Naoyuki Fujita

Fabrication of amorphous iron-boron films by electroless plating

Abstract Amorphous iron-boron alloy films were fabricated by means of electroless plating, and the film formation mechanism was examined by studying the fabrication conditions. When a copper substrate in contact with an aluminum wire was used, the alloy films with considerably thick thicknesses were obtained. The local battery configuration of the copper substrate and the aluminum wire was considered to be responsible for the film formation. The boron content in the film increased monotonically from 0 at% to 28 at% with increasing the concentration of reducing agent (KBH 4 ). The bath temperature during the plating was found to be a significant parameter for governing the reduction power of the reducing agent and the resultant crystallographic structure of the films.

Optimum geometrical structure of highly magnetostrictive multilayer films for horizontally polarized high frequency magneto‐surface‐acoustic‐wave propagation

Optimum geometrical structure of highly magnetostrictive multilayer films for the propagation of horizontally polarized magneto‐surface‐acoustic‐wave (Love‐type MSAW) was determined theoretically. The multilayered medium is composed of highly magnetostrictive alloy films and insulating films which are stacked alternately on a glass substrate. The analysis revealed that outstanding magnetoacoustic quantities comparable to those of an ideal nonconductive medium can be realized with the conductive multilayer films whose geometrical parameters meet the following conditions: DM/DL≥1, DM/DI≥10, and N∼20, where N is the number of insulating layers having the whole thickness of DI, and DM is the whole thickness of magnetic layers. DL is a limiting thickness of the magnetic film with a single‐layer structure, above which the magnetoacoustic quantities are considerably deteriorated due to the micro‐eddy current losses.

Electrochemical deposition of amorphous FeB films with soft magnetic properties

To obtain FeB amorphous plated films with soft magnetization and high magnetostriction, effects of three kinds of agents [sodium L-ascorbate (C6H7NaO6), thiourea (NH2CSNH2), and ammonium sulfate ((NH4)2SO4)] on magnetic and magnetoelastic properties of films were investigated systematically. The first two agents, C6H7NaO6 and NH2CSNH2 were found to be ineffective for improving the soft magnetic properties of films. To the contrary, however, (NH4)2SO4 is very effective for the magnetic softening: Amorphous FeB plated films with coercivity less than 4 Oe were obtained by employing the bath composition of FeSO4⋅7H2O (71.9 mM), KBH4 (296.6 mM), NaOH (400 mM), KNaC4H4O6⋅4H2O (600 mM) and (NH4)2SO4 (80 mM). These soft films exhibited a favorable large magnetostriction of 26×10−6, being adequate for micromagnetoelastic devices.

Local detection of magneto-surface-acoustic-wave in highly magnetostrictive amorphous film by light-probing technique

we present an investigation on local properties of magneto-surface-acoustic-waves (MSAWs) propagating on Fe-Co-B amorphous sputtered films supported on soft glass substrates. The local detection of MSAW was performed by means of a light-probing technique based on the principle of Raman-Nath diffraction. The mode of MSAW in the elements was confirmed to be Rayleigh(P+SV)-type and the amplitude of MSAW was subjected to large change from place to place by applying a small field. The attenuation constant of MSAW also varied depending strongly, not only on the field strength, but also on the direction of the field relative to the direction of MSAW propagation. Theoretical analysis explains the experimental results very well in terms of the change of micro-eddy current loss in the conductive magnetic film, which reflects the change in the degree of magnetoelastic coupling in the film with external magnetic field.

Propagation characteristics of magnetoelastic surface waves in magnetic layer on non-piezoelectric substrate

The propagation characteristics of magnetoelastic surface waves in a magnetic layer on a nonpiezoelectric substrate are analyzed taking account of both thicknesses of the magnetic layer and the substrate Three fundamental modes of waves propagate in this layered structure; the extensional and the flexural modes of (P+SV)-wave and SH-wave. In these waves, the largest velocity change with external applied field appears in the flexural mode of (P+SV)-wave. The analysis reveals that the maximum velocity change has approximate squared dependence of the ratio of the magnetic layer thickness to the substrate thickness. In addition, in order to obtain large velocity change, magnetic materials are required to possess two extreme magnetic properties at the same time - very soft magnetism and very high magnetostriction.

Chemical Preparation of Zn-Incorporated Magnetite Film for High-Frequency Applications

A zinc-incorporated magnetite (Zn 0.16 Fe 2.84 O 4 ) film was fabricated on a zinc oxide (ZnO)-coated glass substrate at a deposition rate of 450 nm/h by a simple immersion in an aqueous solution containing an iron (III) nitrate hydrate and dimethylamineborane at 323 K. The structural, electrical, and magnetic characterizations were performed with X-ray diffraction, X-ray photoelectron spectroscopy, a scanning electron microscope, a two-point probe resistivity tester, a vibrating sample magnetometer, and an ultrahigh-frequency permeability measuring system. The Zn 0.16 Fe 2.84 O 4 film had a spinel cubic structure of 0.8380 nm in the unit-cell parameter and showed magnetic properties of 378 emu/cc in saturation magnetization and 39 Oe in coercive force, a very high resistivity of 5.7 × 10 6 Ω cm, and a higher permeability of around 400 at high frequencies up to 600 MHz.

Uniaxial magnetic anisotropy of amorphous Fe–B films deposited electrochemically in a magnetic field

To attempt the formation of induced uniaxial magnetic anisotropy of electrodeposited amorphous Fe–B (a-Fe–B) films, a direct current magnetic field was applied in the film plane during deposition. The easy axis of the uniaxial anisotropy was parallel to the direction of the applied magnetic field. It was found that the magnitude of the applied magnetic field necessary for the formation of induced uniaxial anisotropy is as small as 10 Oe. The composition, deposition rate, and coercivity of the films were found to be independent of the magnitude of the applied magnetic field. From scanning electron microscopy and atomic force microscopy micrographs, no topological change of the film surface due to the application of a magnetic field was observed, indicating that the anisotropy rises from a microscopic origin such as atom pair ordering as in vacuum evaporated or sputtered amorphous Fe–B films.

Diminution of Micro-Eddy-Current Losses in Magneto-Surface-Acoustic-Wave Propagation Utilizing Multilayered Magnetostrictive Film Separated by Insulating Layers

Propagation properties of the Rayleigh-type magneto-surface-acoustic-wave in multilayered magnetic alloy films were studied theoretically, where the films consisted of highly magnetostrictive layers separated by insulating layers. The analysis revealed that multilayer structure is very effective for improvement of magneto-acoustic quantities by reducing micro-eddy-current losses. We further found that the key factor in obtaining optimal conditions in the layered structure is total thickness of the insulating layers (=number of the layers × thickness of the individual layer).

BGS-type Magneto-Surface-Acoustic-Wave Devices Utilizing Horizontally Polarized PZT-Substrates

BGS-type magneto-surface-acoustic-wave(MSAW) devices were constructed by depositing highly magnetostrictive amorphous Fe-Co-B ternary alloy films by RF-sputtering on horizontally polarized PZT-substrates, since this type of MSAW is expected from our theory to have wide controllability of the propagation properties with externally applied magnetic field in comparison with those of the Rayleigh-type MSAW. We measured changes of attenuation and phase velocity as a function of magnetic field, and the results agree qualitatively with those obtained by the theoretical analysis.