By exciting diffraction in the Laue geometry by specularly reflected beams, penetrating x-rays and neutrons can be used to probe surface and interfacial atomic structure. We present the first such measurement utilizing polarized neutrons with both incident- and exit-angle resolution. We have observed the evolution of magnetic order by monitoring the in-plane (1010) Bragg peak from an epitaxially grown film consisting of 150 Å Y(0001) on 5000 Å Gd(0001). Magnetic scattering increases as the film is cooled from the Gd bulk Curie temperature (293K) to 100 K. The gross features of the data can be captured by a simple two-layer model, but sufficient disagreement remains that one may yet hope to extract non-trivial structure at the Y/Gd interface.

Sputtered Ni80Fe20/Ag multilayers, annealed post-growth, show giant magnetoresistive (GMR) effects at unusually low magnetic fields (≈ 5 Oe)[l]. Structural characterization by cross-sectional TEM[2] and x-ray diffraction indicates that the Ag preferentially diffuses into the Ni80Fe20 layers at the interfaces. Using polarized-neutron specular reflectivity, we have obtained magnetization depth profiles for a series of annealed [Ni8oFe2o(20Å)/Ag(40Å)]4 multilayers. Though GMR in related materials is associated with coherent antiferromagnetic alignment of the ferromagnetic layers, specular neutron data for the Ni80Fe20/Ag multilayers show no trace of half-order spin-flip intensity characteristic of this simple structure. In small applied fields, transverse scans at the half-order position show a broad feature which disappears upon saturation. These data suggest that while the Ni80Fe20 moments are antiferromagnetically correlated along the growth axis, the in-plane magnetic domains are only of micron-order size and are thus not apparent in a specular measurement.

NiO-magnetite multilayers exhibit long range antiferromagnetic order with the magnetite ferrimagnetic correlations confined to a single layer due to stacking faults of the spinel structure at the interfaces[l, 2, 3, 4]. A systematic study of the field-dependence of the interlayer coupling in a series of NiO-magnetite multilayers has been made using neutron diffraction. Both NiO and magnetite single thin films were included in the measurements for comparison. In the magnetite film, intensity changes with magnetic field are consistent with domain reorientation of the net ferrimagnetic moments, while in the NiO film there are essentially no intensity changes. There is no significant field dependence of the magnetic correlation lengths in either film. For multilayers where the ratio of NiO to magnetite layer thickness is far from unity, the field dependence approximates that of the bulk films. However, for a Fe3O4(68Å)|NiO(34Å) multilayer the NiO antiferromagnetic intensity decreases with increasing field, and there is a broadening of the NiO peak on the order of 30 percent. Concomitantly, the magnetite spins rotate collinear with the field, as expected, due to the net 4.2 μB moment per unit-cell. The NiO moments appear to rotate into domains where the direction of propagation of the ferromagnetic sheets is closer to the field direction.

Neutron-diffraction studies of MnTe/CdTe superlattices with very thin CdTe spacers are reported. Results indicate the formation of spin helices (consistent with the tensile nature of strain in the MnTe layers) and coherence between the helices in different MnTe layers. Possible mechanisms for the interlayer correlations are discussed.

Recently developed nanocrystalline magnetic systems are of considerable interest fundamentally as well as technologically. One such material is Fe73.5B9Si13.5Cu1Nb3, which can be produced by heat treating the amorphous precursor. This forms a noncrystalline phase with typical dimension of 350 A as determined by neutron diffraction. Small angle neutron scattering (SANS) has been employed to investigate the properties of the nanocrystallized material over the temperature range from 10 K to 725 K, a regime where no significant structural changes are expected to occur. In zero field and low temperature (10K) we obtained an isotropic scattering pattern. The application of a relatively modest field to sweep out the domains changed the scattering to a "butterfly wings" pattern typical of patterns dominated by magnetic elastic intensity. Up to 450 K this pattern changed only modestly, while for substantially higher temperatures the ratio of inelastic to elastic scattering increased rapidly as the magnetic phase transition of the intergranular component (≃ 575 K) was approached. Triple axis inelastic measurements showed that the majority of the magnetic inelastic scattering was from the nanocrystalline phase.

A family of one-dimensional oxides was synthesized by solid state techniques and their structures determined by powder X-ray and powder neutron Rietveld refinement. The compounds are structurally related to A4PtO6 (A = Ca, Sr, Ba), which contains infinite chains of alternating face-sharing PtO6 octahedra and AO6, trigonal prisms. The compounds exhibit a variety of magnetic properties. The structures and magnetic properties of some of these one-dimensional oxides are discussed.

