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Recent documents in Scholars' Mineen-usWed, 24 May 2017 01:51:45 PDT3600Beaver bridge
http://scholarsmine.mst.edu/professional_theses/337
http://scholarsmine.mst.edu/professional_theses/337Fri, 12 May 2017 06:18:06 PDT
“The Little Beaver Bridge is situated on the A. & P. R. R., 3 ¾ S. W. of Rolla it is built on the “Howe Truss” plan and spans a valley through which flows the “Little Beaver Creek” - it has two approaches (stringers supported by trestles), the length of the northern one is 38 ft., while that of the southern one is 35’5”. The bridge is composed of 5 spans and is supported on 6 piers; the length of the bridge proper is 687’ 2”, with the abutments it is 760’7”. The piers are of sandstone and have a batir, from about one half of their height to the top, of one inch to the foot. In consequence of the comparatively small size of the used in their construction, the Railroad Company has commenced to tear them down in order to erect larger piers. The dimensions of the new piers (for the bottom course) will be 13’1” x 30’ instead of 7’6” x 24’3” as in the old one - the batir will however in the new piers start from the second course. All the timber used in this bridge (except the ties which are oak) is white pine"--pages 5-6.
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James E. McGrath<p>Truss bridges -- Design and construction -- Missouri</p>Mössbauer Effect Study of Reduction of Ilmenite
http://scholarsmine.mst.edu/phys_facwork/754
http://scholarsmine.mst.edu/phys_facwork/754Mon, 08 May 2017 07:17:26 PDTR. Immele-Meziou et al.Superconductivity and Magnetism in Ternary Rare-earth Compounds
http://scholarsmine.mst.edu/phys_facwork/753
http://scholarsmine.mst.edu/phys_facwork/753Fri, 05 May 2017 11:32:44 PDT
Superconductivity and magnetism are two types of order that can take place in materials at low temperatures. When the magnetic order is ferromagnetic, a competition exists between magnetism and superconductivity. Neutron scattering has been used to measure the interaction of magnetism and superconductivity in a series of ternary rare-earth alloys. A wide range of behavior is found near the magnetic transition, including mean-field magnetic ordering, first-order transitions between magnetism and superconductivity, and co-existence of ferromagnetism and superconductivity with a sinusoidally-modulated magnetic phase.
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Herbert A. Mook et al.Neutron Scattering Studies of the Magnetic Ordering in Ternary Rare Earth Compounds
http://scholarsmine.mst.edu/phys_facwork/752
http://scholarsmine.mst.edu/phys_facwork/752Fri, 05 May 2017 11:32:40 PDTHerbert A. Mook et al.Neutron Scattering Studies of Magnetic Superconductors
http://scholarsmine.mst.edu/phys_facwork/751
http://scholarsmine.mst.edu/phys_facwork/751Fri, 05 May 2017 11:32:36 PDT
Results obtained in the last few years by neutron diffraction on the nature of the magnetic ordering in magnetic superconductors are reviewed. Emphasis is given to studies of the complex intermediate phase in ferromagnetic superconductors where both superconductivity and ferromagnetism appear to coexist.
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Sunil K. Sinha et al.Magnetic and Crystallographic Properties of LaNi<sub>(5-x)</sub>Fe<sub>x</sub>
http://scholarsmine.mst.edu/phys_facwork/750
http://scholarsmine.mst.edu/phys_facwork/750Fri, 05 May 2017 11:32:33 PDT
The magnetic and crystollographic properties of LaNi_{(5-x)}Fe_{x}, samples (l ≤ x ≤ l.4) have been studied by x-ray diffraction, neutron diffraction, SQUID and Mössbauer spectroscopy. Samples with x ≥ 1.2 display typical ferromagnetic behavior. The substitution of iron for nickel in LaNi_{5}, increases the unit cell volume and Curie temperature. The majority (> 90%) of the Fe atoms appear to occupy the 3g site. Induced Ni magnetic moments at 30K have been calculated using the bulk magnetization data and iron magnetic moments.
