Showing papers in "Physica B-condensed Matter in 1989"
TL;DR: In this paper, magnetoresistance data up to 20 T and magnetisation measurements on the mixed-valence cubic perovskite semiconductor Nd 05 Pb 05 MnO 3 were presented, which demonstrated that the material orders ferromagnetically below 184 K and that around and above this temperature the conductivity is dominated by hopping of localized magnetic polarons, with an activation energy ∼95 meV.
Abstract: We present magnetoresistance data up to 20 T and magnetisation measurements on the mixed-valence cubic perovskite semiconductor Nd 05 Pb 05 MnO 3 , which demonstrate that the material orders ferromagnetically below 184 K, and that around and above this temperature the conductivity is dominated by hopping of localized magnetic polarons, with an activation energy ∼95 meV
580 citations
141 citations
TL;DR: CRYOPAD, a novel neutron polarimeter developed at ILL is described using this cryogenic device, precise general polarization analysis could be readily accomplished up to large scattering angles.
Abstract: CRYOPAD, a novel neutron polarimeter developed at ILL is described Using this cryogenic device, precise general polarization analysis could be readily accomplished up to large scattering angles Central to the method is the use of superconducting Meissner screens to establish clean magnetic segmentation and a “magnetic vacuum” sample chamber
107 citations
TL;DR: In this article, optical and electrical properties of the TlInX 2 (X = S, Se, Te) were studied, and the I-U -curves of the first two compounds are S-type with characteristic oscillations in the negative differential resistance (NDR) region while the sulfides show an Ohmic behavior.
Abstract: Optical and electrical properties of the TlInX 2 (X = S, Se, Te) were studied. The selenides and tellurides are of chain-like structure while the sulfides are layered. The measurements ( I-U characteristics and optical absorption) seem to have a direct connection with the main structural features. The I-U -curves of the first two compounds are S-type with characteristic oscillations in the negative differential resistance (NDR) region while the sulfides show an Ohmic behavior. The optical absorption measurements in the temperature range 15–300 K for Se- and Te-compounds show a positive temperature coefficient of the gap while for the S-compound it is negative. Possible explanations are mentioned.
90 citations
TL;DR: In this article, the assembly and experimental set-up of the superbender polarizers are described and the achieved flipping ratio and the transmission as a function of the wavelength are shown for some representative cases and compared with calculations for different collimations of the beam.
Abstract: After representative reflectivity curves of actually applied polarizing supermirrors the assembly and experimental set-up of the superbender polarizers is described. The achieved flipping ratio andthe transmission as a function of the wavelength are shown for some representative cases and compared with calculations for different collimations of the beam, showing that their properties are fully understood. Actual applications of the superbender polarizer with respective literature are given.
69 citations
TL;DR: In this paper, the theoretical behavior of reflectivity and transmission of multilayers using a complex index of refraction resulting from the optical theorem is calculated numerically by a complex matrix multiplication method.
Abstract: The theoretical behaviour of reflectivity and transmission of multilayers using a complex index of refraction resulting from the optical theorem is calculated numerically by a complex matrix multiplication method. It is applied to the antireflecting layer and for different layer sequences of supermirrors and compared with measurements. Resulting limits and some ways to overcome these are discussed.
67 citations
TL;DR: In this paper, the free energy expansion for a generalized system consisting of an arbitrary number of interacting magnetic contributions was given for a discussion of the type of magnetic transition in quasi-binary RE-Co2 compounds such as TbxHo1−xCo2.
Abstract: Inoue and Shimizu [1] give the free-energy expansion for a system consisting of a set of identical local (rare-earth) magnetic moments interacting with an itinerant electron subsystem (Co2). In this paper the free-energy expansion is given for a generalized system consisting of an arbitrary number of interacting magnetic contributions. This generalization is necessary for a discussion of the type of magnetic transition in quasi-binary RE-Co2 compounds such as TbxHo1−xCo2.
61 citations
TL;DR: In this article, the results of X-ray scattering studies of the rare earth metals and related new results for superlattices and thin slabs were reviewed and discussed in the context of lattice modulations.
Abstract: We review the results of X-ray scattering studies of the rare earth metals and present related new results for superlattices and thin slabs. In rare earth crystals we have observed weak structural modulations which accompany the magnetic ordering. The wave length of this modulation can be derived from a spin-slip model in accordance with symmetry considerations. X-ray scattering of both the charge and magnetization density modulations allow for highly accurate determination of the magnetic wave vector. The physical basis of our discussion is given in the context of lattice modulations. The implications of these results for the understanding of magnetic structure of rare earth superlattices are also discussed in the light of recent neutron diffraction studies of holmium-yttrium superlattices. The effect of the finite size of the magnetic block in a superlattice is considered and it is shown that significantly different behavior than in bulk is expected. In particular it is found that for thin slabs the ferromagnetic phase has the lowest energy.