We performed neutron powder diffraction on solution-derived lead zirconate titanates (PZT). Three compositions, PZT 45/55, PZT 20/80 and PbTiO3, were investigated. The materials were annealed so that the perovskite phase had just begun to grow from the precursor phase. In our materials this precursor phase is the pyrochlore rather than fluorite phase. The results show that in the pyrochlore phase, the (Ti,Zr) and the Pb are ordered in their crystallographic sites while the O are essentially disordered in both of the two usual pyrochlore anion sites.

Neutron diffraction studies of tetragonal zirconia polycrystals (TZP) subjected to a varying applied uniaxial stress indicates that a ferroelastic crystalline transformation occurs within the bulk of the material. The critical coercive stress was determined to be (1.65±0.03) GPa for yttria stabilised TZP and (0.70±0.05) GPa for ceria stabilised TZP. The results agree well with previous reports concerning the ferroelasticity of tetragonal zirconia, and provide direct evidence indicating that the anomalies observed using the first X-ray diffraction studies originate from the bulk of the ceramic and not solely from the surface. The preferred orientation observed in the tetragonal crystallites was measured as a function of applied uniaxial stress and interpreted via a resolved stress criterion. It is believed that the ferroelastic transformation can act as an energy absorbing mechanism and hence toughen zirconia or ceramics containing dispersed zirconia.

The local atomic structure of (Pb1-x Lax)( Zry Ti1.y)1.x/4O3 (PLZT) has been examined by means of pair-distribution function (PDF) analysis derived from neutron powder diffraction. We find that atoms are displaced from the atomic sites in the average periodic structure by a significant amount. The directions and magnitudes of the atomic displacements in PLZT are very similar to those found in Pb(Mg1/3Nb2/3)O3 (PMN). The short- and intermediate-range structural changes between ferroelectric, relaxor and antiferroelectric PLZT phases were compared.

Doping Rare-earth (RE) elements to ZrO2 helps stabilize the cubic and tetragonal phases and improves resistance to thermal shock and sintering at high temperatures. Since a RE ion has a lower valency (3+) than Zr ion (4+), oxygen vacancies are formed to preserve electroneutrality. We have studied the crystal structure of La0.1Zro.9O1.95 and Nd0.1Zr0.9O1.95 by neutron diffraction and examined the associated oxygen defects by a Fourier transform of the filtered residual diffuse scattering. The hydration process was investigated by inelastic neutron-scattering measurements of the hydrogen vibrational density of states of the surface hydroxyl groups and physisorbed water on these fine powders. We compare the O-H stretch vibrations from samples with only surface hydroxyl groups to multilayer coverage of water molecules. The decreasing energies and increasing widths of the O-H stretch bands with increasing H2O coverage indicate the influence of hydrogen bonding on the motion of water molecules. Similar elastic and inelastic experiments were also performed on a high surface-area pure ZrO2 powder.

A review is presented of recent neutron diffraction studies of silicate and borate glasses, using a combination of steady-state reactor and pulsed neutron sources. The samples studied include both single component glasses and binary systems, consisting of a network modifier plus a network former, and the data have been extended to high magnitudes of the scattering vector, Q, to achieve high real-space resolution. Peak fitting techniques are employed to extract the detailed geometry of the basic structural units and to investigate the distortions caused by the introduction of network modifiers. The data are compared to various structural models and conclusions are drawn not only with regard to the validity of the structural models themselves but also concerning the environment of the network modifying cations.

Lead-indium phosphate glasses exhibit a number of useful properties such as a high index-of-refraction, low preparation temperature and melt viscosity, and good chemical durability. The structure of such a glass (composition in wt. %: 65 PbO, 29 P2O5, 6 In2O3) has been investigated by total neutron scattering using the GLAD diffractometer at Argonne's spallation neutron source IPNS. Peaks corresponding to the P-O, Pb-O/In-O, and 0-0 pairs were observed in the radial distribution function. The short-range structure in the glass, in terms of average coordination numbers and bond distances, is compared with those of a pure P2O5 glass and with the crystal structure of lead pyrophosphate, Pb2P2O7. Unlike silicate glasses in which the SiO4 tetrahedra form a 3-dimensional network, the PO4 tetrahedra in phosphate glasses form a chain-like structure. The structural modification by the lead cations in phosphate glasses appears to occur mainly in the medium range affecting the lengths and connectivity of the chain-like structure.

