Present issue of the Journal titled“Recent studies by neutron scattering”is overviewed, and the relation between crystallography and neutron scattering experiments is discussed. Current status of neutron facilities available in Japan such as KUR, KENS and JRR3M are also shown.
Recent neutron scattering studies of the static and dynamical properties of percolating magnets with fractal geometry are reviewed. In particular, direct observation of the fractal dimension, time-resolved experiments on kinetics of ordering of fractal clusters, observation of fraction excitations and anomalous diffusive motions in percolating antiferromagnets are now in progress by using neutron magnetic scattering techniques.
Most of low dimensional lattice magnets undergo magnetic transitions into long range ordered phases due to extra interactions in addition to the ordinal nearest neighbor exchange interaction. The competition among these interactions gives rise to a variety of magnetic phases having incommensurate structure and partially disordered structure. These structures appear in the transition scheme of successive phase transition including fast order transition. The transiton belongs to a new universality class in some cases. External magnetic field also gives remarkable changes in the magnetic structure. Low dimensionality of the lattice favors quantum effect such as Haldane gap.
Crystal and magnetic structures of the title hard magnets were determined by means of neutron and X-ray powder diffraction measurements. A high-resolution diffractometer, JRR3M-HRPD, was utilized for the measurements done at temperatures in the range from 15K to ambient. Rietveld profile-fitting technique was applied for the analysis. It is demonstrated that reliable structural parameters and magnetic moments of magnetic atoms can be determined reasonably for the above complicated crystal systems.
Compositional microstructures in magnetic recording films, Co-Cr alloys, were studied by using small-angle neutron scattering (SANS), transmission electron microscopy and nuclear magnetic resonance techniques. Magnetic microdomains whose size correlated well with that of the compositional microstructures were also observed by using SANS technique. The size of the microstructures was smaller than crystal grain size. These results demonstrate that the compositional structures promote the magnetic microstructures suitable for high density recording.
Two topics of the recent neutron scattering works on the strongly correlated electron systems are presented. We first discuss the origin of the cross-over from a heavy electron state to a ferromagnetically ordered state in CeSix based on the results of the neutron elastic and inelastic scattering experiments. Next, we show recent finding of interesting magnetic structures of the low carrier density system CeP under magnetic field. The result evidences the existence of a magnetic polaron state in CeP and its formation of the layered lattice structure among the normal Ce ion lattice under the field.
Crystal structures of high-Tc superconductors have been reviewed on the basis of neutron diffraction results. It is shown that the oxygen atoms play a crucial role in controlling hole concentration on the CuO2 layer, which determines the occurrence of superconductivity. Close correlation between Tc and hole concentration in nonstoichiometric YBa2Cu3O7-Z and YBa2Cu4O8 under pressure, oxygen location and occupancy in Tl-and Hg-based superconductors in connection with superconductivity and a novel structure in the newly-discovered superconductor containing the CO3 group are presented.
Cu-Al-Ni alloys with composition close to Cu3Al show pseudoelasticity associated with transformations among four martensitic phases, γ1', β1' β1'', α1'. The crystallographic information was obtained by neutron diffraction techniques using the four-circle neutron diffractometer at Researcch Reactor Institute of Kyoto University, KUR, Japan. A small tensile jig with a load cell and an extensometer was attached for generating high uniaxial stress. Quadrant slit devices were inserted into the neutron beam path for accurate measurement of diffracting conditions. Strains as second rank tensors were described as a function of hysteresis and stress between 50 and 460 MPa.
Experimental studieds on the kinetics of the phase transition of Ni3Mn, Fe-B-Si and Mn67Cu33 utilizing the Wide-Angle Neutron Diffractometer (WAND) at the Oak Ridge National Laboratory are reviewed. Specially designed diffractometer WAND is introduced.
Phase separation process associated with ordering is discussed in conjunction with normal “spinodal decomposition process”. An Al1-xLix alloy system is one of such systems, in which, homogeneous ordering takes place priory to phase separation of δ' (Al3Li) precipitates in a matrix. To study the relation between phase separation and ordering processes, super-lattice reflection together with small-angle neutron scattering in an A1-9.5%Li alloy has been studied. Comparisons between normal phase separation process and phase separation with ordering are also given.
