[en] Neutron diffraction techniques have been used to determine the magnetic structure of Fe in monoclinic α-Li₃Fe₂(PO₄)₃. Rietveld analysis of the room temperature powder diffraction pattern confirms the monoclinic structure of the sample and is in agreement with previous studies. At low temperatures a paramagnetic to antiferromagnetic transition is observed at T_N=30.0 K. Our analysis shows that at T=4 K the two inequivalent Fe sites have antiparallel magnetic moments that are aligned along the a-axis. The average magnetic moment, gS=5.0 μ_B indicates homogeneous Fe³⁺ (S=((5)/(2)))

[en] We have made neutron powder diffraction measurements on ScD/sub 1.8/ at a number of different temperatures up to 1000 ⁰C. From these data, we extract the scandium and deuterium mean-square displacements at each temperature. Contrary to recent magnetic resonance results, we find no signature of what has been called sublattice melting

[en] Neutron-diffraction patterns have been measured for isotopically enriched powder samples of calcite using both steady-state and pulsed-neutron techniques. Greatly enhanced precision over previous work has been achieved for /sup 40/Ca and /sup 44/Ca, while the results for /sup 42/Ca, /sup 43/Ca, and /sup 48/Ca represent new data. The coherent scattering lengths deduced from these measurements have been employed in a more definitive analysis of primary electric-dipole gamma rays from thermal-neutron capture. In three cases (/sup 40/Ca, /sup 42/Ca, and /sup 48/Ca) the estimates from a spherical optical-model formulation of the direct-capture mechanism are in agreement with the experimental cross sections. In /sup 44/Ca the theory overestimates the measured cross sections on average by about 60%; this divergence can be explained by considering the modifications to the theory due to collective vibrations of the /sup 44/Ca core

[en] We report on magnetic and structural neutron-diffraction studies of single-crystal La₂CuO_4+x versus temperature. The low-temperature diffraction data are consistent with the coexistence of two structurally related phases: nearly stoichiometric, antiferromagnetic (AF) domains, with average domain diameter ∼500 A in the CuO₂ plane, and oxygen-rich, metallic, and superconducting domains. The ordered magnetic moment in the AF domains does not saturate at 10 K, and is on average, μ=(0.3±0.05)μ_B/Cu atom. The phase-separation transition to these two phases occurs at T_PS=260±5 K, which is about 15 K higher than the Neel temperature, T_N=245±3 K. The value of T_PS is identical within the errors with that (259±2 K) found previously from specific-heat measurements on the same crystal. The structural properties of the single crystal are discussed and compared to those of polycrystalline oxygen-rich La₂CuO_4+x

[en] Neutron-scattering measurements have been performed on the S= (1) /(2) quasi-one-dimensional system Sr_14-xY_xCu₂₄O₄₁, which has both simple chains and two-leg ladders of copper ions. We observed that when a small amount of yttrium is substituted for strontium, which is expected to reduce the number of holes, the dimerized state and the structure in the chain are changed drastically. The inelastic peaks originating from the dimerized state of the chain become broader in energy but not in momentum space. This implies that the dimerized state becomes unstable but the spin correlations are unchanged with yttrium substitution. Furthermore, it was observed that nuclear-Bragg-peak intensities originating from the chain show strong temperature and x dependence, which suggests that the chains slide along the c axis as temperature and x are varied. copyright 1997 The American Physical Society

[en] We present neutron diffraction, magnetic susceptibility and specific heat data for a single-crystal sample of the cubic (Cu₃Au structure) compound Pr₃In. Antiferromagnetic order occurs below T_N=12 K with propagation vector (0,0,0.5±δ) where δ≅1/12. The neutron diffraction results can be approximated with a model where the moments in each of the three Pr sublattices form ferromagnetic sheets perpendicular to and alternating in sign along the propagation direction, with a 12-unit-cell square-wave modulation. The very small specific heat anomaly that we observe at T_N=12 K may be a consequence of the fact that the ordered moment is induced in the Γ₁ singlet when T< T_N. The magnetic susceptibility indicates that in addition to the antiferromagnetic transition at 12 K, there may be a transition near 70 K below which there is a very small remnant magnetization (0.005μ_B)

[en] We report neutron di raction studies of TbCo₂Zn₂0 and TbFe₂Zn₂0, two isostructural compounds which exhibit dramatically different magnetic behavior. In the case of TbCo₂Zn₂0, magnetic Bragg peaks corresponding to antiferromagnetic order are observed below TN 2.5 K with a propagation vector of (0.5 0.5 0.5). On the other hand, TbFe₂Zn₂0 undergoes a ferromagnetic transition at temperatures as high as 66 K which shows a high sensitivity to sample-to-sample variations. Two samples of TbFe₂Zn₂0 with the same nominal compositions but with substantially different magnetic ordering temperatures (Tc 51 and 66 K) were measured by single crystal neutron diffraction. Structural refinements of the neutron difraction data nd no direct signature of atomic site disorder between the two TbFe₂Zn₂0 samples except for subtle differences in the anisotropic thermal parameters. The differences in the anisotropic thermal parameters between the two samples is likely due to very small amounts of disorder. This provides further evidence for the extreme sensitivity of the magnetic properties of TbFe₂Zn₂0 to small sample variations, even small amounts of disorder.

[en] We report the results of a neutron diffraction study, carried out on both single crystalline and polycrystalline samples of Tb₅Si_2.2Ge_1.8 and polycrystalline Tb₅Si_2.5Ge_1.5. On cooling, at approximately 120 K, the Tb₅Si_2.2Ge_1.8 system undergoes a magnetoelastic transition from a high-temperature monoclinic-paramagnetic to a low-temperature orthorhombic-ferromagnetic structure. Between 120 K and 75 K, the magnetic structure has a net ferromagnetic component along the a axis direction. The moments are slightly canted with respect to the a axis, while the components along the b and c axes are ordered antiferromagnetically. A second magnetic transition occurs at approximately 75 K. Below this temperature, the magnetic structure consists of ferromagnetically aligned μ_x and μ_z projections of the magnetic moments and an antiferromagnetic arrangement of the μ_y moment components. Magnetic structures of Tb₅Si_2.5Ge_1.5 are nearly identical to those of Tb₅Si_2.2Ge_1.8

[en] We have studied the lattice dynamics of a Ni₅₄Mn₂₃Al₂₃ (at.%) Heusler single-crystalline alloy by means of neutron scattering and ultrasonic techniques. Results show the existence of a number of precursor phenomena. We have found an anomaly (dip) in the low TA₂ phonon branch at the wave number ξ₀∼0.33 (in reciprocal lattice units) that becomes more pronounced (phonon softening) with decreasing temperature. We have also observed softening of the associated shear elastic constant (C^') with decreasing temperature. Ultrasonic measurements under applied magnetic field, both isothermally and varying the temperature show that the values of elastic constants depend on magnetic order thus evidencing magnetoelastic coupling

[en] The phase diagram of the title system is remarkably rich, exhibiting regions of long-range antiferromagnetic order, short-range (spin-glass-like) order, high temperature superconductivity, or none of these. Here, the phase diagram is reviewed, with an emphasis on our recent studies using ¹³⁹La NQR, powder and single crystal neutron diffraction, and magnetization measurements for 0≤qslantx≤qslant0.15 and 0≤qslantδ< or ∼0.1. ((orig.))