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C. Y. Tai et al.High-pressure Cell for Neutron Scattering
http://scholarsmine.mst.edu/phys_facwork/749
http://scholarsmine.mst.edu/phys_facwork/749Fri, 05 May 2017 11:32:30 PDT
We have developed a high-pressure cell for neutron scattering. The cell uses a barrel-shaped support cylinder made of sintered ceramics. Samples 6 mm in diameter and 10 mm long can be accommodated. The cell is suitable for use at low and high temperatures, after a pressure generated at room temperature is locked. The change of pressure on cooling to cryogenic temperatures is estimated by measuring the lattice parameter of NaCl. Besides the pressure locking technique, continuous pressurization can be achieved at room temperature by using a built-in mini-press while the cell is mounted on a goniometer of neutron spectrometer.
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Akifumi Onodera et al.Determination of the Thickness Distribution for Randomly Oriented, Independently Scattering Polydisperse Systems of Platelets
http://scholarsmine.mst.edu/phys_facwork/748
http://scholarsmine.mst.edu/phys_facwork/748Fri, 05 May 2017 11:32:27 PDT
A method has been developed for using small-angle X-ray scattering data to compute the thickness distribution function for systems of randomly oriented, independently scattering platelets with constant electron density and with different thicknesses. Each platelet is assumed to have a uniform thickness. The dimensions defining the faces of the platelet are assumed to be large compared to the platelet thickness. Under these conditions, if the thickness distribution function &ro;(a) is defined so that &ro;(a)da is the probability that the platelet thickness lies in the interval between a and a + da, &ro;(a) is found to be given by the Fourier transform of a quantity which can be evaluated from the experimental scattering curve. Some differently weighted average thicknesses can be calculated from the scattering curve without evaluating the Fourier transform. The function p(a) and the average thickness have been evaluated from the experimental scattering curves for two charcoal samples in which the voids are assumed to have the form of platelets.
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Oran Allan Pringle et al.Neutron and Magnetic Studies of La<sub>0.7</sub>Sr<sub>0.3</sub>Mn<sub>1-x</sub>Cr<sub>x</sub>O<sub>3</sub>(x ≤ 0.7): A Homogeneous Charge-Ordered System
http://scholarsmine.mst.edu/phys_facwork/747
http://scholarsmine.mst.edu/phys_facwork/747Fri, 05 May 2017 11:32:24 PDT
Structural and magnetic properties of La_{0.7}Sr_{0.3}Mn_{1-x}Cr_{x}O_{3} (0 < x ≤ 0.7) have been studied in order to determine the effect of substitution of Cr^{3+} for Mn^{3+}. The data consist of neutron and x-ray powder-diffraction and magnetization measurements. We previously suggested these systems transition from ferromagnetic to antiferromagnetic ordering with the intermediate concentrations containing coexisting ferromagnetic and antiferromagnetic domains. Upon further detailed examination, we find that the neutron data can be fit using a single homogeneous long-range magnetically ordered state and compositionally dependent charge ordering. The magnetic structures are controlled by the competition between Mn-Mn, Mn-Cr, and Cr-Cr interactions (double exchange and superexchange). The metal to semimetal and semimetal to insulator transitions can be quantitatively described as due to the localization effect of superexchange. The presence of charge ordered states in the insulating region arises from the favorable energetics of Mn^{4+}-O-Cr^{3+} superexchange bonds relative to Mn^{3+}-O-Cr^{3+} bonds.
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Thomas F. Creel et al.Neutron-Diffraction Study of γ-Fe at High Pressure
http://scholarsmine.mst.edu/phys_facwork/746
http://scholarsmine.mst.edu/phys_facwork/746Fri, 05 May 2017 11:32:20 PDT
Face-centered-cubic iron (γ-Fe) coherently precipitated in a single crystal of Cu has been studied by neutron diffraction at high pressures up to 0.9 GPa and in the temperature range from about 5 to 110 K. It undergoes antiferromagnetic ordering at 67±2 K at ambient pressure. The ordering temperature T_{N} monotonically decreases with increasing pressure following a relation T_{N}(K)=67-12.8p - 11.1p^{2} - 6.17p^{3}, where p is in units of GPa. The change of T_{N} in γ-Fe is discussed in terms of the volume change caused by pressurization or by alloying.
