Y. Shimada

Microfabrication and characteristics of magnetic thin-film inductors in the ultrahigh frequency region

Thin-film inductors for 1 GHz-drive mobile communication handset application has been demonstrated. This is the possible practical application of soft magnetic films in 1 GHz range. Fe61Al13O26 with Ms=1.2 T, ρ=500 μΩ cm, fr=2 GHz were used for the inductors. L=7.6 nH, R=6.5 Ω, and Q=7.4 were obtained at 1 GHz in a 370 μm×370 μm square four turn spiral of line/space=11 μm/11 μm covered with 0.1-μm-thick slitted Fe61Al13O26 film with Cr underlayer. The L was increased over the flux saturated inductor by 8.6% without any degrade of quality factor.

Conducted noise suppression effect up to 3 GHz by NiZn ferrite film plated at 90 °C directly onto printed circuit board

A NiZn ferrite film (3 μm thick) was deposited at 90 °C by the spin-spray ferrite plating from an aqueous solution onto a 50 Ω microstrip line formed on an epoxy printed circuit board (PCB). A strong magnetic loss was caused by the ferrite film in a GHz range, ΔPloss reaching 67% attenuation at 3 GHz, the upper limit of our measurement. Furthermore, the reflection loss was very weak, S11 being smaller than 7%. Thus plated NiZn ferrite films hold strong promise to be actually applied to a type of thin film electromagnetic noise suppressors; the films can be directly deposited onto noise sources (semiconductor elements or electronic circuits) to attenuate conducted-electromagnetic noises in the GHz range. Because the plated NiZn ferrite film was magnetically isotropic in film plane, the noise suppressors will be isotropic, attenuating noise electromagnetic waves radiated from any directions. The NiZn ferrite film was also plated on a flat glass substrate as a standard, which exhibited natural resonance freq...

Sensitive detection of irreversible switching in a single FePt nanosized dot

Magnetization of an isolated single dot as small as 60 nm in diameter fabricated from a single crystal L10-FePt(001) film has been measured by detection of the anomalous Hall effect in the temperature range from 10 to 300 K. Over the whole temperature range, the dots with diameter ranging from 60 nm to 12 μm exhibit perfect rectangular magnetization loops with coercivity almost constant regardless of the very large difference in diameter. The activation energy has been evaluated to be about 4×10−19 J, equivalent to the domain-wall energy times the square of the domain-wall thickness, suggesting that the magnetization reversals are initiated by nucleation of reversed embryo with the dimension of the exchange length.

Novel magnetostrictive memory device

A stress-operated memory device consisting of an ellipsoidal magnetic particle array and an electrostrictive grid is proposed. In the device, the magnetic state of the particle can be controlled only by the magnetostriction effect. Each particle is located at the intersection of the grid and has an in-plane uniaxial anisotropy. A pair of electric contacts is connected to the end of each wire. In the writing process, the driving voltages are simultaneously applied to two pairs of the selected contacts. This allows to apply a local electric field whose direction and amplitude can be regulated by varying the voltage intensity and polarity. The exerting stress on the magnetic particle results in the linear magnetostriction and hence an additional anisotropy energy in the particle. The in-plane total energy minimum, corresponding to the magnetization direction, follows the local electric field. Consequently the magnetization of the single magnetic particle located at the intersection can therefore be selective...

Cognitive function and frontal lobe atrophy in normal elderly adults: Implications for dementia not as aging‐related disorders and the reserve hypothesis

Abstract We examined the relations between cognitive function and age and education in the normal elderly population. As per the community‐based stroke, dementia, and bed confinement pre‐vention in the town of Tajiri, neuropsychological assessments, including the Cognitive Ability Screening Instrument (CASI), were performed for 99 randomly selected normal elderly subjects. We assessed the frontal function (working memory, word fluency, Trail‐Making Tests, CASI subitems of list‐generating fluency, attention, and concentration/mental manipulation), language function (proverbs, CASI subitem language), non‐language function (the digit symbol test of the Wechsler Adult Intelligence Scale‐Revised (WAIS‐R), CASI subitem visual construction), memory (Alzheimers Disease Assessment Scale recall/recognition, story recall, CASI subitems short and long‐term memory, the Rey‐Osterrieth Complex Figure Test), and the global function (CASI subitems orientation and abstraction and judgment). We found that the only test affected by age was the digit symbol test of the WAIS‐R. The effects of education were distributed among various tests. There was a significant correlation between age and the frontal lobe atrophy in the lower educated group. The present findings suggest that cognitive function is spared by the aging process itself and dementia should be considered as age‐related, not aging‐related disorders, and that education might have a protective effect on cognitive change, supporting the reserve hypothesis.

