Akira Tasaki

Cu3N Thin Film for a New Light Recording Media

Copper nitride thin films were prepared by using the ion-assisted deposition in which accelerated nitrogen ions were irradiated during the deposition of copper metal. The degree of nitrification of the film was controlled by changing the ion current density. The reflection coefficient of the prepared copper nitride films decreased with the increase of the ion current density. The reflection coefficient was about 30% at 780 nm wavelength, and it recovered to 70% after the film was heated at 300°C. The preliminary experiment of write-once optical recording of this film was carried out, and the viability of its practical use in new media was confirmed.

Synthesis of Fine Fe4N Powder and Its Magnetic Characteristics

A pigment of Fe4N particles for magnetic recording was prepared by nitrogenizing acicular metal iron powder. The chemical treatment needed to obtain stoichiometric Fe4N powder was studied, and it was found that Fe4N powder was obtained when the Fe powder was heated at about 400°C in a mixture of H2–NH3 (65–80 vol.%). The Curie point of the powder coincided well with that of bulk Fe4N. The coercive force of Fe4N was 640 Oe, which is considerably smaller than that of the Fe powder used as the starting material. The dispersion of magnetic anisotropy was measured by a torque meter, and the decrease in the coercivity of nitrogenized iron powder was attributed to the exchange anisotropy of the surface layer.

Magnetic properties of ferromagnetic ultrafine particles prepared by vacuum evaporation on running oil substrate

Abstract Ultrafine particles of ferromagnetic metals (Fe, Co and Ni) were prepared by the vacuum evaporation onto a running oil substrate. Particles thus obtained were suspended in the oil and their average diameter was about 25 A. An electron diffraction analysis indicated that the particles were oxidized and the main component was Fe 3 O 4 , CoO and NiO for Fe, Co and Ni fine particles, respectively. From magnetic measurements in the temperature range between 4.2 and 300 K, the main magnetic behavior of the fine particles can be explained in terms of the superparamagnetism or superantiferromagnetism. Furthermore, it was concluded that the Fe 3 O 4 particles may be covered with several atomic layers of α-Fe 2 O 3 . For CoO and NiO particles, existence of an imperfect oxide structure was required besides the main components in order to explain the magnetic behavior.

Appearance of Magnetic Moments in Hyperfine Particles of Vanadium Metal

Hyperfine particles (100 to 1000 A) of vanadium were prepared by the evaporation method and the magnetic susceptibility of these fine particles was measured in the temperature range between 1.6 to 300 K. The magnetic susceptibility of these fine particles was found to consist of two parts, one was the Pauli type which was also observed in the bulk state of the metal and the other was the Curie-Weiss type overlapping the temperature independent one. The C-W component of the susceptibility increases with the decrease of particle size as the inverse of average diameter, suggesting that the magnetic moment which revealed the Curie-Weiss type susceptibility originates from the surface region of the particle. Localization of 3d-electron at the surface of particle is a probable origin of the magnetic moment.

Mechanical alloying process of Fe-Cr powders studied by magnetic measurements

A mechanical alloying process for a mixture of elemental Fe and Cr powders with the Cr compositions 20–70 at. % was investigated through the measurements of x‐ray diffraction, magnetization, and 57Fe Mossbauer spectrum. We show that magnetic studies provide more detailed information about the alloying process occurring during ball milling than the conventional diffraction techniques in this particular system. A final product after ball milling was identified as a high‐temperature phase of the α solid solution, regardless of compositions studied. Powders subjected to milling in Ar gas atmosphere for 200 h were further ball milled in N2 atmosphere. The presence of N2 gas has caused a partial amorphization. The amorphous phase thus produced is found to be paramagnetic at room temperature.

Magnetic Properties of Synthetic Single Crystal of αFe2O3

Synthetic single crystals were grown by the flux method. It was confirmed that the weak ferromagnetic moment appears only when the spins lie in the (111) plane. Contrary to the case of polycrystallines specimens, recovery of the residual magnetization or the memory phenomenon is not observed. It was found, below the transition temperature, a very small amount of the residual magnetic moment along the direction of the field during cooling. Microwave (36,000 MC/sec) resonance studies found a very small six-fold anisotropy ( K h =0.09 erg/gr.) in the (111) plane. The resonance line was easily broadened by stresses applied on the crystals. A reasonable agreement is obtained with the data of microwave studies by Abe et al., after taking into account the effect of magnetoelastic coupling. It is suggested that internal strains may induce a dominant uniaxial anisotropy in the (111) plane in polycrystals through their magnetoelastic coupling.

