,0) direction is well represented by E=E0+Dq2, but with the spin wave spectrum almost gapless (E0〈0.1 meV), and with DT=0=83.75±0.36 meV Å2. The spin-wave stiffness constant D(T) exhibits a power law behavior as a function of temperature, and appears to collapse as T→Tc. An orthorhombic–rhombohedral structural phase transition is observed at Ts=360 K, and exhibits a hysteretic character suggesting a first-order transformation. Anomalies in magnetization measurements and Bragg peak intensities indicate the existence of a second phase transition at T=200 K. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.364846
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