The neutron vibrational density of states has been determined from neutron time-of-flight scattering in g-Ge1-xSnxSe2 with x = 0, 0.3, 0.35, and 0.5 to search for "floppy" modes. Previously Raman and Mossbauer studies1 have been interpreted on the basis that the addition of Sn to the GeSe2 network reduces the average number of mechanical constraints per atom allowing one to tune through the rigidity percolation threshold near x = 0.35. A comparison of the VDOS measured in this work below 10 meV for all samples shows that they are nearly identical indicating no evidence of the existence of floppy modes in these samples. Ab initio molecular dynamics2 calculations of the VDOS show good agreement with the measured results for g-GeSe2.

Both neutron and X-ray scattering are used to determine the pair correlation functions (short-range order), the atomic displacements arising from atom size disparity, and the (derived) effective pair interactions in binary alloy solid solutions. This enterprise has taken on a new vitality through concomitant advances in both electronic theory and computer modeling of the atomic arrangements in alloys. An overview of the diffuse scattering formalism will be presented with an emphasis on the ways in which neutron scattering is particularly effective in sorting out the separate contributions to the total scattering pattern. Aspects of contrast variation and enhancement, and the utilization of both elastic and inelastic scattering will be discussed and examples of both past and recent work will be covered, including some future directions. We will also note briefly the relation between local order studies and details of the electronic and the elastic response functions of alloys.

A single crystal of α-Fe0.47Cr0.53 was annealed at 1100K, 5K above the a-phase transition temperature, for four days and then water quenched. A detailed investigation using X-ray synchrotron radiation was previously carried out to study the short-range order and static displacements in this alloy. The phonon dispersion curves, studied here by inelastic neutron scattering, appear typical of bcc alloys and the phonon groups are observed to be significantly broadened in the vicinity of the dip at ξ=2/3 in the longitudinal [ξ ξ ξ] phonon dispersion. In this paper we explore the possibility that nearly random concentration fluctuations and an extremely small difference in the atomic sizes, together with an appropriate lattice response function, can nonetheless produce elastic diffuse scattering indicative of a new phase.

Phonon softening was observed in the parent phase of a AuCd alloy which transforms from the β2(B2) parent to ζ2¹(trigonal) martensite. Since Cd strongly absorbs neutrons, the isotope 114Cd was used in preparing the single crystal for the measurements. The [ζζ0]TA2 phonon branch was measured and found to be anomalously low. A minimum is present at ζ=0.35 which softens with decreasing temperature towards Ms. The results are consistent with the model proposed by Ohba et al. based upon a crystallographic study of the ζ2¹ phase.

The nucleation stages of the decomposition reaction in a 58Ni-13at%Al alloy at T=450° C have been investigated by means of small- and wide-angle polarized neutron scattering. The use of the 58Ni isotope for the sample preparation tremendously reduced the incoherent scattering of the matrix. This, together with the application of polarized neutrons for experiments at T = 12 K, made the detection of extremely small Ni3Al clusters, not accessible to other microanalytical tools, with diameters D < 1 nm feasible.

Elastic neutron-scattering measurements on two samples of Cu alloyed with 1.3% Mn and 0.55% Mn show that the spin-density-wave (SDW) features found in more concentrated alloys persist in the limit of very dilute alloys. These features consist of temperature-dependent incommensurate peaks in magnetic neutron scattering, with positions and strengths which are fully consistent with those in the concentrated alloys. The implications of these measurements are twofold. First, it is clear from our data that SDW magnetic ordering occurs across the entire range of CuMn alloys which have typically been interpreted as spin glasses. Second, the more fundamental significance of this work is the suggestion via extrapolation that a peak in the magnetic susceptibility χ(q) occurs in pure copper, at a value of q given by the Fermi-surface diameter 2kF.

We investigated the magnetic excitations in polycrystalline samples of hard magnet related compounds DyFe4Al8 and DyMn4Al8 by neutron spectroscopy. For both compounds the magnetic spectra at energies below 40 meV are dominated by the response of the Dy3+ ions. In DyMn4Al8 we observed pure crystal-field transitions within the Dy3+ J=15/2 ground multiplet which is split into 8 doublets under the low point-group symmetry of 4/mmm. In DyFe4Al8 the Dy crystal-field-split states are perturbed by the molecular fields of the ordered Fe sublattice.

Lattice dynamics of γ-ZrH(D) ordered phases with essentially one-dimensional H-H (D-D) interaction was studied by inelastic neutron scattering. The experimental optic peaks were described within the Born-von Kármán model. The bound multiphonon states were observed in the spectra. Their binding energies were derived from the experimental data.