Neutron diffraction investigation of the magnetic structure of the Mn2Sb pnictide at high pressures

This paper reports on the results of investigations into the influence of high pressures (up to 5.3 GPa) at T=300 K on the magnetic structure of the Mn₂Sb pnictide. The crystal and magnetic structures of the Mn₂Sb compound are studied using a direct neutron diffraction method. It is demonstrated that the magnetic ferrimagnet-antiferromagnet phase transition, which is observed in a number of Mn₂Sb-based substitutional solid solutions upon chemical compression of the Mn₂Sb crystal lattice, does not occur in the Mn₂Sb compound under high pressures in the aforementioned range due to an anisotropic pressure-stimulated strain in the Mn₂Sb lattice. At pressures P≥2.8 GPa, the Mn₂Sb compound is characterized by a spin reorientation with respect to the tetragonal axis and the basal plane of the crystal lattice.     

Neutron diffraction investigation of MnAs under high pressure

Powdered MnAs has been investigated by neutron diffraction in a pressure cryostat, at hydrostatic pressures up to 13 kbar and temperatures down to 4.2 K. It has been found that in the orthorhombic MnP type structure, which under pressure is retained at low temperature, a spiral magnetic structure with propagation vector τ_a = 0.125X2πX a¹ at 12.6 kbar is formed.     

Neutron diffraction investigation of the magnetic ordering of TiBe2

A neutron diffraction measurement on a polycrystalline sample of TiBe₂ did not reveal any onset of antiferromagnetic ordering at temperatures as low as 1.4 K. The maximum value of the ordered magnetic moment on titanium which might have gone undetected in the present experiment is shown to be 0.2 Bohr magnetons for a transverse spin density wave of arbitrary periodicity.     

X-ray diffraction investigation into the specific features of the growth kinetics of oxygen-containing precipitates in Czochralski-grown silicon crystals

The formation and growth of defects (precipitates and dislocation loops) during isothermal decomposition of a supersaturated oxygen-containing solid solution in Czochralski-grown silicon crystals are investigated using triple-crystal x-ray diffractometry. It is established that oxygen-containing precipitates grow through diffusion and that the formation of dislocation loops is associated with both the coagulation of embedded silicon atoms and the generation of dislocation loops by stresses induced in the vicinity of the oxygen-containing precipitates.     

On the investigation of surface structure by reflection high energy electron diffraction (RHEED)

RHEED (Reflection High Energy Electron Diffraction) has been used to investigate surface structures. A formalism which allows fast, precise determination of the sizes, shapes and relative orientation of the lattices of well-ordered surface structures from the distances between the diffraction lines has been developed. This formalism is illustrated by the analysis of copper, gold and silicon surfaces and various surface structures formed on these. The relative precision of the measurements can in special cases be of the order of 10^?4 and will in general be better than 10^?3.     

Neutron diffraction studies of the structure of substituted complex cobalt oxides

The effect of substitution of manganese and niobium for cobalt on the magnetic and crystal structure of doped cobaltites has been studied by the neutron diffraction method. The Pr_0.5Sr_0.5Co_{1 ? x} Mn _x O₃ samples undergo, with increasing x, a series of transitions of the crystal structure from the monoclinic I2/a to orthorhombic Immm phase, and then, to the high-temperature tetragonal I4/mcm phase and low-temperature orthorhombic Fmmm phase. Undoped Pr_0.5Sr_0.5CoO₃ is a ferromagnet, but the magnetic ordering is destroyed with increasing x. At high degrees of substitution of manganese, the A-type antiferromagnetic ordering is observed. Substitution of niobium for cobalt in La_{1 ? x} Sr _x CoO₃ compositions leads to changes in the Co-O bond length and the unit cell volume, which is accompanied by a decrease in the ferromagnetic moment. The Co → Nb substitution prevents the formation of Co⁴⁺ and leads to the stabilization of Co³⁺ in a high-spin state.     