61 citations
TL;DR: In this paper, a high-performance neutron velocity selector of the helical lamella type is presented (rotational speed 28 300 rpm, overall length 300 mm) and peak transmission remains high (81%) even at high resolution (10%) and large beam divergence (60′).
Abstract: A high-performance neutron velocity selector of the helical lamella type is presented (rotational speed 28 300 rpm, overall length 300 mm). The peak transmission remains high (81%) even at high resolution (10%) and large beam divergence (60′).
55 citations
TL;DR: The high magnetic field facility of Osaka University, equipped with several kinds of non-destructive magnets, is described in this paper, where the field strength produced for practical use is up to 80 T and time durations are from 0.4 ms to 40 ms.
Abstract: The high magnetic field facility of Osaka University, equipped with several kinds of non-destructive magnets, is described. The field strength produced for practical use is up to 80 T and time durations are from 0.4 ms to 40 ms. Various kinds of experiments, from physics to biology, are carried on there.
55 citations
TL;DR: In this article, the magnetic properties of a large group of compounds with the general formula R2Cu2O5, where R stands either for Sc, In and Lu, or the heavy rare-earth element from Tb to Yb, were investigated.
Abstract: We have investigated the magnetic properties of a large group of compounds with the general formula R2Cu2O5, where R stands either for Sc, In and Lu, or the heavy rare-earth element from Tb to Yb. All compounds investigated are isostructural and crystallize in the orthorhombic Ho2Cu2O5 type of crystal structure and show some magnetic transitions at low temperatures. These transitions are mainly associated with the spins on Cu2+ sites. However, a possible magnetic ordering of the rare-earth moments by these ternary oxides has also been discussed.
TL;DR: In this paper, a review of the experiments described in this paper shows that, when the 3He superfluids are rotated, many different vortex structures can be created and the vortex cores are large enough so that several details in their structure can be observed experimentally.
Abstract: The experiments described in this review show that, when the 3He superfluids are rotated, many different vortex structures can be created. The vortex cores are large enough so that several details in their structure can be observed experimentally. When probed with NMR, the vortices in 3He-B display both spontaneous and induced magnetization; their large magnetic moments reveal the existence of non-trivial vortex cores, consisting of magnetic superfluids. A first order phase change in the core structure, along a well defined transition line on the P-T-plane, appears a discontinuity in the magnetization of the rotating 3He-B. A similar transition, marked by a jump in the critical velocity for vortex creation, is also observed in hydrodynamic experiments. The most easily created vortices in 3He-A are doubly quantized and continuous. This identification is compatible with the results of NMR and negative ion experiments. The latter work reveals a focusing interaction between the ions and the vortex textures. Another, presumably singular vortex was also found in 3He-A by the ion technique in high magnetic fields. Gyroscopic measurements have demonstrated persistent currents in both superfluid phases of 3He. In addition, experimental data on vortex-free counterflow states, on critical velocities, on vortex states of 3He-A in restricted geometries and on mutual friction between the vortex lattice and the normal fluid are discussed.
TL;DR: In this article, the authors present resistivity, Hall and noise measurements for p- and n-Si between 77 and 300 K and show that 1f noise sources are located in the bulk.
Abstract: We present resistivity, Hall and noise measurements for p- and n-Si between 77 and 300 K. A 1f noise parameter α between 10-6 and 10-4 at 300 K and between 10-7 and 10-3 at 77 K is found in n- and p-Si. The α-value is independent of the effective volume. It is shown that 1f noise sources are located in the bulk. Hooge's empirical relation is confirmed in the case where an α-value of 10-6 is observed. The temperature dependence of the α-value is measured for n- and p-Si with doping concentrations between 1014 and 1018 cm-3. The magnitude of the α-value and its temperature dependence are related to the manufacturing process. Our measurements give no experimental support for the quantum 1f noise.
TL;DR: An automatic device for measurements of the magnetic moment in high d.c. magnetic fields up to 20 T produced by a Bitter coil is presented in this paper, where the extraction technique is used and a cryostat associated to a calorimeter permits us to cover the 1.4-500 K temperature range.
Abstract: An automatic device for measurements of the magnetic moment in high d.c. magnetic fields up to 20 T produced by a Bitter coil is presented. The extraction technique is used and a cryostat associated to a calorimeter permits us to cover the 1.4–500 K temperature range. The calibration, the accuracy and the sensitivity of the system are discussed.
TL;DR: In this paper, a macroscopic theory of superfluid turbulence is developed in which the vortex tangle is characterised by both its line-length density and its drift velocity.
