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We carried out neutron powder diffraction experiments on the cluster-based Haldane compound fedotovite K2Cu3O- (SO4)3. Weak magnetic reflections caused by a magnetic long-range order appeared below an antiferromagnetic transition temperature TN = 3.1 K. We propose a possible magnetic structure that is consistent with the magnetic properties reported in the literature. [ABSTRACT FROM AUTHOR]

The magnetic structure of NdPd5Al2 has been studied by neutron powder diffraction. We observed the magnetic reflections with the modulation vector q = (1/2,0,0) below the ordering temperature TN. We found a collinear magnetic structure with a Nd moment of 2.7(3) μB at 0.5 K parallel to the c-axis, where the ferromagnetically ordered a-planes stack with a four-Nd-layer period having a ++−− sequence along the a-direction with the distance between adjacent Nd layers equal to a/2 (magnetic space group Panma). This “stripe”-like modulation is very similar to that in CePd5Al2 with q = (0.235, 0.235, 0) with the Ce moment parallel to the c-axis. These structures with in-plane modulation are a consequence of the two-dimensional nature of the Fermi surface topology in this family, originating from the unique crystal structure with a very long tetragonal unit cell and a large distance of >7Å between the rare-earth layers separated by two Pd and one Al layers. [ABSTRACT FROM AUTHOR]

The phonon-dispersion relations for cubic PbTi03 (Tc = 763 K) have been determined along the [1,0,0], [1,1,0], and [1,1,1] directions at ? = 793 ? using inelastic neutron scattering. A set of the transverse optical (TO) branches drops sharply toward the zone center. The TO phonon curves for cubic PbTi03 are nearly isotropic, in contrast to the distinct q dependence of the TO branches for tetragonal PbTi03. The zone-center TO mode energy softens with decreasing temperature from 1173 to 793 K. Moreover, the transverse acoustic (TA) branch along [ξ,ξ,ξ] shows significant softening around ξ = 0.25 and 0.5. The anomaly around the midpoint suggests a tendency toward forming a fourfold periodicity along the [1,1,1] direction, whereas the anomaly toward the R point results from the softening of the oxygen octahedron rotation. These two anomalies persist up to 1173 ? and are weakly temperature dependent. The TA branches along [1,0,0] and [1,1,0] soften in the entire q range as the temperature approaches Tc. Although the phonon softening occurs simultaneously, the softening of the zone-center TO mode plays an important role in the single phase transition. The phonon dispersion relations for PbTiO3 are discussed in connection with the simple perovskite oxides and the Pb-based relaxors. [ABSTRACT FROM AUTHOR]

The article discusses the highlights of the Ninth International Conference on Neutron Scattering held at the Knoxville Conference Center in Tennessee from May 3-7, 2009. The event started with a welcome reception on May 3 wherein scientists from 29 countries met. A technical program also started with the welcome of the chairs of the conference which include Simon Billinge and Thomas Mason. Some of the topics addressed in the conference sessions include soft matter and biology, chemistry and earth sciences, and iron pnictide superconductors.

Owing to their overall low energy scales, flexible molecular architectures, and ease of chemical substitution, molecule-based multiferroics are extraordinarily responsive to external stimuli and exhibit remarkably rich phase diagrams. Even so, the stability and microscopic properties of various magnetic states in close proximity to quantum critical points are highly under-explored in these materials. Inspired by these opportunities, we combined pulsed-field magnetization, first-principles calculations, and numerical simulations to reveal the magnetic field–temperature (B–T) phase diagram of multiferroic (NH4)2FeCl5⋅H2O. In this system, a network of intermolecular hydrogen and halogen bonds creates a competing set of exchange interactions that generates additional structure in the phase diagram—both in the vicinity of the spin flop and near the 30 T transition to the fully saturated state. Consequently, the phase diagrams of (NH4)2FeCl5⋅H2O and its deuterated analog are much more complex than those of other molecule-based multiferroics. The entire series of coupled electric and magnetic transitions can be accessed with a powered magnet, opening the door to exploration and control of properties in this and related materials. [ABSTRACT FROM AUTHOR]

We present a comprehensive single-crystal neutron diffraction investigation of the Mn1-xCoxWO4 with 0.02 ≼x ≼ 0.30. At lower concentration ≼0.05, the system is quickly driven into the multiferroic phase with spin structure forming an elliptical spiral order similar to the parent compound. The reduction of electric polarization is ascribed to the tilting of the spiral plane. For x ˜ 0.075, the magnetic structure undergoes a spin-flop transition that is characterized by a sudden rotation of the spin helix envelope into the ac plane. This spin structure persists for concentration up to x =0.15, where additional competing magnetic orders appear at low temperature. For 0.17 ≼x ≼ 0.30, the system experiences another spin-flop transition and recovers the low-x spiral spin configuration. A simple commensurate spin structure with q = (0.5,0,0) is found to coexist with the incommensurate spiral order. The complex evolution of magnetic structure in Co doped MnW04 contrasts sharply with other transition metal ion doped Mn1-xAxWO4 (A = Zn, Mg, Fe) where the chemical substitutions stabilize only one type of magnetic structure. The rich phase diagram of Mn1-xCoxWO4ub> results from the interplay between magnetic frustration and spin anisotropy of the Co ions. [ABSTRACT FROM AUTHOR]

The spin-wave excitations of the multiferroic MnWO4 have been measured in its low-temperature collinear commensurate phase using high-resolution inelastic neutron scattering. These excitations can be well described by a Heisenberg model with competing long-range exchange interactions and a single-ion anisotropy term. The magnetic interactions are strongly frustrated within the zigzag spin chain along the c axis and between chains along the a axis, while the coupling between spin along the b axis is much weaker. The balance of these interactions results in the noncollinear incommensurate spin structure associated with the magnetoelectric effect, and the perturbation of the magnetic interactions leads to the observed rich phase diagrams of the chemically doped materials. This delicate balance can also be tuned by the application of external electric or magnetic fields to achieve magnetoelectric control of this type of materials. [ABSTRACT FROM AUTHOR]