Neutron powder diffraction investigation on the crystal and magnetic structure of (Ho(0.50+x)Ca(0.50-x))(Mn(1-x)Cr(x))O3

The crystal and magnetic structure of (Ho(0.50+x)Ca(0.50-x))(Mn(1-x)Cr(x))O(3) (x = 0.00, 0.01, 0.02, 0.03) has been investigated between 5 and 300 K by means of neutron powder diffraction followed by Rietveld refinement and dc magnetic measurements. During cooling an orthorhombic to monoclinic phase transition occurs on account of the charge and orbital ordering taking place in the Mn sub-lattice; at low temperature phase separation takes place and the main monoclinic phase coexists with a secondary orthorhombic phase, whose amount slightly increases with the increase of Cr content. Cr(3+) is not involved in orbital ordering or superexchange interactions. The charge and magnetic ordering are decoupled: the Mn moments order according to a CE-type structure in all samples.     

Neutron diffraction study of (NH4I)0.73(KI)0.27

Powder and single crystal neutron diffraction experiments were performed on (NH₄I)_0.73(KI)_0.27 and provide experimental evidence for the occurence of a new phase below 63K. This ε phase has trigonal symmetry (space group R3m) and was, so far, not observed in the ammonium halides. It can be characterized by an almost undistorted NaCl lattice, with two in-equivalent NH₄ sites of the four NH₄ molecules per unit cell. The NH₄ group at the trigonal axis (the former cubic <111> axis) is almos perfectly tetrahedral. The other three NH₄ molecules are 0.18 Å off center and exhibit C_3v symmetry with the polar axis along the remaining three body diagonals. Hence, this ε phase reveals a complex dipolar order with a residual moment along the trigonal axis.     

Neutron diffraction study of (NH4I)0.73(KI)0.27

Powder and single crystal neutron diffraction experiments were performed on (NH₄I)_0.73(KI)_0.27 and provide experimental evidence for the occurence of a new phase below 63K. This ε phase has trigonal symmetry (space group R3m) and was, so far, not observed in the ammonium halides. It can be characterized by an almost undistorted NaCl lattice, with two in-equivalent NH₄ sites of the four NH₄ molecules per unit cell. The NH₄ group at the trigonal axis (the former cubic <111> axis) is almos perfectly tetrahedral. The other three NH₄ molecules are 0.18 Å off center and exhibit C_3v symmetry with the polar axis along the remaining three body diagonals. Hence, this ε phase reveals a complex dipolar order with a residual moment along the trigonal axis.     

Neutron diffraction investigation of the microstructure of lead-potassium melt bubbled with heavy water

The results of neutron diffraction microstructure investigation of a eutectic lead-potassium melt bubbled with heavy water are presented. The structure factors and pair correlation functions for pure eutectic and eutectic bubbled with heavy water are compared. Evidence of the presence of deuterium in the latter melt has been shown in the diffraction pattern.     

Neutron diffraction investigation of the temperature variation of the sublattice magnetisation of nickel sulphide

Single crystal neutron diffraction has been used to measure the temperature variation of the sublattice magnetisation of antiferromagnetic Ni_0.991S between 5 K and the conductivity transition temperature 223 K, T_t, at which the ordered moments suddenly vanish. The data cannot be explained consistently with those from other measurements using a localised-spin model, and help to support existing evidence that the antiferromagnetism in NiS is due to itinerant electrons.     

Neutron diffraction study of the magnetic structure of Na2 RuO 4

We present a novel model to simulate real social networks of complex interactions, based in a system of colliding particles (agents). The network is build by keeping track of the collisions and evolves in time with correlations which emerge due to the mobility of the agents. Therefore, statistical features are a consequence only of local collisions among its individual agents. Agent dynamics is realized by an event-driven algorithm of collisions where energy is gained as opposed to physical systems which have dissipation. The model reproduces empirical data from networks of sexual interactions, not previously obtained with other approaches.     

