T. Itoh

Light‐enhanced ferrite plating of Fe3−xMxO4 (M=Ni, Zn, Co, and Mn) films in an aqueous solution (invited)

Polycrystalline spinel ferrite films were plated on glass substrates in an aqueous solution by the thin liquid‐film method combined with an electric lamp, which was named ‘‘light‐enhanced ferrite plating.’’ By irradiating the substrate surface with a Xe lamp (450 W/cm2), the deposition rate of Fe3O4 films increased by a factor of ∼5–10 (from 30 to 150–320 nm/min) compared to that obtained without the light irradiation. The Fe3O4 film prepared in a reaction solution with a small FeCl2 concentration had a structure (i.e., grain size ∼200 nm, and columnar structure perpendicular to the film surface) similar to that observed when prepared without the light irradiation. However, the grain size increased and the columnar structure disappeared as the FeCl2 concentration increased. The deposition rate of Fe3−xMxO4 (M=Ni, Mn, Co, and Zn) was 50–100 nm/min and increased by a factor of 2–5 compared to that without the light irradiation. The saturation magnetization of the all films prepared with the light irradiatio...

Ferrite plating of Fe/sub 3/O/sub 4/ and Fe/sub 3-x/Ni/sub x/O/sub 4/ films at 100-200 degrees C

Ferrite plating of Fe/sub 3-x/Ni/sub x/O/sub 4/ (x=0-0.93) films in the temperature region T=120 degrees C-200 degrees C and in the pressure region P=15-20 kg/cm/sup 2/ was performed. A reaction solution and an oxidizing solution were supplied to a reaction cell by high-pressure pumps. A phase diagram for an iron oxide film was obtained for T=120 degrees C-180 degrees C and pH=4.0-7.6. Single-phase Fe/sub 3/O/sub 4/ (x=0) film grows only at T=180 degrees C and pH=6.0-7.6, with the alpha -Fe/sub 2/O/sub 3/ phase appearing outside the region. The solubility limit of Ni increases as the plating temperature increases, from x= approximately 0.3 at 80 degrees C to x=0.93 at 200 degrees C. All the films are polycrystalline with no preferential orientation, and the magnetization exhibits no definite anisotropy. The grain size of the films increases as x increases, reaching approximately 1 mu m at x=0.86. >

Preparation of NiZn ferrite films by spin‐spray ferrite plating on oxygen‐plasma‐treated substrates

Polycrystalline NixZnyFe3−x−yO4 films were prepared by the spin‐spray ferrite plating method on oxygen‐plasma‐treated and non‐plasma‐treated glass substrates from an aqueous solution at 96 °C. The oxygen‐plasma treatment increased film adhesion to the substrate, and enabled films thicker than 15 μm to be grown. A film with composition of (x+y)=0.75 had a saturation magnetization of 103 emu/g, a coercive force of ∼7 (Oe), ferromagnetic resonance linewidth (perpendicular to the film plane) of 80 (Oe), and resistivity of 106 Ω cm. These results compare favorably with ceramics of NiZn ferrite on the market.

Magnetite coating prepared by ferrite plating on expanded polytetrafluoroethylene membrane for medical use

As the first step to the study of increasing biocompatibility of expanded polytetrafluoroethylene (EPTFE) membranes, cardiovascular patches of EPTFE substrates were coated with Fe3O4 layer, which is expected to accelerate proliferation of endothelial cells. The ferrite layers were formed by the thin liquid film ferrite plating method at T=75–90 °C and pH (in oxidizing solution)=6.9–7.4. At a fixed pH value, a single‐phase Fe3O4 layer is obtained when T is higher than a threshold temperature, which increases with an increasing pH value; below the threshold temperature, the layer has an impurity phase of γ‐FeOOH. The obtained Fe3O4 layers are polycrystalline with no preferred orientation, having magnetization and coercive force which agree with those reported for bulk samples.

Ferrite plating of Fe/sub 3/O/sub 4/ films using alternate electric current

Magnetite (Fe/sub 3/O/sub 4/) films were synthesized at 95/spl deg/C on Au and stainless steel substrate from an aqueous solution (pH=/spl sim/6.8) of FeSO/sub 4/ by conducting ac current (Vp-p=1/spl sim/40 V, f=10 Hz/spl sim/100 kHz) between the substrate and a Pt electrode. The deposition rate increased from /spl sim/8 nm/min to /spl sim/18 nm/min as the frequency of the current increased from 10 Hz to 100 kHz. The films were polycrystalline having magnetic properties favorably compared to those of bulk Fe/sub 3/O/sub 4/. >

