Takayoshi Takeda

Magnetic Properties of the System SrCo1-xFexO3-y

Samples of the system SrCo 1- x Fe x O 3- y (0≤ x ≤1, 0≤ y ≤0.5) have been prepared under varying oxygen pressure and temperature and their crystal-lographic and magnetic properties have been studied. SrCoO 2.5 with brown-millerite type structure (high temperature phase) is an antiferromagnet with the Neel temperature of 570 K and the Co 3+ -O 2- -Co 3+ superexchange interaction is strongly antiferromagnetic. SrCoO 3 and SrCo 1- x Fe x O 3 ( x <0.9) with the cubic perovskite structure (high temperature phase) are ferromagnetic with the Curie temperature at about 200 K and the magnetization decreases rapidly with increasing x near SrFeO 3 whose magnetic structure is helical.

Magnetic Structure of Ca2Fe2O5

Magnetic measurements indicate that Ca 2 Fe 2 O 5 is an antiferromagnet, with weak parasitic ferromagnetism. The lattice, with the space group Pcmn -D 2 h 16 , can be considered as an oxygen deficient perovskite. The magnetic structure as determined from a neutron diffraction study is of G -type, and Fe 3+ spins are directed approximately along c -axis.

Magnetic properties of SrFe1-xCoxO3

Abstract Magnetic and neutron diffraction measurements have been made on the cubic perovskite-type SrFe 1- x Co x x O 3 . These oxides exhibit a helical spin configuration for 0 ⩽ x ≤ 0.1 and ferromagnetism for 0.2 ≤ x ⩽ 1. The results obtained indicate that Fe 4+ ions are nearly in a high-spin state.

Pressure and temperature effects on the phase transition from a dense droplet to a lamellar structure in a ternary microemulsion

A small-angle x-ray scattering (SAXS) study of a ternary microemulsion composed of AOT [sodium bis(2-ethylhexyl) sulfosuccinate], water and n-decane was undertaken in order to clarify the phase behavior and the feature of the corresponding structural transition from a dense droplet to a lamellar structure with increasing pressure and temperature. The volume fractions of water and decane were fixed to be equal and the volume fraction of AOT against the whole volume (φs) was selected to be 0.209 and 0.230 in order to compare results with those obtained by small-angle neutron scattering (SANS). The pressure was varied between 1 and 800 bar under controlled temperature at 20, 25, 29, or 33 °C. Under all conditions applied, the phase transition from the droplet structure to the lamellar structure was observed. The results of analysis of the SAXS profiles indicated that the short-range adhesive potential between droplets becomes more intense with increasing pressure.

A neutron spin echo spectrometer with two optimal field shape coils for neutron spin precession

Abstract We have designed and have been constructing at the C2−2 cold neutron guide port of JRR-3M, JAERI, a neutron spin echo spectrometer (NSE) which is equipped with two optimal field shape (OFS) coils for neutron spin precession with the maximum field integral of 0.22 T m, an assembly of position sensitive detectors (PSD), a converging polarizer and a wide area analyzer. The dynamic range of scattering vector Q covers from 0.005 A−1 to 0.2 A−1 and that of energy ħω from 10 neV to 30 μeV. Performance tests of the OFS coils show that the inhomogeneity of the magnetic field integral in the OFS coils with the spiral coils is so small that the NSE signal amplitude decreases little even for the neutron cross section of 30 ⊘mm diameter as the Fourier time t increases up to 25 ns, though the precession coils are close to iron covers of the neighboring neutron guide. This verifies that the OFS precession coils are appropriate for this NSE spectrometer. Another test experiment shows that the homogeneity condition of the precession magnet is loosened by use of PSD.

SAXS, SANS and NSE studies on unbound state in DPPC/water/CaCl2 system

The temperature and CaCl 2 concentration dependence of the lamellar repeat distance of a dipalmitoylphosphatidylcholine (DPPC) aqueous solution was investigated by small-angle X-ray and neutron scattering, and neutron spin echo. At certain CaCl 2 concentrations, the repeat distance in the liquid-crystalline phase tends to increase up to infinity while that in the gel phase has an upper limit. This behavior is attributable to the fact that the steric repulsion of lipid bilayers due to the membrane undulation in the liquid-crystalline phase is larger than that in the gel phase. The free-energy calculation suggested that the cooperation of the short-range electrostatic interaction and the long-range steric interaction is the origin of the increase in the repeat distance in the liquid-crystalline phase, and it can be the origin of an “unbinding transition”.

Effects of temperature and pressure on phase transitions in a ternary microemulsion system

Temperature variation experiments of small angle neutron scattering (SANS) and neutron spin echo (NSE) were carried out in order to compare effects of temperature and pressure on a structural formation in a ternary microemulsion system composed of AOT (Aerosol-OT; dioctyl sulfosuccinate sodium salt), D2O, and n-decane. From SANS measurements, a phase transition from one-phase dense water-in-oil droplet to two-phase coexistence with a lamellar and a disordered structure was observed with increasing temperature, similar to the case of pressure variation. Another phase transition was observed at a higher temperature above the lamellar phase, although such a subsequent phase transition has not been observed at higher pressure. The characteristic features of structural phase transitions by temperature and by pressure were compared by introducing a reduced temperature and pressure. The dynamical property observed from the NSE measurement was different between the high-temperature phase and the high-pressure pha...

Structural evolution and microscopic interactions in a three‐component amphiphilic microemulsion system

Structures and interaction parameters of a three‐component amphiphilic microemulsion system consisting of n‐decane, water, and an amphiphile AOT (sodium‐di‐2‐ethylhexylsulfosuccinate) have been studied by means of small angle neutron scattering. The scattering curves are fitted with Teubuer and Strey’s formula, from which three structural parameters are extracted; the average periodic distance D between the oil and water, the structural correlation length ξ, and the area aH per amphiphile molecule. The same data are further examined in terms of Gompper and Schick’s formula, from which three interaction parameters are obtained; the strength of segregation J/T among the oil and water, the amphiphilicity L/T of the amphiphile toward the oil and water, and the critical surfactant volume fraction φcs. These interaction parameters have right order of magnitudes and their implications to structural evolution are discussed.

A model of magnetic inhomogeneous structure for Fe-Ni invar alloys

Abstract The magnetic inhomogeneous structure revealed by neutron small angle scattering for Fe-Ni Invar alloys can be interpreted in terms of a model in which an effective local concentration of Fe for each atom within a sphere is taken into account in order to determine the magnetic moment of the atom.

Pressure-induced structural phase transition of dense droplet microemulsions studied by small-angle x-ray scattering

A small-angle x-ray scattering (SAXS) study of dense water-in-oil droplet microemulsions composed of water, decane, and AOT [sodium bis(2-ethylhexyl) sulfosuccinate] was performed in order to clarify phase behavior with applied pressure and the corresponding structural phase transitions. SAXS spectra were collected for pressures between ambient pressure (0.1 MPa) and 80 MPa and droplet volume fraction, φ, from 0.40 to 0.70. With increasing φ, the mean radius of droplets decreased slightly and polydispersity increased. With increasing pressure, the droplet structure transformed to a two-phase system with coexistence of lamellar and droplet structures, independent of the droplet volume fraction. These results suggest that, with increasing pressure, the increasing inter-droplet attractive force controls the pressure variation of the structure.