Axonal microtubules necessary for generation of sodium current in squid giant axons. I: Pharmacological study on sodium current and restoration of sodium current by microtubule proteins and 260K protein

SummaryEffects of the reagents suppressing or supporting axoplasmic microtubule assembly were studied on the Na ionic current of squid giant axons by perfusing the axon internally with the solution containing the reagent. Among the reagents suppressing the assembly, colchicine, vinblastine, podophyllotoxin, sulfhydryl reagents such as DTNB and NEM, and chaotropic anions such as iodide and bromide, were examined. These reagents reduced maximum Na conductance and shifted the voltage dependence of steady-state Na activation in a depolarizing direction along the voltage axis. They also made the voltage dependence less steep, but did not affect sodium inactivation appreciably. Effects on Na ionic current of reagents which support microtubule assembly (Taxol, DMSO, D2O and temperature) were opposite the effects of those agents suppressing assembly. At the same time, we demonstrated that after Na currents were partially reduced, they could be restored by internally perfusing the axon with a solution containing microtubule proteins, 260K proteins and cAMP under conditions favorable for microtubule assembly. For full restoration, it was found that the following conditions were necessary: (1) The microenvironment within the axon is suitable for microtubule assembly. (2) Tubulins incorporated into microtubules are fully tyrosinated at their C-termini. (3) A peripheral protein having a molecular weight of 260,000 daltons (260K protein) is indispensable. These results suggest that axoplasmic microtubules and 260K proteins in the structure underlying the axolemma play a role in generating Na currents in squid giant axons.

Recording tapes using iron nitride fine powder

Magnetic recording pigment of Fe 4 N particles was prepared by nitrogenizing acicular metal iron powder. The treatment to obtain stoichiometric Fe 4 N was carried out at 400°C for 3 hours in NH 3 -H 2 (3:1) mixed gas. The saturation magnetization and coercive force were 120 emu/g and 700 Oe respectively. The Curie point of the powder coincided well with that of bulk material. Test tapes were prepared with this Fe 4 N powder. The remanent magnetic flux density (Br) of the tape was 2200 G and the coercive force was 670 Oe. From test immersion in saline solution, it is confirmed that the chemical stability of the Fe 4 N tape is superior to the Fe 4 N tape is superior to the metal tape.

Magnetic properties of iron nitride thin films with high corrosion-resistance

An ion and vapor deposition (IVD), method was used to fabricate iron nitride films for use as evaporated tape media, and their film properties evaluated. In the IVD process, iron was evaporated onto a substrate that was simultaneously bombarded by nitrogen ions. The ion current density Jion was varied to investigate its effect on the deposited film. Increasing Jion led to formation of ¿-Fe2~3N over ¿-Fe, and to lower saturation magnetization and higher coercivity and squareness ratio. Iron nitride film samples showed no changes either in appearance or in magnetic properties even after exposure to a 5 percent saline solution for 300 h.

Magnetic Properties of Ferromagnetic Metal Alloy Fine Particles Prepared by Evaporation in Inert Gasses. II.

Single domain particles of Fe alloys (Fe versus Ni, Cu, Si, Cr, Gd and Ho) were prepared by the evaporation method. The saturation magnetization, remanent magnetization and coercive force of these particles were measured by an automatic magnetic balance. The dispersion of the anisotropy of Fe, Co and Ni particles were determined by a torque meter. The characteristics of these alloy particles were discussed in terms of their applicability to industrial use. The stability for oxydation and the magnetic orientation of particles have already been reported in the previous paper of this series. By choosing a suitable composition of alloys, the coercivity of the prepared particles can be controlled in the range of 200 to 1800 Oe. It was found that the anisotropy dispersion of Fe-Ni alloy was smaller than that of a commercial CrO2 tape.