Pressure effects on the magnetic structure in La0.5Ca0.5-xSrxMnO3 (0.1 -< x -< 0.4) manganites

The effect of high pressure (0 - 8 GPa) on the magnetic structure of polycrystalline samples of La0.5Ca0.5-xSrxMnO3 (0.1 -< x -< 0.4) manganites at 5 K is investigated using neutron diffraction technique. Application of pressure is found to modify the previously reported magnetic structure, observed under ambient conditions, in these compounds [I. Dhiman et al., Phys. Rev. B 77, 094440 (2008)]. In x = 0.1 composition, at 4.6(2) GPa and beyond, A-type antiferromagnetic structure is found to coexist with CE-type antiferromagnetic phase, observed at ambient pressure, with TN ~ 150 K. For x = 0.3 sample, as a function of pressure the CE-type phase is fully suppressed at 2.3(1) GPa and A-type antiferromagnetic phase is favored. Further Sr doping at x = 0.4, the A-type antiferromagnetic phase is observed at ambient pressure and for T < TN (~ 250K). This phase is retained in the studied pressure range. However, the magnetic moment progressively reduces with increasing pressure, indicating the suppression of A-type antiferromagnetic phase. The present study brings out the fragile nature of the CE-type antiferromagnetic state in half doped manganites as a function of pressure and disorder \sigma 2. We observe that pressure required for destabilizing the CE-type antiferromagnetic state is reduced with increasing disorder \sigma 2. External pressure and changing A-site ionic radii have analogous effect on the magnetic structure.Comment: 9 pages, 6 figures, 1 table, To appear in Physical Review

Proton diffusivity in the BaZr0.9Y0.1O3−δ proton conductor

The thermally activated proton diffusion in BaZr0.9Y0.1O3−δ was studied with electrochemical impedance spectroscopy (IS) and quasi-elastic neutron scattering (QENS) in the temperature range 300-900K. The diffusivities for the bulk material and the grain boundaries as obtained by IS obey an Arrhenius law with activation energies of 0.46eV and 1.21eV, respectively. The activation energies obtained by IS for the bulk are 0.26eV above 700K and 0.46eV, below 700K. The total diffusivity as obtained by IS is by one order of magnitude lower than the microscopic diffusivity as obtained by QENS. The activation energies obtained by QENS are 0.13eV above 700K and 0.04eV, below 700K. At about 700K, the diffusion constants for IS and QENS have a remarkable crossover, suggesting two processes with different activation energie

Temperature dependence of the pressure-induced amorphization of ice Ih studied by high-pressure neutron diffraction to 30 K

International audienceHigh-pressure neutron diffraction allowed the in situ observation of the pressure-induced amorphization of ordinary ice Ih between 130 and 30 K, i.e., to lower temperatures than any other diffraction study before. We find that the pressure required for complete transformation into high-density amorphous ice !HDA" increases with decreasing temperature to #80 K but remains approximately constant below. Our findings support earlier evidence of two distinct mechanisms responsible for the pressure-induced amorphization in ice Ih, namely, amorphization due to mechanical melting down to lowest temperatures, and amorphization due to thermal melting at elevated temperatures. Such scenario naturally explains why HDA prepared through compression at 77 K is structurally distinct from the form of HDA obtained by the compression of low-density amorphous ice !LDA" and hence cannot be associated with the hypothesized high-density proxy of liquid water in a two-state model

The preparation and structure of salty ice VII under pressure

International audienceIt is widely accepted that ice, no matter what phase, is unable to incorporate large amounts of salt into its structure. This conclusion is based on the observation that on freezing of salt water, ice expels the salt almost entirely as brine. Here, we show that this behaviour is not an intrinsic physico-chemical property of ice phases. We demonstrate by neutron diffraction that substantial amounts of dissolved LiCl can be built homogeneously into the ice VII structure if it is produced by recrystallization of its glassy (amorphous) state under pressure. Such 'alloyed' ice VII has significantly different structural properties compared with pure ice VII, such as an 8% larger unit cell volume, 5 times larger displacement factors, an absence of a transition to an ordered ice VIII structure and plasticity. Our study suggests that there could be a whole new class of 'salty' high-pressure ice forms

Proton diffusivity in the BaZr0.9Y0.1O3−δ proton conductor

ISSN:0021-891XISSN:1572-883

Dipolar Antiferromagnetism and Quantum Criticality in LiErF4

Magnetism has been predicted to occur in systems in which dipolar interactions dominate exchange. We present neutron scattering, specific heat, and magnetic susceptibility data for LiErF4, establishing it as a model dipolar coupled antiferromagnet with planar spin anisotropy and a quantum phase transition in applied field Hc 4.0 0.1 kilo oersteds. We discovered non mean field critical scaling for the classical phase transition at the antiferromagnetic transition temperature that is consistent with the two dimensional XY h4 universality class; in accord with this, the quantum phase transition at Hc exhibits three dimensional classical behavior. The effective dimensional reduction may be a consequence of the intrinsic frustrated nature of the dipolar interaction, which strengthens the role of fluctuations