Study on the in-plane uniaxial anisotropy of high permeability granular films

We have investigated the uniaxial magnetic anisotropy of the high resistivity Fe–Al–O granular films prepared by sputtering. It is found that application of external dc field during film deposition and post-annealing treatments give rise to no serious effects on the magnetic anisotropy. In contrast, the incident angle of sputtered particles to the substrate greatly affects the strength and the direction of the anisotropy. These results suggest that the magnetic anisotropy is induced by a shape anisotropy due to anisotropic morphology in the films. The temperature dependence of the anisotropy constant, however, does not obey the usual shape anisotropy relationship Ku(T)∝Ms(T)2. In the present article, we propose an anisotropic coupling model in order to explain the uniaxial anisotropy found in these granular films, where the magnetic coupling between Fe grains is assumed to be anisotropic in the film plane due to the presence of low Tc intergranular phase which bridges the gap between Fe grains in one dire...

Vertical bistable switching of spin vortex in a circular magnetic dot

We have investigated switching behaviors of a spin-vortex core in circular magnetic dots to evaluate them as a new candidate for magnetic memory elements. The spin-vortex core with the lateral dimension of exchange length can take two possible states with spins around the dot center directing either up- or downward. These two spin configurations are very stable and their polarities can be switched by a large vertical field. The mean switching field reaches about 2.5 kOe for Ni80Fe20 dots with 1 μm in diameter and 80 nm in height. This result could open the way for developing a new bistable magnetic memory element utilizing the spin vortex.

Improved RF integrated magnetic thin-film inductors by means of micro slits and serface planalization techniques

Improvement of magnetic thin-film inductors for RF monolithic microwave integrated circuits (MMICs) is discussed. Surface planarization reduced the surface roughness down to R/sub a/=1.2 nm, which enhanced the quality factor by 14% over a nonplanarized inductor. The orthogonal bar slit pattern was the best among the fabricated slit patterns, L=7.55 nH (+12% of the air core), R=6.80 /spl Omega/ and Q=7.09 (+9%) were obtained for the orthogonal bar slit pattern (slit width=0.75 /spl mu/m) with surface planarization.

Application of bi-directional thin-film micro wire array to RF integrated spiral inductors

Vertically and horizontally aligned micro wire arrays with the magnetic hard axis perpendicular to the length of the wire are micro-fabricated from zero-magnetostrictive CoNbZr film. Annealing produced a 180-degree domain pattern, small coercive force and good permeability. Using the micro wire array with line/space=9 /spl mu/m/2 /spl mu/m, an RF integrated inductor exhibited L=7.5 nH(+11% of air cores), R=7.6 /spl Omega/ and Q=6.3 (almost same as the air cores).

Thermodynamic calculations of phase equilibria of Co–Cr–Pt ternary system and magnetically induced phase separation in the FCC and HCP phases

Abstract The calculations of phase equilibria of the Co–Cr–Pt ternary system have been carried out based on the thermodynamic assessments of Co–Cr, Co–Pt and Cr–Pt binary systems by the calculation of phase diagram technique. The Gibbs energies of the liquid, FCC, BCC and HCP solution phases were approximated by a sub-regular solution model, while those of σ and Cr3Pt phases were approximated by a compound energy model. Almost all the experimental information on each sub-system has been well described by the present set of thermodynamic parameters. A critical calculation of the magnetically induced miscibility gap between the ferromagnetic HCP and the paramagnetic HCP phase has been conducted, where the two-phase separation has been found at the Curie temperature. The Cr content in the ferromagnetic HCP phase increases and the width of the two-phase separation becomes narrower with increasing Pt content. The present calculations would be useful for the design and development of the perpendicular magnetic recording media.