Abstract: A macroscopic theory of superfluid turbulence is developed in which the vortex tangle is characterised by both its line-length density and its drift velocity. Three velocity fields are accordingly distinguished, viz. the mass velocity υ, the normal-fluid velocity υn and the drift velocity υe of the vortex tangle. The introduction of the drift velocity of the tangle as an additional variable seems to be new. The non-dissipative equations of motion are derived from a generalised form of Lin's variational principle. Both the energy and the impulse of the vortex tangle into account. It is shown that the effective mass density of the vortex tangle vanishes. In equilibrium the relative velocity of the vortex tangle is given by the derivative of the energy of the tangle with respect to the tangle impulse. A similar relation holds for a ring vortex in a fluid of infinite extent.
When dissipative terms are added to the equations according to the thermodynamics of irreversible processes the Vinen equation follows immediately. The derivation suggests a new interpretation of the right-hand member of the Vinen equation in terms of the derivative of a potential energy. A similar potential energy has been used in investigations on vortex nucleation and critical velocities. The theory is extended by including the effects of large gradients of the line-length density. The corresponding generalisation of the Vinen equation is presented.
TL;DR: In this article, local order in Se1−xTex has been investigated in liquid and supercooled state and it has been shown that the first coordination shell is a structural transition tightly correlated to the metal-nonmetal transition.
Abstract: Local order in Se1−xTex has been investigated in liquid and supercooled state. Analysis of the first coordination shell has shown in pure tellurium a structural transition tightly correlated to the metal-nonmetal transition, in a limited range of temperature, according to thermodynamics predictions. Similar analysis has been extended to Se0.1Te0.9 mixture.
TL;DR: In this paper, it was shown that the low temperature state of PbMg 1 3 Nb 2 3 O 3 (PMN) does not possess long-range ferroelectric order when cooled in zero applied electric field.
Abstract: Neutron scattering measurements on PbMg 1 3 Nb 2 3 O 3 ( PMN ) and Na 1 2 Bi 1 2 TiO 3 ( NBT ) have been performed and it was shown that the low temperature state of those crystals does not possess long-range ferroelectric order when cooled in zero applied electric field. The results of PMN measurements in an applied electric field are in agreement with the spin-glass-like model for the low temperature phase.
TL;DR: In this article, the effect of small amounts of detergents on the structure of small unilamellar lipid vesicles (SUV) has been investigated, and the results indicate that small amounts, e.g., bile acid, can be incorporated in the lipid membrane, which leads to a stabilization of the liposomes by electrostatic repulsion.
Abstract: The effect of small amounts of detergents on the structure of small unilamellar lipid vesicles (SUV) has been investigated. The results indicate that small amounts of charged detergents, e.g. bile acid, can be incorporated in the lipid membrane, which leads to a stabilization of the liposomes by electrostatic repulsion.
TL;DR: In this article, the phase and chirality of the helical order are preserved from one Dy layer to another, suggesting that the coupling is propagated by a spin-density-wave mechanism.
Abstract: Single crystal artificial superlattices prepared by molecular beam epitaxy and consisting of Dy, Er, and Gd layers alternated with Y all exhibit long-range magnetic order that is propagated through intervening non-magnetic Y layers as shown by neutron diffraction studies. In the case of Dy systems, the phase and chirality of the helical order are preserved from one Dy layer to another. The phase shift across the Y layer is proportional to the Y layer thickness, and so is in general a non-integral multiple of π, suggesting that the coupling is propagated by a spin-density-wave mechanism. The magnetic coherence range, obtained from a series of samples of constant Dy thickness and varying number of Y layers, shows a linear variation with the inverse of the Y layer thickness.
TL;DR: In this article, the authors used the complementarity of steady state and pulsed neutron sources to provide accurate data concerning the short range order of hydrogenated amorphous silicon, a-Si:H.
Abstract: Hydrogen is well known to play an important role in the electronic properties of hydrogenated amorphous silicon, a-Si:H. However, its precise location and thus the a-Si:H local order still remain uncertain. The aim of the present study, using the complementarity of steady state and pulsed neutron sources, is to provide accurate data concerning the short range order.
TL;DR: In polymer melts of protonated and deuterated polystyrene (PS and d-PS) surface segregation occurs at temperatures and compositions in the one phase region close to the coexistence curve for phase separation.
Abstract: In polymer melts of protonated and deuterated polystyrene (PS and d-PS) surface segregation of d-PS occurs at temperatures and compositions in the one phase region close to the coexistence curve for phase separation. Neutron reflection is capable of obtaining detailed information on surface segregation, as corroborated by a test on a polymer blend containing 10% volume fraction of d-PS where a thermal treatment caused a surface enrichment of d-PS up to 28%.
