[en] We observed in EuNi₂(Si_0.15Ge_0.85)₂ a very sharp, first-order valence transition from an Eu²⁺ to an Eu³⁺ state at around T_v∼42 K. The transition presents a large thermal hysteresis of 10 K. The huge entropy change associated with the valence transition gives rise to a barocaloric effect, which may find use in magnetic cooling by the application of pressure

[en] We report measurements of the evolution of the diffuse scattering in a single crystal PbMg1/3Nb2/3O3 as a function of hydrostatic pressure. Upon applying pressure the diffuse scattering intensity decreases and is suppressed at about 3 GPa, while no change in the line shape is observed. Correlations between Pb displacements, diffuse scattering and relaxor properties are discussed.

[en] We present high pressure-high temperature neutron diffraction data of α-iron in the 0-8 GPa and 300-550 K range. We find the isochors of α-iron strictly parallel to those of ε-iron, except at high P/T when the α-γ-ε triple point to the non-magnetic γ- and ε-phases is approached. This gives evidence for magnetoelastic effects in α-iron at high P/T. The measurements have been made possible by the use of a cell which enables neutron diffraction by external heating in the 0-10 GPa range and to at least 550 K. The technique should have numerous applications in research on condensed matter using neutrons.

[en] The origin of higher-order exchange interactions in localized S-state systems has been the subject of intensive investigations in the past. In particular, it has been suggested that a biquadratic exchange term may arise from the magnetoelastic energy. Here we report on the pressure and temperature dependence of the excitation spectra of magnetic Mn²⁺ dimers in CsMn_0.28Mg_0.72Br₃ probed by inelastic neutron scattering. Biquadratic exchange and a strong distance dependence of the bilinear exchange are observed. It is shown that the mechanism of local exchange striction may explain the occurrence of biquadratic exchange in accordance with the elastic properties of the compound

[en] We present a method which allows high-quality powder neutron diffraction patterns to be obtained under pressure by angle-dispersive diffraction to at least 10 GPa. This technique uses a new type of Paris-Edinburgh press in conjunction with sintered boron nitride anvils. As an example, we show NiO diffraction patterns obtained under purely hydrostatic pressures up to 10 GPa. These data were collected within a few hours, and are free from any contaminating signal from the pressure cell. High-resolution nuclear and magnetic structural information can be readily extracted by Rietveld refinements, without additional data correction. This technique will allow powder neutron diffraction at elevated pressures to become a standard tool on continuous neutron facilities

[en] We present a neutron diffraction study of liquid water to 6.5 GPa and 670 K. From the measured structure factors we determine radial and angular distributions. It is shown that with increasing density water approaches a local structure common to a simple liquid while distorting only a little the tetrahedral first-neighbor coordination imposed by hydrogen bonds that remain intact

[en] Neutron spectroscopy has been applied in order to elucidate the magnetothermal properties of the lanthanide alloys Er_xPr_1-x (x=0.6,0.8). The observed crystal-field splittings are in accordance with the arithmetically weighted crystal fields of the two pure metals. A mean-field approach is presented, which couples the two effective internal fields originating from the Er and Pr ions. The model is successful in explaining many of the observed magnetic properties, including the ferrimagnetic arrangement of the Er and Pr moments, the values of the respective moments, the magnetocaloric effect for x=0.7 and the large increase of the magnetic entropy at low temperatures due to the addition of Pr. A large single-ion anisotropy is derived and it is predicted that an enhanced magnetocaloric effect should be observed in single-crystal samples for x∼0.7 with the external magnetic field applied along the c axis. Additional magnetization measurements under pressure up to 0.72 GPa have shown no evidence for a pronounced sensitivity of the magnetic ordering temperature upon pressure in Er_0.6Pr_0.4

[en] We have investigated the chemical structure of PbMg_1/3Nb_2/3O₃ (PMN) relaxor ferroelectric at room temperature under hydrostatic pressures up to 8.37 GPa and at ambient pressure as a function of temperature. The refinement of the crystal structure shows that the amplitude of the displacements of the Pb ions from the (0 0 0) position decreases with increasing pressure. On the other hand, the thermal displacement parameters of Mg/Nb ions are almost insensitive to pressure. The decrease in the Pb displacements correlates with an increase in the anisotropy in the thermal displacement parameter of the O ions. These results are in agreement with those obtained in PbMg_1/3Ta_2/3O₃ (PMT) and show further evidence that the Pb displacements play an important role in the relaxor behavior. The aim of this study is to clarify the microscopic origin for the anomalous pressure effects observed in relaxors as well as to provide new data for the understanding of this class of materials

[en] Single-crystal neutron diffraction was employed to study the magnetic transition in the pseudobinary Laves-phase compounds Er_1-xY_xCo₂ (x=0, 0.4) under external magnetic fields up to 4 T. The magnetic scattering amplitudes measured for the reflections to which either the localized 4f Er moment or the itinerant 3d Co moment solely contributes, give direct evidence that the onset of long-range magnetic order for both magnetic sublattices occurs at about the same temperature T_C∼35.9 and 17.0 K for x=0 and 0.4, respectively. The magnetic-susceptibility and specific-heat data, obtained on the same specimens, were also measured. In agreement with the neutron-diffraction data the macroscopic measurements showed no multiple phase transitions as opposed to earlier measurements on powder samples, which are presented and discussed as well

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