Isao Nakatani

Ultramicro fabrications on Fe-Ni alloys using electron-beam writing and reactive-ion etching

A novel reactive-ion-etching (RIE) method useful for ferromagnetic material of Permalloy (80%Ni-4.5%Mo-Fe) has been developed. This method involves rf plasma of a gas mixture NH/sub 3/-CO aimed at the formation of volatile transition metal carbonyls. A maximum etching rate of 35 nm/min and highly anisotropic etching was obtained. The etching selectivity ratios of Permalloy to SiO/sub 2/ or Si were about 10 or 4, respectively. High-resolution electron-beam writing was followed by the RIE process on the Permalloy films. To achieve high-resolution electron-beam writing, amorphous carbon film was placed between the resist layer and SiO/sub 2/ film overlaid on the Permalloy film. By this method, nanostructures of Permalloy stripes of 200 nm lines and 300 nm spaces with clear-cut features were fabricated.

Iron-nitride magnetic fluids prepared by vapor-liquid reaction and their magnetic properties

Abstract A new type metallic magnetic fluids with iron-nitride ϵ−Fe 3 N fine particles dispersed in kerosene were synthesized by a method of vapor-liquid chemical reaction between iron carbonyl and ammonia. The particles are highly uniform in size and well dispersed without agglomeration. The iron-nitride magnetic fluids have high saturation magnetic flux densities up to 2330 G, and have high relative initial permeabilities up to 180. This paper presents the description on the preparative method, crystallographic properties and magnetic properties of the iron-nitride magnetic fluids.

GIANT MAGNETORESISTANCE IN GRANULAR FE-MGF2 FILMS

The giant magnetoresistance effect observed in granular Fe–MgF2 films, which consist of metallic particles embedded in an insulating medium, is reported. Large negative magnetoresistance (MR) with a magnitude up to 7.5% at 78 K was observed in semiconducting films with the Fe composition below the percolation threshold. Field dependence of the MR is well described by the form proportional to the square of the magnetization. The MR effect in this system seems to arise from the tunneling conductance between the Fe particles depending on the relative relation of the magnetization direction.

STRUCTURAL AND MAGNETIC STUDIES ON VANADIUM SPINEL MGV2O4

The magnetic properties and the crystal structure of MgV2O4 and Mg(V0.85Al0.15)2O4 have been studied. Both compounds are the normal cubic spinels with highly frustrated magnetic lattice. Around T2=65 K, MgV2O4 has magnetic orders accompanied with the cubic-tetragonal transition. Below T2, the susceptibility shows complex behavior. In Mg(V0.85Al0.15)2O4, the spin-glasslike state appears. The 51V-Knight shift of MgV2O4 has an anomalous temperature dependence, which is not simply related by that of the susceptibility.

Iron-nitride magnetic fluids prepared by plasma CVD technique and their magnetic properties

Abstract A method of preparing a new type of magnetic fluid, which contains iron-nitride fine particles dispersed in toluene, is presented. Magnetic fluids were prepared by plasma CVD reaction of Fe(CO) 5 in N 2 . The highest saturation magnetization obtained was 0.022 T. Their crystallographic and magnetic properties are discussed.

Effects of cooling field on magnetic relaxation on an iron-nitride fine particle system

Effects of the external magnetic field Ha applied during cooling on the magnetic relaxation of a fine particle system are studied. We measured the temperature decay of the residual magnetization and the ac susceptibility for frozen iron-nitride magnetic fluids. It was found that the relaxation time distribution of the diluted sample is independent of Ha and coincides with that expected from the particle diameter distribution, as the superparamagnetic model presents. On the other hand, in the concentrated sample, it is clear that the relaxation time in zero field is widely distributed and depends on Ha.

Dynamic study of iron-nitride fine particle system: field dependence of the blocking temperature

Abstract The AC susceptibility χ′ + iχ″ of frozen iron-nitride magnetic fluids was measured in static fields. The blocking temperature is estimated from the maximum of out-of-phase component χ″ against the frequency of measurement. For a diluted sample, the field dependence of the blocking temperature is explained by the Neel superparamagnetic (blocking) model for an isolated particle. For a dense sample, the blocking temperature is much higher than that for the diluted sample in a zero field and intensively decreases with the power of ⅔ of the magnetic field in the lower field range.

Curie paramagnetism of chromium ultrafine particles

Magnetic properties of ultrafine particles of chromium, 2 nm in diameter, were investigated by magnetization measurements from 4.2 K to room temperature. Observation of anomalous Curie paramagnetism with μeff=1.8 μB is reported and its possible origin is discussed.

Mössbauer studies of iron magnetic fluids prepared by evaporation method

Abstract Mossbauer spectroscopy was applied for investigating fine particles of iron contained in magnetic fluids prepared by an evaporation method. The particles are 2 nm in size and dispersed in the liquid without aggregation. The results of characterization and magnetic properties are presented. The problem of lattice vibrations in fine particles is also discussed.

The clustering phenomena of magnetic and non-magnetic particles in magnetic fluids

Magnetic fluids are suspension of ferromagnetic particles less than 10nm in diameter and it is well-known for the chain(cluster) formation of the magnetic particles under the magnetic field. In the present paper, using the light scattering from the particles, direct visualization on the behavior of cluster formation of the ferromagnetic particle and non-magnetic particles have been made under the magnetic field.