Tomoyuki Itoh

Magnetic and biomagnetic films obtained by ferrite plating in aqueous solution

Abstract Ferrite plating enables crystalline spinel ferrite films to be formed in an aqueous solution at low temperatures (less than 100°C). This technique allows the fabrication of new ferrite film devices on non-heat-resistant substrate materials such as plastics, GaAs integrated circuits ets. Ferrite-plated films prepared from aqueous solution exhibit strong compatibility with water and organic compounds which enable the films to be used in biomedical applications as biosensors and immunoassays. The low temperature synthesis of magnetite in ferrite plating bears a close analogy to the biological synthesis of magnetite in organisms such as magnetotactic bacteria and chitons.

FMR studies of spin‐spray Ni‐Zn ferrite films

Spin‐spray is a low‐temperature plating technique for which application to the growth of ferrite polycrystalline thin films on various substrates was introduced by Abe et al. a few years ago. This technique is particularly attractive because of the possibility it offers for integrating ferrite devices with GaAs microwave monolithic integrated circuits, since growth occurs at temperatures on the order of 90 °C. In particular, the growth of Ni‐Zn ferrite films has been demonstrated and these films could be used to build microwave nonreciprocal devices such as isolators and circulators. In order to understand and utilize the microwave magnetic properties of these films, a study of their ferromagnetic resonance (FMR) characteristics, as a function of composition and growth conditions, has been conducted. Important parameters such as saturation magnetization, FMR linewidth, and gyromagnetic ratio were calculated from the data obtained. Compositional and structural nonuniformities were also revealed in the anal...

Ferrite‐organic multilayer film for microwave monolithic integrate circuits prepared by ferrite plating based on the spray‐spin‐coating method

We have made multilayer films in which NiZn‐ferrite (Fe2.70±0.04‐Ni0.14±0.03 Zn0.14±0.03O4) layers (2000–8000 A thick) and dextran [(C6H10O5)1200–1800] buffer layers (100 A thick) are laminated alternately on a glass substrate. The ferrite layers were formed by ferrite plating based on the spray‐spin‐coating method at 80 °C, compatible with the low heat resistance (∼300 °C) of GaAs microwave monolithic integrated circuits. To enhance the adhesive power of the multilayer film, thin (∼300 A) magnetite layers were deposited intermediate between the NiZn‐ferrite and dextran and also between the NiZn‐ferrite and the substrate. The grain growth in the ferrite layers is interrupted at the dextran buffer layers, which release the stress induced in the ferrite layers. Thus the multilayer film can grow much thicker (i.e., up to ∼5 μm) than a NiZn‐ferrite monolayer film which peels off at ∼1.5 μm thickness due to the stress. In the multilayer films, the ferrite layers are of polycrystalline spinel structure having n...

High-Rate Deposition of Ferrite Films in Aqueous Solution by Light-Enhanced Ferrite Plating

By irradiating the substrate surface with a Xe-lamp at 450 W/cm2, the deposition rate of Fe3O4 film in ferrite plating was increased by a factor of 10 (from ~30 nm/min to ~320 nm/min). The high deposition rate in light-enhanced ferrite plating cannot be simply ascribed to the increase of thermal energy.

Ultrasonic Visualization of Still and Flowing Waters Using Contrast Agents of Magnetite-Encapsulated Porous Silica Microspheres

Porous silica microspheres, ~2.2 µm in average diameter, were encapsulated with magnetite ( Fe3O4) by ferrite plating in an aqueous solution of FeCl2 at 65°C. Using the resultant ferrite-encapsulated particles as ultrasonographic contrast agents (in which air trapped in the pores scatters ultrasonic waves), we tried to visualize still and flowing waters in holes and a channel perforated in agar blocks using a 7.5 MHz B-mode echograph. Clear image enhancement was successfully obtained only when the ferrite-encapsulated particles were evaporated before they were dispersed in the water. This is because during ferrite plating in the aqueous solution the pores were permeated with water, which was expelled by evaporation, and then substituted by air when the particles were again exposed to air.

The magnetic and structural properties of ferrite plated NiZn-ferrite films

Magnetization, magnetic anisotropy and ferrimagnetic resonance linewidth measurements have been made on a series of NiZn-ferrite films synthesized using a low temperature (T >

Preparation and Application of Magnetic Films by Ferrite Plating in Aqueous Solution

Ferrite plating invented by the authors facilitates formation of crystalline films of spinel, (Fe, M) 3 O 4 (M=Fe, Ni, Co, Mn, Zn, etc.), in an aqueous solution below 100 °C. This opened the door to new ferrite-film devices which use, as substrate, such non-heat-resistant materials as plastics and GaAs ICs. In this paper we describe the principle and the experimental methods of ferrite plating and report magnetic and structural properties of the films. We also describe various applications of the ferrite plating films to microwave, electrochemical and bio-medical devices.

Ferrite formation in aqueous solution at 100-200°C

Abstract The formation of Fe 3 O 4 and Ni(II)-ferrite films by oxidation of Fe(II) in aqueous solution was studied in the temperature range 100–200°C. To make it possible to perform the study, a special piece of equipment was designed with two high-pressure pumps, which could introduce the aqueous solutions of Fe(II) ions and the oxidizing agent (NaNO 2 ) into a reaction cell at a high pressure (10 5 −2 × 10 6 Pa). Fe 3 O 4 was obtained below 120°C for pH above 5.5, but two products of Fe 3 O 4 and α-Fe 2 O 3 were obtained above 120°C. For the reaction solution containing Fe(II) and Ni(II) ions, only the Ni(II)-ferrites appeared in the temperature range 100–200°C, where the two products of Fe 3 O 4 and α-Fe 2 O 3 appeared for the reaction solution containing only the Fe(II) ion. The Ni(II) content in the Ni(II)-ferrite increased with an increase in Ni(II) concentration in the reaction solution and/or with temperature.

Maskless Patterning of Ferrite Film by Selected Area Film Growth in Aqueous Solution by “Laser-Enhanced Ferrite Plating”

By irradiating substrate with Ar-laser (λ=514.5 nm) beams, Fe3O4 films were deposited in an aqueous solution at a rate as high as ~660 nm/min. By synchronously moving the substrate during the plating process, we successfully drew letters of ferrite film patterned on a glass substrate by selected area growth without using any masks. This technique is useful for fabricating fine-patterned ferrite film devices (e.g., microwave circulators and isolators) using as a substrate such non-heat-resistant materials as GaAs ICs.

Preparation of CoxFe3-xO4 Films in Aqueous Solution at 120-200°C by “Hydrothermal Ferrite Plating”

By a hydrothermal ferrite plating method, we synthesized Fe3-xCoxO4 (x=0~1.3) films at temperatures of 90~180°C and pressures of 15~40 kg/cm2. The solubility limit of Co increases as temperature increases, from x=~0.6 at 90°C to x=1.3 at 180°C. All of the films are polycrystalline with no preferential orientation, and the magnetization lies in the film plane. The magnitudes of the saturation magnetization of the films are smaller than those expected for bulk samples, probably because 1) Co2+ ions are oxidized to Co3+ in a nonmagnetic low spin state, and the concentration of Co3+ in the film is higher than that in bulk samples owing to strong oxidizing activity, or 2) nonmagnetic impurity phases exist in the film. The highest value of the coercive force is obtained for films of Fe1.7Co1.3O4 synthesized at 180°C, and reaches ~1300 Oe.