X-ray diffraction investigation of the structure of propolis films

The structure of films of a biological organic material (propolis) on inorganic substrates is investigated for the first time. It is established that, despite the complex chemical composition (involving more than 300 different components), the propolis films prepared from an alcohol solution on amorphous glass substrates and on semiconductor substrates with a small number of dangling bonds have a crystal structure.     

Neutron diffraction investigation of structural and magnetic states of lithium-doped antiferromagnet NiO

The elastic neutron scattering in polycrystalline samples of the (Ni_1−x Li_x)O solid solutions (x<0.1) is investigated by neutron diffraction technique. It is shown for the first time that the doping of nickel monoxide by lithium is accompanied by the formation of vacancies in the anionic sublattice, and the vacancy concentration is equal to the lithium content in the solid solution. The neutral lithium atoms are randomly arranged over sites of the cationic sublattice with possible spatial polarization of a valence electron toward an oxygen vacancy. In the composition range studied, the diamagnetic dilution of nickel monoxide by lithium turns out to be magnetically similar to the dilution with magnesium. In both cases, the Néel temperature and the mean magnetic moment per atom linearly decrease with an increase in concentration of the diamagnetic dopant.     

Neutron diffraction study and specific heat of antiferromagnetic NiI2

A neutron diffraction study has been carried out on a sample of powder of NiI₂: the spectrum at 4.2 K shows only a single magnetic line which cannot be indexed on the 2C lattice. Measurements of the specific heat capacity in the region of the transition show the existence of two peaks at the temperatures T₁=76K and T₂=59.5K, which correspond to singularities in the magnetisation.     

Neutron diffraction studies of water

Neutron diffraction measurements have been made for heavy water at five temperatures in the range 11–75°C using the diffractometers D2 and D4 at ILL. A first-order difference method has been used to determine the change in the intermolecular contributions to the observed cross-section. Fourier transformation techniques are used to give the changes in the real space distribution function. The results confirm the preliminary observations obtained in an earlier experiment and give a more precise indication of the structural variation. A detailed analysis shows that the intermolecular OD separation which corresponds to an effective hydrogen bond distance increases as the temperature rises. At larger distances there is a systematic but more complex variation which may be attributed to a change in the relative orientations of neighbouring molecules.     

Neutron diffraction determination of the magnetic structure of Dy PO4

Dy PO₄ is antiferromagnetically ordered below 3.39 K. The spin-structure is described by an antiparallel arrangement of nearest neighbours along the crystallographic c-axis. The magnetic moment at 1.8 K is (9.0±0.3) μ_β. These results confirm that Dy PO₄ may be considered as an ideal three-dimensional Ising system.     

Neutron capture gamma ray investigation of Sr88 level structure

The level structure of Sr⁸⁸has been investigated at the Karlsruhe research reactor FR2 using thermal neutron capture in Sr⁸⁷. A pure thermal neutron beam was obtained by Bragg reflection from a lead single crystal. The target was natural strontium which gives a cross section contribution of about 87% for the reaction Sr⁸⁷(n,γ) Sr⁸⁸. High resolution measurements of the capture gamma ray spectrum have been performed by means of a 4 cm² × 0.5 cm lithium-drifted germanium diode. 146 gamma lines have been observed. Cascade relationships were studied by a double and triple coincidence apparatus containing 4″Ø × 5″ NaI(Tl) crystals and XP-1040 photomultipliers. In several cases coincident background was subtracted utilizing the doublewindow technique. By application of the triple sum coincidence method capture gammas from isotopes other than the investigated Sr⁸⁸ nucleus could be eliminated. Several new levels were established. A transition scheme is proposed and discussed. The neutron binding energy of Sr⁸⁸ is determined to be 11111±4 keV.     

Neutron diffraction study of the orientational disorder in Ni(ND3)6Br2

The ND₃ group is in the high temperature phase of the title compound dynamically disordered. Fourier maps derived from the analysis of neutron single crystal Bragg data with phases based on a split atom and a Frenkel model show uniquely that each D₃ group has four density maxima occupying the corners of a square. Neither one nor three dimensional models of purely rotational disorder can describe the observations adequately.