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Sugiyama J.,Toyota Central R&D Labs. | Mansson M.,ETH Zurich | Ofer O.,TRIUMF Laboratory Particle and Nuclear Physics | Kamazawa K.,Toyota Central R&D Labs. | And 11 more authors.
Physical Review B - Condensed Matter and Materials Physics

The presence of antiferromagnetic (AF) order seems to be a common feature for the parent compounds of cuprate as well as some pnictide high-temperature superconductors. In order to search for antiferromagnetic order in the closely related rare-earth cobalt arsenic oxides (RCoAsO), we have measured muon-spin rotation and relaxation (μ+SR) spectra on a series of powder samples with R=La, Ce, Pr, Nd, Sm, and Gd. It was found that, besides GdCoAsO, all the other five compounds enter into a static ferromagnetic ordered phase below around 70 K (=TC), while additional transitions into a static AF ordered phase were found for NdCoAsO and SmCoAsO. For GdCoAsO, a static ferrimagnetic phase appeared below 60.5 K and then an incommensurate spin-density-wave ordered phase followed below 3.2 K. The AF spin structure was also found to strongly depend on R. © 2011 American Physical Society. Source

Nozaki H.,Toyota Central RandD Laboratories Inc. | Mansson M.,Paul Scherrer Institute | Roessli B.,Paul Scherrer Institute | Pomjakushin V.,Paul Scherrer Institute | And 10 more authors.
Journal of Physics Condensed Matter

The magnetic structure of the metallic antiferromagnet Ag 2NiO2 with the Néel temperature TN = 56 K has been investigated by means of a neutron diffraction technique using a powder sample in the temperature range between 5 and 65 K. The antiferromagnetic (AF) diffraction peaks are clearly observed below TN and can be indexed with the propagation vector . Based on the results of both a representational analysis and a Rietveld refinement of the magnetic peaks, the AF spin structure is determined as an A-type AF structure with ml = m0cos(2πk ṡl), where ml is the moment at the lth Ni3+ site and m0 = (0.31,0,0.65) μB at 5 K. © 2013 IOP Publishing Ltd. Source

Medarde M.,Paul Scherrer Institute | Mena M.,Paul Scherrer Institute | Gavilano J.L.,Paul Scherrer Institute | Pomjakushina E.,Paul Scherrer Institute | And 9 more authors.
Physical Review Letters

We report the observation of a stepwise "melting" of the low-temperature Na-vacancy order in the layered transition-metal oxide Na 0.7CoO2. High-resolution neutron powder diffraction analysis indicates the existence of two first-order structural transitions, one at T1≈290 K followed by a second at T2≈400 K. Detailed analysis strongly suggests that both transitions are linked to changes in the Na mobility. Our data are consistent with a two-step disappearance of Na-vacancy order through the successive opening of first quasi-1D (T 1>T>T2) and then 2D (T>T2) Na diffusion paths. These results shed new light on previous, seemingly incompatible, experimental interpretations regarding the relationship between Na-vacancy order and Na dynamics in this material. They also represent an important step towards the tuning of physical properties and the design of tailored functional materials through an improved control and understanding of ionic diffusion. © 2013 American Physical Society. Source

Sugiyama J.,Toyota Central R&D Labs. | Nozaki H.,Toyota Central R&D Labs. | Harada M.,Toyota Central R&D Labs. | Kamazawa K.,Toyota Central R&D Labs. | And 9 more authors.
Physical Review B - Condensed Matter and Materials Physics

In order to study the diffusive nature of lithium transition-metal phospho-olivines, we measured muon-spin relaxation (μ +SR) spectra for the polycrystalline LiMPO 4 samples with M=Mn, Fe, Co, or Ni in the temperature range between 50 and 500 K. The μ +SR spectra under zero applied field are strongly affected by the magnetic moments of the 3d electrons in the M2 + ions so that, for LiMnPO 4, it was difficult to detect the relaxation change caused by the diffusion due to the large Mn2 +(S=5/2) moments. However, diffusive behavior was clearly observed via the relaxation due to nuclear dipolar fields above ∼150 K for LiFePO 4, LiCoPO 4, and LiNiPO 4 as S decreased from 2 to 1. From the temperature dependence of the nuclear field fluctuation rate, self-diffusion coefficients of Li + ions (D Li) at 300 K and its activation energy (E a) were estimated, respectively, as ∼3.6(2)×10 -10 cm2/s and E a=0.10(2) eV for LiFePO 4, ∼1.6(1)×10 -10 cm2/s and E a=0.10(1) eV for LiCoPO 4, and ∼2.7(4)×10 -10 cm2/s and E a=0.17(2) eV for LiNiPO 4, assuming that the diffusing Li + ions jump between the regular site and interstitial sites. © 2012 American Physical Society. Source

Nyuta K.,Tokyo University of Science | Yoshimura T.,Nara Womens University | Tsuchiya K.,Tokyo University of Science | Sakai H.,Tokyo University of Science | And 3 more authors.
Journal of Colloid and Interface Science

The aggregation behavior in aqueous solution of zwitterionic heterogemini surfactants, N,N-dimethyl-N-[2-(N'-alkyl-N'-β-carboxypropanoylamino)ethyl]-1-alkylammonium bromides (2C nAmCa, in which n represents hydrocarbon chain lengths of 8, 10, 12, and 14), with nonidentical headgroups containing ammonium and carboxylate was investigated through small-angle neutron scattering (SANS), dynamic light scattering (DLS), and cryogenic transmission electron microscopy (cryo-TEM) techniques. We found that the aggregation behavior of 2C nAmCa strongly depended on the hydrocarbon chain length and the surfactant concentration. 2C 8AmCa forms spherical micelles with radius of approximately 2nm in solution. 2C 10AmCa forms rod-like micelles at low concentration in the solution, and the structure changes to vesicles with increasing concentration. The membrane thickness of the vesicle is independent of the surfactant concentration. Aggregation shape transitions were also observed for 2C 12AmCa. In addition, it appears that the vesicles of 2C 12AmCa coexist with the rod-like micelles at a wide range of surfactant concentrations. Interestingly, 2C 14AmCa forms vesicles with averaged membrane thickness of 2.32nm in solution, even at the extremely low concentration of 10 times the cmc. Thus, it was concluded that 2C nAmCa exhibits unique aggregation behavior, such as the formation of spherical micelle→rod-like micelle→rod-like micelle+vesicle (coexistence)→vesicle with increasing hydrocarbon chain length and surfactant concentration. We also found that the membrane structure is an interdigitated bilayer when the vesicles are formed. This formation of interdigitated structures is related to the origins of the effective properties of 2C nAmCa in solution. © 2011 Elsevier Inc. Source

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