TL;DR: In this article, pressure cells designed for work on four-circle diffractometers equipped with an Eulerian cradle and pressures up to 2.5 GPa are described, and single crystalline sapphire anvils allow the optical inspection of the sample crystals, e.g., during in-situ crystal growth and the pressure measurement with the ruby fluorescence technique.
Abstract: Pressure cells designed for work on four-circle diffractometers equipped with an Eulerian cradle and pressures up to 2.5 GPa are described. Single crystalline sapphire anvils allow the optical inspection of the sample crystals, e.g., during in-situ crystal growth and the pressure measurement with the ruby fluorescence technique. Experiments on normal and deuterated ice VI are reported.
TL;DR: In this paper, a simple technique for focusing synchrotron radiation and thereby providing high intensity x-ray beams as small as 0.1 micron in diameter is described, where slowly tapered glass capillaries serve as the focusing elements.
Abstract: A simple technique for focusing synchrotron radiation and thereby providinghigh intensity x-ray beams as small as 0.1 micron in diameter is described. Gradually tapered glass capillaries serve as the focusing elements. The first measurements of gain in the intensity of x-rays using focusing capillaries have been made.
TL;DR: In this article, the magnetic properties of hexagonal GdGa2 and GdCu5 compounds have been investigated by measurements on resistivity, susceptibility and magnetization, and the unusual magnetic properties and the behaviour of the low temperature resistivity seem to be related to the incommensurate magnetic structure in compounds without magnetocrystalline anisotropy.
Abstract: The magnetic properties of the hexagonal GdGa2 and GdCu5 compounds have been investigated by measurements on resistivity, susceptibility and magnetization. Their magnetic structure has also been studied by neutron diffraction at a very short wavelength where the absorption cross section of gadolinium is not too high. Below TN = 22K, the neutron diffraction pattern of GdGa2 can be interpreted with a cycloidal structure with the propagation vector Q = (0.39, 0.39, 0). Below TN = 26K, GdCu5 orders in an incommensurate triangular structure associated with a propagation vector Q = (13, 13, 0.223). The unusual magnetic properties and the behaviour of the low temperature resistivity seem to be related to the incommensurate magnetic structure in compounds without magnetocrystalline anisotropy.
TL;DR: In this article, high-field magnetization curves of Ho 2 Co 17 and Ho 2 Fe 14 B were analyzed in terms of crystal-and molecular-field interactions, and the magnetic moments are slightly tilted out of the hexagonal plane as a result of crystalfield (CF) interactions.
Abstract: High-field magnetization curves of Ho 2 Co 17 are analyzed in terms of crystal- and molecular-field interactions The magnetic moments are slightly tilted out of the hexagonal plane as a result of crystal-field (CF) interactions A full set of CF parameters for the two non-equivalent rare-earth ions in the hexagonal structure has been evaluated reconciling Mossbauer, inelastic-neutron-scattering, specific-heat and high-magnetic-field results Exchange interactions between the 3d and 4f spins in the Ho 2 Co 17 and Ho 2 Fe 14 B compounds are compared and discussed
TL;DR: In this article, the local structure of Co(II) sorbed from aqueous solution on wet surfaces of γ-Al 2 O 3 and TiO 2 (rutile) in-situ was characterized.
Abstract: Co K-edge fluorescence-yield EXAFS spectroscopy was used to characterize the local structure of Co(II) sorbed from aqueous solution on wet surfaces of γ-Al 2 O 3 and TiO 2 (rutile) in-situ. On both solids at the same surface coverage (≈1.5 μmoles/m 2 ), sorbed Co is coordinated by six oxygens at 2.08 A. On γ-Al 2 O 3 , each Co has an average of four second-neighbor Co (at 3.12 A), one second-neighbor Al (at 3.20 A), and one distant neighbor Co (at 6.1 A). On TiO 2 , each Co has an average second-neighbor shell consisting of about one Co (at 3.36 A), one Ti (at 3.31 A), and no detectable distant neighbors. These results indicate that Co is bonded to the oxide surfaces as inner-sphere complexes and that no significant precipitation of Co-hydroxide or diffusion of Co into the oxides has occured. Differences between the two sorption systems indicate formation of multinuclear Co complexes on γ-Al 2 O 3 and of less polymerized Co complexes on TiO 2 , suggesting that the type of oxide influences the nature of the sorption complex formed.
TL;DR: In this article, the basic concepts for constructing the dissipation functions in the equations of motion for the magnetization of a ferromagnet were reviewed, taking into account the conservation laws for the total magnetic moment.
Abstract: We state in this review the basic concepts for constructing the dissipation functions in the equations of motion for the magnetization of a ferromagnet. The procedure for constructing the dissipation functions is analogous to the one used to construct the internal energy of a ferromagnet, taking into account the conservation laws for the total magnetic moment.