Hisashi Sekizawa

Angular Distribution of Positron Annihilation Radiation in Vanadium and Niobium–Experiment

Angular distributions of two photons resulted from annihilation of positrons in V and Nb were measured along three principal crystallographic directions and conspicuous structures and anisotropies ...

On the Reduction in Magnetization by Clod Working on the Ferromagnetic Heusler Alloy Pd2MnSn

Results are presented of X ray, magnetic and the Mossbauer effect measurements on cold worked Pd 2 MnSn which shows a remarkable reduction in magnetization. Most of the reduced magnetization is recovered when the strain is released by annealing of the specimen at temperatures below 400°C, where no appreciable recovery of the chemical order takes place. This fact means that the reduction in magnetization is related to the severely stressed state rather than to the atomic order.

Angular Correlation of Positron Annihilation Radiation in Chromium and Molybdenum

Angular correlation of positron annihilation radiation in Cr and Mo were measured. Self-consistent band structure calculations for Mo were carried out by the APW method with state-dependent potentials. Theoretical angular correlations for Cr and Mo were also calculated by the APW method. Observed fine structures on the angular correlations and the crystalline anisotropies were well reproduced by the calculations. However, when the theoretical and experimental correlation curves were normalized to an equal area, the theoretical curves were consistently lower in counting rate than the experimental ones in small angle region, and higher in large angle region. This type of discrepancy between the theory and the experiment is the same as we previously found in V and Nb, and is ascribed to the electron-positron correlation effects.

Electrons and Positrons in Amorphous Mg70Zn30

Measurements of the Compton profiles and angular correlations of positron annihilation radiations on the amorphous Mg 70 Zn 30 alloy are carried out. From the Compton profile measurement it is found that the valence electrons are free-electron like and the Fermi momentum is 0.77 ±0.02 atomic units ( k F =1.46 ±0.02 A -1 ) in agreement with the value calculated from a simple electron gas model. The angular correlations of positron annihilation radiations measured at 80 K and 300 K show significant smearing of the break at the Fermi momentum. The smearing at 80 K is heavier than that at 300 K. The smearing is found to be caused by localization of the positron. The potential for localization of the positron is much shallower and wider than that due to a vacancy in crystalline materials. The positrons are localized in low density dilated regions of the amorphous structure.

Interligand interactions affecting specific metal bonding to nucleic acid bases: X-ray crystal structure of tetrakis-µ-acetamidatobis(theophylline)rhodium(II)-rhodium(III) nitrate monohydrate

X-Ray crystal structure analysis of tetrakis-µ-acetamidatobis(theophylline)rhodium(II)-rhodium(III) nitrate monohydrate, an adduct produced by oxidation with nitric acid, has shown that the dirhodium-tetra-acetamidato nucleus is occupied at the two axial positions by the N(7) site of the theophylline base; interligand hydrogen bond formation between the acetamidate nitrogen and the exocyclic oxygen O(6) of the base is an important factor favouring metal bonding to the N(7) site.

Experimental Compton Profiles of Magnesium

Directional Compton profiles for magnesium single crystals are measured using 60 keV γ rays, and are compared with the theoretical profiles calculated by the APW method. Good agreement is found between the experimental and the theoretical Compton profiles. However, the conduction electron part of the experimental Compton profile is slightly broader than that of the theoretical one. A reason for this broadening is discussed by considering non-constant occupation probability of the conduction electrons caused by the electron-electron correlation. No crystalline anisotropy of the experimental directional profiles is found, being consistent with the theoretical results.

Angular Distribution of Positron Annihilation Radiation in Aluminum—Experiment

Angular distributions of two photons resulted from annihilation of positrons in Al were measured along three principal crystallographic directions. The observed distribution curves were compared with the results of the APW calculation by Kubo et al. The fine structures and the anisotropies of the experimental curves verified theoretical predictions and were interpreted in terms of the shapes of the Fermi surfaces. A slight discrepancy that the theoretical curves were a little narrower than the experimental ones in the main part of the curves was found. This discrepancy is ascribed to the effect of the positron-electron interaction. By introducing enhancement factors much better agreement has been attained.

Dependence on Heat-treatment of the Ferromagnetic Resonance Width in Ni Ferrite

The ferromagnetic resonance absorption in Ni ferrite is observed at 9300 MC. The single crystal specimen is prepared by PbO flux method, and has the composition Ni 0.96 Fe 2.04 O 4 . The experiments are made repeatedly on one and the same specimen after various heat-treatments. The width, anisotropy constants, and g -factor change appreciably by the treatments. The results can be accounted for qualitatively to some extent, as caused by the change in the spinel phase itself or by the effect of precipitation. The minimum width obtained of 15 Oe is far narrower than that reported previously for the ferrites.

Loss Processes of N2(A3Σ+u) in N2+CO Mixture Gases

Previously, we investigated the destruction processes of metastable nitrogen molecules N 2 (A 3 Σ u + ), and analyzed the experimental data by taking the reflection of metastables at the boundary into account. In this paper, the work is extended to N 2 +CO mixture gases in order to investigate the influence of added CO on N 2 (A 3 Σ u + ). In the low pressure region, the experimentally obtained effective lifetime τ 1 of N 2 (A 3 Σ u + ) decreases only slightly with an increase in CO content. On the other hand, the reflection coefficient of N 2 (A 3 Σ u + ) on the electrode surface seems to become smaller by adding CO molecules, although scattering of the measured values are appreciable.

Effect of pressure on the Néel temperature of rare earth intermetallic compounds

Abstract The pressure coefficient of the Neel temperature and the compressibility were obtained on two rare earth intermetallic compounds. Samples studied were GdCu and GdAg which have the CsCl type of crystal structure and show antiferromagnetic property at low temperature. The Neel temperature was determined by the abrupt change in the slope of the electrical resistivity vs. temperature curve. The resistivity was measured on polycrystalline samples over the temperature range from 77° to 200°K at a constant hydrostatic pressure. Pressures up to 5 kbar were employed. The Neel temperature was found to increase linearly with pressure at a rate of 0.03 ± 0.04°K/kbar for GdCu and 0.43 ± 0.04°K/kbar for GdAg. Volume compressibilities at room temperature are 2.2 × 10 −3 /kbar and 2.0 × 10 −3 /kbar for GdCu and GdAg, respectively. Values of d lnT N /d lnV are −0.09 for GdCu and −1.6 for GdAg.