High‐vacancy‐content ferrite with fine particles

The high‐vacancy‐content ferrites represented by x(MFe2O4)⋅y(Fe3O4)⋅z(γ‐Fe2O3), where x+y+z=1 (z≳0.50), were obtained in the clear and strongly alkaline solutions of Fe(III) and M(II) tartrate [M(II)=Zn(II), Ni(II), and Cd(II)] or dextrose at 100 °C. The vacancies were replaced with the bivalent metal ions in the reaction solutions, and the replaced number increased with an increase in the concentration of the bivalent metal ions. The ferrite particle size was dependent on the bivalent metal species and the content (x,y). The Fe(II) ions enhanced the crystal‐growth rate. The particle size of the magnetites (x=0) increased from 100 to 800 A with an increase in the Fe(II) ion content (y=0.10–0.35). The high‐vacancy‐content magnetite was transferred from superparamagnetic to ferrimagnetic particles as the size increased. The Zn(II), Ni(II), and Cd(II) ions did not enhance the growth rate so much as compared to the Fe(II) ions. The particle sizes were less than 200 A, and most of the particles were superparam...

Preparation of CoxFe3−xO4 films in aqueous solution at 120–200 °C by ‘‘hydrothermal ferrite plating’’ (abstract)

Ferrite plating facilitates the formation of polycrystalline spinel films in an aqueous solution below 100 °C. The plating temperature can be extended up to 200 °C when the pressure of the reaction solution is kept high (15–20 kgf/cm2). We call this ‘‘hydrothermal ferrite plating,’’ by which solubility limit of Ni in Fe3−xNixO4 increases much, from x=0.3 (by conventional ferrite plating at 90 °C) to x=0.93.1 In this paper we describe preparation of Fe3−xCoxO4 films by the hydrothermal ferrite plating at T=120–200 °C and p=15–40 kgf/cm2, and report their structural and magnetic properties. Plating for 1 h, we obtained films about 1 μm in thickness, which are polycrystalline with no preferential crystal orientation as observed by x‐ray diffraction. The solubility limit of Co, which is x=0.6 at 90 °C, increases to x=1.3 at 180 °C. The solubility limit of Co is higher than that of Ni, which may be because Ni tends to keep 2+ state in the spinel structure, while Co can take both 2+ and 3+ states. When prepared...

Preparation of Fe 3 O 4 Films by Light-Enhanced Ferrite Planing

Polycrystalline Fe3O4 films were plated on glass substrates in an aqueous solution. By irradiating the substrate surface with an Xe lamp at power density of ~450 W/cm2, the deposition rate of Fe3O4 film was increased by a factor of about 10 (from ~30 nm/min to ~320 nm/min). With light irradiation times as short as 4 min, we obtained ferrite films of ~2 ¿m thickness. We believe that the light accelerates the reaction by raising the temperature. X-ray analysis revealed that the films were polycrystalline with a spinel structure, with no preferred orientation, and no scattering due to impurity phases was observed.

Microwave dielectric loss reduction by vacuum treatment for (Ni,Zn,Fe)/sub 3/O/sub 4/ films prepared by ferrite plating

Films (/spl sim/0.5 /spl mu/m thick) of Ni/sub 0.3/Zn/sub 0.4/Fe/sub 2.3/O/sub 4/ were deposited on BN substrates by spin spray ferrite plating from an aqueous solution at 97/spl deg/C. Exposing the films to vacuum (/spl sim/0.01 Torr) for 5 hrs at room temperature reduced their dielectric losses, tan/spl delta/, from /spl sim/0.005 (including losses in the BN substrates) to /spl sim/0.002, a value which is indistinguishable from the loss in the substrates. Annealing the films at 300/spl deg/C in air for 2 hrs also decreased the losses in a similar way, which, however, deteriorated the magnetic characteristics (saturation magnetization, coercive force, and FMR line width) of the films. On the contrary, the vacuum treatment did not deteriorate the magnetic properties at all. The dielectric loss was improved probably because the OH group trapped in the films from the aqueous solution were desorbed by the vacuum or the heat.

Catalytic‐active ferrite plating films with Au particles dispersed

We prepared ferrite films of Fe3O4 and α‐Fe2O3 in which Au fine particles (which exhibit catalytic activity for CO→CO2 oxidation) are dispersed by ferrite plating in an aqueous solutions below 100 °C. We used as‐reaction solution FeCl2 (Fe2+ + Cl−) and as oxidizing solution HAuCl4 (H+ + AuCl−4). The reduction‐oxidation reaction between Fe2+ and AuCl−4 facilitates the ferrite formation and also Au‐particle formation reactions. The Au particles were ∼30 nm in diameter. Among all the prepared films an α‐Fe2O3 film containing Au fine particles at an atomic ratio Au/Fe=0.12 exhibited the highest oxidation activity, which appeared above 100 °C, and converted the CO gas to CO2 completely at 200 °C.