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Oran Allan Pringle et al.Magnetism and Superconductivity in (Er<sub>0.16</sub>Ho<sub>0.84</sub>)Rh<sub>4</sub>B<sub>4</sub>
http://scholarsmine.mst.edu/phys_facwork/745
http://scholarsmine.mst.edu/phys_facwork/745Fri, 05 May 2017 11:32:17 PDT
The superconducting and ferromagnetic phase boundaries in the (Er_{1-x}Hox)Rh_{4}B_{4} mixed ternary alloy system meet in a multicritical point at x_{cr} ≈ 0.9. For xcr, the compounds first become superconducting as the temperature is lowered, and then lose superconductivity in a transition to ferromagnetism. The coexistence of superconductivity and ferromagnetism for alloys near the erbium-rich end of the phase diagram is well established. It has also been suggested that ferromagnetism and superconductivity coexist in alloys with x just below x_{cr}. We have carried out neutron-diffraction, ac magnetic susceptibility, and heat-capacity measurements on a sample of (Er_{0.16}Ho_{0.84})Rh_{4}B_{4} to investigate the possibility of coexistence of ferromagnetism and superconductivity for x ≈ x_{cr}. We find that there are minor discrepancies in the superconducting and magnetic transition temperatures reported for different samples of (Er_{0.16}Ho_{0.84})Rh_{4}B_{4}, but that ferromagnetism and superconductivity do occur simultaneously over a narrow temperature range in this sample. We suggest that an inhomogeneous state occurs, consisting of separate ferromagnetic and superconducting regions, rather than microscopic coexistence.
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Oran Allan Pringle et al.High-Pressure Neutron-Scattering Studies of Graphite and Stage-Two Graphite-SbCl<sub>5</sub>
http://scholarsmine.mst.edu/phys_facwork/744
http://scholarsmine.mst.edu/phys_facwork/744Fri, 05 May 2017 11:32:14 PDT
The longitudinal-acoustic (LA) phonons propagating along the c axis in highly oriented pyrolytic graphite (HOPG) were investigated as a function of pressure up to 20 kbar using inelastic-neutron-scattering techniques. The phonon frequencies varied as (P,q)=A(P)sin[c(P)q/2], where A(P) and c(P) indicate the pressure dependences of the zone-center LO frequency of B_{1g1} symmetry and of the c-axis lattice spacing, respectively. From the measurements, the mode Grüneisen parameter for the LA branch was estimated to be 1.5 x 10^{-2} kbar^{-1} (independent of q); the elastic constant C_{33} for HOPG was found to be 3.40 x 10^{11} dyn/cm^{2} at 1 bar with a pressure coefficient of (1/C_{33})(dC_{33}/dP)=2.91 x 10^{-2} kbar-1. The measured c-axis spacings were 6.71 and 12.72 Å for HOPG and stage-2 SbCl_{5}-intercalated graphite, respectively, at atmospheric pressure; the corresponding compressibilities (1/c)(dc/dP) were -2.24 x 10^{-3} kbar^{-1} (HOPG) and -2.28 x 10^{-3} kbar^{-1} (SbCl_{5}). Elastic-neutron-scattering studies up to 20 kbar were undertaken to search for stage transformations, but no evidence of any phase transition was observed.
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B. Alzyam et al.Time-dependent Magnetic Structures of the Superconducting Mixed Ternary System Ho(Rh<sub>1-x</sub>Ir<sub>x</sub>)<sub>4</sub>B<sub>4</sub>
http://scholarsmine.mst.edu/phys_facwork/743
http://scholarsmine.mst.edu/phys_facwork/743Fri, 05 May 2017 11:32:10 PDT
Magnetic structures have been determined by netron diffraction for several compositions in the superconducting mixed ternary system Ho(Rh_{1-x}Ir_{x})_{4}B_{4}. Two features previously reported to occur in the heat capacity for some compositions are shown to correspond to successive magnetic transitions. For x=0.30 and 0.45, neutron diffraction peaks for the lowest temperature structure develop over a timescale of many hours. The results are discussed in terms of magnetic frustration.
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Steven E. Lambert et al.Neutron-diffraction Study of the Magnetic Ordering in Ni(CH<sub>2</sub>CO<sub>2</sub>NH<sub>2</sub>)<sub>2</sub> 2 H<sub>2</sub>O
http://scholarsmine.mst.edu/phys_facwork/742
http://scholarsmine.mst.edu/phys_facwork/742Fri, 05 May 2017 11:32:07 PDT
The magnetic structure of Ni(CH_{2}CO_{2}NH_{2})_{2} 2 H_{2}O has been determined by the analysis of neutron-diffraction data from powder and single-crystal samples. Ni(CH_{2}CO_{2}NH_{2})_{2} 2 H_{2}O orders at a Néel temperature of 0.88 K. The magnetic structure consists of antiferromagnetically coupled layers having a canted ferromagnetic ordering within layers, with a moment of (2.33 ± 0.14)μ_{B} per Ni^{2+} ion. The magnetic unit cell is composed of two crystallographic unit cells, and contains four nickel atoms. The moment direction is not simply related to either crystalline or molecular symmetry axes.
