Search

Panther is a new high-flux medium-resolution direct-geometry thermal-neutron time-of-flight spectrometer at the Institut Laue-Langevin (ILL). It is designed for inelastic neutron-scattering measurements of excitations in condensed matter using single crystals, polycrystalline samples, and liquids. Panther uses double focusing graphite or Cu monochromators, a Fermi chopper, and position-sensitive 3He detectors covering 2 steradians of solid angle. A system of disc choppers and an optional sapphire filter are used to reduce the epithermal neutron background. Thermal neutron background is reduced by a radial oscillating collimator, a beam dump, and an elaborate set of Cd shielding inside the evacuated detector tank. The outside of the tank is covered by a 0.3 m thick layer of borated high-density polyethylene to reduce ambient and cosmic background. The design and performance of the instrument in its current status are described, as well as planned developments.

The ground states of the frustrated pyrochlore oxide Tb2+xTi2-xO7+y have been studied by inelastic neutron scattering experiments. Three single-crystal samples are investigated; one shows no phase transition (x = -0.007 < xc ~ -0.0025), being a putative quantum spin-liquid (QSL), and the other two (x = 0:000, 0:003) show electric quadrupole ordering (QO) below Tc ~ 0.5 K. The QSL sample shows continuum excitation spectra with an energy scale 0.1 meV as well as energy-resolution-limited (nominally) elastic scattering. As x is increased, pseudospin wave of the QO state emerges from this continuum excitation, which agrees with that of powder samples and consequently verifies good x control for the present single crystal samples. [ABSTRACT FROM AUTHOR]

Non-centrosymmetric metals with tetragonal structure are characterized by an antisymmetric Rashba-type spin-orbit interaction, which has been predicted to give rise to anomalous spin susceptibility. Our polarized inelastic neutron scattering measurements in the normal phase of the heavy-fermion superconductor CePt3 Si confirm this prediction. We find that for a finite wave vector along the crystallographic a-direction the spin susceptibility Χaa is different from Χbb by a factor of two. The effect is even larger than in theoretical calculations based on the Hubbard model, and we speculate that this is due to the strong spin-orbit coupling of rare-earth heavy fermions. [ABSTRACT FROM AUTHOR]

YTiO 3 with T c &nvsim;30 K has been studied by the MARI spectrometer with E i =130 and 500 meV at T =5, 40 and 200 K. We have not found any clear orbital excitation in a wide Q - E range ( 0.5< Q <25 Å -1 , 6< E <350 meV ). The intensity of orbital excitation would be significantly weak in comparison with the phonon. † Present address: CEA/Grenoble, 38054 Grenoble Cedex 9, France. [ABSTRACT FROM AUTHOR]

The mineral linarite, PbCuSO4(OH)2, is a spin-1/2 chain with frustrating nearest-neighbor ferromagnetic and next-nearest-neighbor antiferromagnetic exchange interactions. Our inelastic neutron scattering experiments performed above the saturation field establish that the ratio between these exchanges is such that linarite is extremely close to the quantum critical point between spin-multipolar phases and the ferromagnetic state. We show that the predicted quantum multipolar phases are fragile and actually suppressed by a tiny orthorhombic exchange anisotropy and weak interchain interactions in favor of a dipolar fan phase. Including this anisotropy in classical simulations of a nearly critical model explains the field-dependent phase sequence of the phase diagram of linarite, its strong dependence of the magnetic field direction, and the measured variations of the wave vector as well as the staggered and the uniform magnetizations in an applied field. [ABSTRACT FROM AUTHOR]

Single-chain magnets (SCMs) are one-dimensional coordination polymers or spin chains that display slow relaxation of the magnetization. Typically their static magnetic properties are described by the Heisenberg model, while the description of their dynamic magnetic properties is based on an Ising-like model. The types of excitations predicted by these models (collective vs localized) are quite different. Therefore we probed the nature of the elementary excitations for two SCMs abbreviated Mn2 Ni and Mn2 Fe, as well as a mononuclear derivative of the Mn2 Fe chain, by means of high-frequency electron paramagnetic resonance spectroscopy (HFEPR) and inelastic neutron scattering (INS). We find that the HFEPR spectra of the chains are clearly distinct from those of the monomer. The momentum transfer dependence of the INS intensity did not reveal significant dispersion, indicating an essentially localized nature of the excitations. At the lowest temperatures these are modified by the occurrence of short-range correlations. [ABSTRACT FROM AUTHOR]

We report the low temperature magnetic properties of the pyrochlore Pr2Hf2O7. Polycrystalline and single-crystal samples are investigated using time-of-flight neutron spectroscopy and macroscopic measurements, respectively. The crystal-field splitting produces a non-Kramers doublet ground state for Pr3+, with Ising-like anisotropy. Below 0.5 K ferromagnetic correlations develop, which suggests that the system enters a spin-ice-like state associated with the metamagnetic behavior observed at μ0Hc∼2.4 T. In this regime, the development of a discrete inelastic excitation in the neutron spectra indicates the appearance of spin dynamics that are likely related to cooperative quantum fluctuations. [ABSTRACT FROM AUTHOR]

In this paper, we experimentally study and model the electron donating character of an axial diamagnetic Pd 2+ ion in four metalloligated lanthanide complexes of formula [PPh 4 ][Ln{Pd(SAc) 4 } 2 ] (SAc - = thioacetate, Ln = Tb, Dy, Ho, and Er). A global model encompassing inelastic neutron scattering, torque magnetometry, and dc magnetometry allows to precisely determine the energy level structure of the complexes. Solid state nuclear magnetic resonance reveals a less donating character of Pd 2+ compared to the previously reported isostructural Pt 2+ -based complexes. Consequently, all complexes invariably show a lower crystal field strength compared to their Pt 2+ -analogues. The dynamic properties show an enhanced single molecule magnet behavior due to the suppression of quantum tunneling, in agreement with our model.

Spin correlations of the frustrated pyrochlore oxide Tb 2+ x Ti 2- x O 7+ y have been investigated by using inelastic neutron scattering on single-crystalline samples ( x = -0.007, 0.000, and 0.003), which have the putative quantum-spin-liquid (QSL) or electric-quadrupolar ground states. Spin correlations, which are notably observed in nominally elastic scattering, show short-range correlations around L points [ q = ( 1 2 , 1 2 , 1 2 ) ] , tiny antiferromagnetic Bragg scattering at L and Γ points, and pinch-point-type structures around Γ points. The short-range spin correlations were analyzed using a random-phase approximation (RPA) assuming the paramagnetic state and two-spin interactions among Ising spins. These analyses have shown that the RPA scattering intensity well reproduces the experimental data using temperature- and x -dependent coupling constants of up to tenth-neighbor site pairs. This suggests that no symmetry breaking occurs in the QSL sample and that a quantum treatment beyond the semiclassical RPA approach is required. Implications of the experimental data and the RPA analyses are discussed.

We report on inelastic neutron scattering measurements of the antiferromagnetic NdPd 5 Al 2 compound. NdPd 5 Al 2 crystallizes in the tetragonal I4/mmm space group and exhibits a distinct uniaxial anisotropy due to crystal field effects. In this study, we have revealed the crystal field energy levels of NdPd 5 Al 2 composed of five Kramers doublets. The corresponding four inelastic excitations are located at energies 3.0 meV, 7.4 meV, 8.6 meV and 17.1 meV. We additionally interpreted the neutron spectra within a crystal field model. It has been established that the crystal field parameters found by a Monte Carlo technique and the derived ground-state wavefunctions consisting primarily of the [Formula: see text] states reproduce correctly magnetic susceptibility data.