Juscelino B. Leao

Lattice collapse and quenching of magnetism in CaFe[subscript 2]As[subscript 2] under pressure: A single-crystal neutron and x-ray diffraction investigation

Single-crystal neutron and high-energy x-ray diffraction measurements have identified the phase lines corresponding to transitions among the ambient-pressure paramagnetic tetragonal (T), the antiferromagnetic orthorhombic (O), and the nonmagnetic collapsed tetragonal (cT) phases of

Quasielastic and inelastic neutron scattering investigation of fragile-to-strong crossover in deeply supercooled water confined in nanoporous silica matrices

{\text{CaFe}}_{2}{\text{As}}_{2}

Role of random electric fields in relaxors

. We find no evidence of additional structures for pressures of up to 2.5 GPa (at 300 K). Both the T-cT and O-cT transitions exhibit significant hysteresis effects, and we demonstrate that coexistence of the O and cT phases can occur if a nonhydrostatic component of pressure is present. Measurements of the magnetic diffraction peaks show no change in the magnetic structure or ordered moment as a function of pressure in the O phase, and we find no evidence of magnetic ordering in the cT phase. Band-structure calculations show that the transition into the cT phase results in a strong decrease in the iron

Coupled Magnetic and Ferroelectric Domains in Multiferroic Ni3V2O8

3d

Neutron scattering measurements of the phonon density of states of FeSe 1 − x superconductors

density of states at the Fermi energy, consistent with a loss of the magnetic moment.

Static and dynamic Jahn-Teller effect in the alkali metal fulleride salts A4C60 (A=K,Rb,Cs)

We investigated, using quasi-elastic and inelastic neutron scattering, the slow single-particle dynamics of water confined in laboratory synthesized nanoporous silica matrices, MCM-41-S, with pore diameters ranging from 10 to 18 A. Inside the pores of these matrices, the freezing process of water is strongly inhibited down to 160 K. We analysed the quasi-elastic part of the neutron scattering spectra with a relaxing-cage model and determined the temperature and pressure dependence of the Q-dependent translational relaxation time and its stretch exponent β for the time dependence of the self-intermediate scattering function. The calculated Q-independent average translational relaxation time shows a fragile-to-strong (FS) dynamic crossover for pressures lower than 1600 bar. Above this pressure, it is no longer possible to discern the characteristic feature of the FS crossover. Identification of this end point with the predicted second low-temperature critical point of water is discussed. A subsequent inelastic neutron scattering investigation of the librational band of water indicates that this FS dynamic crossover is associated with a structural change of the hydrogen-bond cage surrounding a typical water molecule from a denser liquid-like configuration to a less-dense ice-like open structure.

Effects of pressure on the dynamics of an oligomeric protein from deep-sea hyperthermophile

Significance Relaxors are characterized by a frequency-dependent peak in the dielectric permittivity and are critical to modern technological applications because they exhibit large dielectric constants and unparalleled piezoelectric coefficients. Despite decades of study a fundamental understanding of the origin of relaxor behavior is lacking. Here we compare the structural, dynamical, dielectric, and piezoelectric properties of two highly similar piezoelectric lead-oxide materials: ferroelectric PbZr1–xTixO3 and relaxor Pb(Mg1/3Nb2/3)1–xTixO3. Random electric fields are implicated as the genesis of relaxor behavior, and the diffuse scattering associated with short-range polar order is identified as the order parameter. The piezoelectric response is found to be greatly amplified in crystals that display this diffuse scattering. PbZr1–xTixO3 (PZT) and Pb(Mg1/3Nb2/3)1–xTixO3 (PMN-xPT) are complex lead-oxide perovskites that display exceptional piezoelectric properties for pseudorhombohedral compositions near a tetragonal phase boundary. In PZT these compositions are ferroelectrics, but in PMN-xPT they are relaxors because the dielectric permittivity is frequency dependent and exhibits non-Arrhenius behavior. We show that the nanoscale structure unique to PMN-xPT and other lead-oxide perovskite relaxors is absent in PZT and correlates with a greater than 100% enhancement of the longitudinal piezoelectric coefficient in PMN-xPT relative to that in PZT. By comparing dielectric, structural, lattice dynamical, and piezoelectric measurements on PZT and PMN-xPT, two nearly identical compounds that represent weak and strong random electric field limits, we show that quenched (static) random fields establish the relaxor phase and identify the order parameter.

Reply to Soper: Density measurement of confined water with neutron scattering

Electric control of multiferroic domains is demonstrated through polarized magnetic neutron diffraction. Cooling to the cycloidal multiferroic phase of Ni3V2O8 in an electric field E causes the incommensurate Bragg reflections to become neutron spin polarizing, the sense of neutron polarization reversing with E. Quantitative analysis indicates the E-treated sample has a handedness that can be reversed by E. We further show a close association between cycloidal and ferroelectric domains through E-driven spin and electric polarization hysteresis. We suggest that a definite cycloidal handedness is achieved through magnetoelastically induced Dzyaloshinskii-Moriya interactions.

Antiferromagnetic critical pressure in URu 2 Si 2 under hydrostatic conditions

Inelastic neutron-scattering experiments have been carried out on polycrystalline samples of the

Effect of pressure on the quantum spin ladder material IPA-CuCl3.

{\text{FeSe}}_{1\ensuremath{-}x}