Substances containing Hydrogen bond show phase transitions of various types. Among them, those undergoing frerroelectric phase transitions attract attention of scientists because of its drastic change in physical properties and its simplicity in model accessible by theoretical method. Due to its difference in scattering power of hydrogen atom for X-rays and for thermal neutrons, application of neutron diffraction technique to this field becomes increasing. Single crystal neutron diffraction studies on this subject carried out at Kyoto University Reactor (KUR) are mainly reviewed. Starting from neutron diffraction apparatus, recent development in hydrogen bond studies, analysis of ferroelastics, problems in deuterium substitution, agreement factor in structure analysis are discussed. Survey is also given on some of the non-hydrogen-bonded ferroelectrics.
Application of neutron diffraction to physico-chemical studies of molecular solids is reviewed with examples taken from the recent work exploiting combination of the new experimental method with existing ones such as calorimetry. The substances discussed are Fullerene C60 with its order-disorder and glass transitions, ice and other hydrogen bonded systems, clathrate crystals where the host-guest as well as the guest-guest interaction is important, and a group of ammonium compounds in which deuterium substitution causes phase transitions to occur at low temperature where there is none in the hydrogenous analogues.
The structure factors of simple liquid metals as Na, Mg and Al have been obtained above each melting temperature by neutron and X-ray diffraction with sufflclent accuracy. The X-ray and neutron diffraction results indicate a small but clear difference, form which the electron density distribution and electron-ion correlation functions have been evaluated.
In Microemulsion System In order to investigate critical phenomena at phase separation in 3-component microemulsion system, small angle neutron scattering experiments were carried out at Risø National Laboratory. A temperature variation of a forward scattering indicated the meanfield critical behavior at the “near-critical region.” The van der Waals free energy with Flory-Huggins parameter was introduced to explain observed spinodal and binodal points.
The structural characteristics of the blue-colored poly (vinyl alcohol) (PVA) -iodine complex (PIC) in aqueous solution were studied by means of small-angle neutron scattering with contrast variation method, using various D2O/H2O. The concentrated PIC solutions were prepared by using PVA with the degree of polymerization of 15, containing excess KI and the color inducing agent CuCl2. The results from the computer simulation for the measured Stuhrmann plot with theoretical scattering functions suggested that the PIC forms a cylindrical aggregate compposed of the complexed units of more than 4 (insert space) linearchains of PVA surrounding triiodide dimer.
Small-angle neutron scattering (SANS) studies on the miscibility, critical phenomena and phase transitions by spinodal decomposition of polymer mixtures are reviewed. SANS with the “deuterium labeling technique” is a powerful technique to study one-phase state of polymer mixtures. Interaction parameters, phase diagrams, critical exponents, etc. can be obtained for the one-phase mixtures of deuterated and undeuterated polymers. Time-resolved SANS is extremely useful to study early stage of spinodal decomposition and local structure such as interphases and thermal concentration fluctuations in the coexisting domains in the later stage of spinodal decomposition of polymer mixtures.
Neutron scattering experiments have been shown to provide useful information about the properties subcellular structures. Two experimental examples carried out by our group are briefly reviewed. One is the structure determination of the HU protein-DNA complex. HU protein plays a role not only packing long DNA but also affecting transcription and replication of active DNA. Our results indicate that HU protein might bend DNA in a cell. The other is the observation of the crystallization process of lysozyme from the microscopic molecular level. We found that the pre-crystallization process started even in the unsaturated solutions.
Lipophorin, a circulating lipoprotein in insects, was investigated by a neutron small-angle scattering method with H2O/D2O contrast variation. The scattering profiles were similar to those obtained by X-ray small-angle scattering results. Considering location of each constituent, we proposed a radially symmetrical three-layer model of lipophorin; an inner core of hydrocarbons surrounded by a layer of diacylglycerol and apolipophorin-II, and a spherical micellar arrangement of the outer hydrophilic surface formed by apolipophorin-I and polar phospholipid headgroups. The detailed structure basis is essential to understand the tissues specific recognition mechanism of lipophorin for loading and unloading lipids at respective tissues.
Recombinant yeast-derived human hepatitis B virus surface antigen vaccine particle was investigated by small-angle neutron scattering using contrast variation method. Contrast matching point of the particle was determined at 24% D2O content, indicating most of the non-protein components of the particle to be both lipids and hydrocarbons from yeast. However, the protein distribution is significantly different from that of lipids or hydrocarbons as indicated by the intensity profile difference at 40% D2O content solution from that of other D2O content solutions. The Stuhrmann plot is indicative of the fact that the antigenic protein is slightly dominant in the peripheral region of the spherical vaccine particle.