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Akifumi Onodera et al.X-ray Investigation of the Critical Exponent η in Argon
http://scholarsmine.mst.edu/phys_facwork/741
http://scholarsmine.mst.edu/phys_facwork/741Fri, 05 May 2017 11:32:03 PDT
Measurements were made of the small-angle x-ray scattering intensity from argon near the critical point. After the scattering curves are corrected for all known effects except those resulting from irrelevant variables, a value of the critical exponent η=0.09±0.02 is obtained, while if a correction for the estimated effect of irrelevant variables is also made, η=0.03±0.03. The scattering data for argon therefore show that if irrelevant variables can be neglected, the critical exponent η for argon is in good agreement with the value obtained by Warkulwiz, Mozer, and Green from small-angle neutron scattering data for neon. These values of η, however, are clearly greater than those obtained by calculations using high-temperature expansions and renormalizationgroup techniques. On the other hand, if the effects of irrelevant variables are given by the estimate used in correcting the scattering data, the η value computed from the scattering curves agrees with the theoretical results.
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Harold D. Bale et al.Structural and Magnetic Properties of La<sub>0.7</sub>Sr<sub>0.3</sub>Mn<sub>1-x</sub>Ni<sub>x</sub>O<sub>3</sub> (x ≤ 0.4)
http://scholarsmine.mst.edu/phys_facwork/740
http://scholarsmine.mst.edu/phys_facwork/740Fri, 05 May 2017 11:32:00 PDT
We have studied the structural and magnetic properties of La_{0.7}Sr_{0.3}Mn_{1-x}Ni_{x}O_{3} (x = 0.05, 0.1, 0.20, 0.30, and 0.40) perovskites using x-ray and neutron diffraction and magnetic measurements. Our data consist of neutron (γ = 1.479Å) and x-ray (γ = 1.5481Å; Cu Kα) powder diffraction and magnetization measurements. We previously suggested these systems transition from ferromagnetic to antiferromagnetic ordering with the intermediate concentrations containing coexisting domains of ferromagnetically and antiferromagnetically ordered states. Upon further detailed examination, we find that the samples are homogeneous and that neutron data can be fitted to a single long-range magnetically ordered state. The compositional dependent changes are driven by a shift in the dominant near neighbor interaction from ferromagnetic to antiferromagnetic. In the intermediate compositions, peaks previously identified as due to antiferromagnetic ordering, in fact arise from charge ordering; the system remains in a ferromagnetic state where the Ni moments are antiparallel to the Mn moments. This interpretation supersedes multiphase and spin glass models for these complex systems.
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Thomas F. Creel et al.Small-angle neutron scattering of (Er<sub>0.8</sub>Ho<sub>0.2</sub>)Rh<sub>4</sub>B<sub>4</sub>
http://scholarsmine.mst.edu/phys_facwork/739
http://scholarsmine.mst.edu/phys_facwork/739Fri, 05 May 2017 11:31:56 PDT
The (Er_{1-x}Ho_{x})Rh_{4}B_{4} pseudoternary alloy system has a minimum in the phase boundary between the superconducting and ferromagnetic phases near x=0.3. This minimum has been identified as due to the competing magnetic anisotropies of Er and Ho. It has also been suggested that there could be a Lifschitz point near the minimum. Using the 30-m SANS camera at the National Center for Small-Angle Scattering Research at ORNL, we have observed a peak in the SANS pattern for (Er _{0.8}Ho_{0.2})Rh_{4}B_{4} at Q=0.065 Å^{-1}. This peak appears for temperatures between T_{c}2, measured upon cooling, and T_{m}, and corresponds to a modulation of the magnetic moment with a wavelength of about 100 Å, demonstrating that the modulated moment phase exists away from the ErRh _{4}B_{4} end of the phase diagram. The wavelength of the modulation is the same as was previously observed in ErRh_{4}B _{4}. The fact that the wavelength of the modulation remains finite near x=0.3 appears to rule out the possibility of Lifschitz behavior near this point.
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Oran Allan Pringle et al.