Nobuhiko Wada

Magnetic Properties of Ferromagnetic Metal Fine Particles Prepared by Evaporation in Argon Gas

Fine particles of Fe, Co and Ni were prepared by evaporation in the atmosphere of argon gas at low pressure. The diameters of the particles ranged from about 100 A to 2000 A. Magnetization of particles was measured by magnetic balance. For Fe and Co the saturation magnetization of the finest and the most coarse particles were about 20 per cent and 90 per cent of those of bulk metals, respectively. For Ni, it was more than 80 per cent and the particle size dependence was less than for Fe and Co. The remanent magnetization and the coercive force were largest for the particle diameter of 300 A of Fe and Co. The effect of superparamagnetism for smaller particles was not observed. When deposited in magnetic field, long chains of particles appeared along the field direction. Such specimens showed hysteresis curves much more convex than that of randomly oriented ones and remanent magnetization twice as large.

Preparation of Fine Metal Particles by Means of Evaporation in Xenon Gas

Fine particles of Mg, Zn, Cd, Al, Fe, Cu and Ag were prepared by means of evaporation in helium gas. Compared with those prepared in argon gas (Japan. J. appl. Phys. 2 (1963) 702), the particle size was much smaller, provided the pressure was the same. To obtain the same size, the pressure of helium had to be about ten times as large as that of argon.

Nuclear Fusion in Solid

Spontaneous neutron emissions were intermittently detected from activated palladium rods well soaked with deuterium gas in a closed glass bulb. By the stimulation of the palladium rods with a high voltage discharge between the rods, a burst of neutron flux 2×104 times larger than background was detected. Atoms or molecules of mass number 1, 2, 3, 4, 5 and 6 were found in the residual gas. Nuclear fusion in solid is interpreted in terms of the supersaturation of the solid solution of deuterium.

Magnetic Properties of Ferromagnetic Metal Alloy Fine Particles Prepared by Evaporation in Inert Gases

Single domain fine particles about 150 A in diameter, of alloys of Fe, Co and Ni were prepared by evaporation in an atmosphere of argon at 3 Torr. The particles were coupled with each other like a necklace. The X-ray diffraction analysis revealed that the lattice parameters of the alloy particles agreed with those of the original bulk alloys within an experimental error of 0.3%. It was indicated, however, that they might be smaller than the latter within that error. The maximum coercive force observed in Fe–Co alloys was about 1.5 kOe. It was found that the oxidation of Fe–Co alloys can be prevented by adding some Ni. The magnetic orientation of particles caused by application of a magnetic field during the evaporation was studied. In a magnetic field of 0.5 kOe the necklace structure was aligned parallel to the field and a magnetic anisotropy of 3.5×105 erg/g appeared in this oriented sample. This strong anisotropy is considered to be due to a shape anisotropy induced by alignment.

Preparation of Fine Metal Particles by the Gas Evaporation Method with Plasma Jet Flame

Fine particles prepared by means of evaporation in inert gas have been expected to show various interesting physical or chemical properties, By the conventional method of heating by tungsten wire, only ten milligrams of particles were produced in one cycle of evaporation. In the present experiment a plasma jet flame with helium gas is used for heating and a gram of particles were produced in five minutes continuously. The produced particles of Fe-Co-Ni alloy are examined by electron-microscope and a X-ray diffractometer. The crystal structure, oxidation, lattice imperfection and sizes of the particles are discussed.

A Method of Preparation of Finely Dispersed Ultrafine Particles

A method was developed for preparing finely dispersed ultrafine particles by means of gas or vacuum evaporation onto frozen surfaces of various solvents. Fine particles of Ni, Ag, Cu, Au, Sb and Al with the size 20A~120 A could be prepared in some organic solvents.

Synthesis of Coesite from Ultra Fine Particles

Coesite, a high pressure phase of SiO2, was synthesized without H2O or any other catalizing component at temperatures as low as 250°C from ultra fine particles (80 A in diameter) of silica produced by the gas evaporation technique. The ultra fine particles were worked by a tetrahedral anvil type high pressure apparatus up to a pressure of 50 kbar at 450°C for 30 minutes and almost 100% of the particles were crystallized into coesite. Mechanically ground quartz and silica-gel of a few µm in size were also worked under the same condition. The reaction speed of recrystallization of the ultra fine particles was roughly estimated to be ten times or more that of particles of micron size.

Electron Spin Resonance in Fine Particles of Metallic Lithium

Fine particles of metallic lithium of diameters from about 3000 to 100A were prepared by the evaporation method in an inert gas atmosphere. The relaxation of conduction electron spins in those particles was measured by an X-band spectrometer at room temperature. The line of the electron spin resonance broadened from 2.7 to 8.2 Oe as the particle size was reduced from about 3000 to 1000A. This effect is explained by the spin reverse scattering at the surface of the particles. As the particle size was further reduced, the line narrowed remarkably. The width for 100A particles was 1.9 Oe. This effect is discussed in connection with the quantization of electronic energy levels in fine particles. The measurement was also carried out at liquid helium temperature. However, on remarkable change was observed.

An EXAFS Investigation on the Lattice Relaxation of Ni-Fine Particles Prepared by Gas Evaporation

EXAFS measurements were made on Ni-fine particles (14–5 nm in size) prepared by the gas evaporation technique. Data were analysed by the fine adjustment method developed by Teo et al. Substantial lattice relaxation shows an increase in the nearest Ni-Ni bond distance (R1), a decrease in the coordination number (N1) and an increase in the Debye-Waller factor (σ1). These facts can be explained as a result of the chemisorption of oxygen on the surface of fine particles.

D.C. Electric Conductivity in Films of Aluminum Fine Particles Prepared by Evaporation in Helium Gas

It was reported in a previous paper that aluminum granular films prepared by means of gas evaporation in helium showed enhanced superconductivity. In the present experiment, a temperature dependence of D. C. electrical resistivities of these films is measured by means of a four contact method. It is found that absolute values of the resistance depend on the film thickness but the most of the films show temperature independent resistivity. These features are interpreted in terms of electronic mean free path and the particle size of the films.