Biomedical subjects

D Chiba

Publications and source records attributed to D Chiba.

9 recordsLinked to original sources

PubMed2006

Velocity of domain-wall motion induced by electrical current in the ferromagnetic semiconductor (Ga,Mn)As.

Current-induced domain-wall motion with velocity spanning over 5 orders of magnitude up to 22 m/s has been observed by the magneto-optical Kerr effect in (Ga,Mn)As with perpendicular magnetic anisotropy. The data are employed to verify theories of spin transfer by the Slonczewski-like mechanism as well as by the torque resulting from spin-flip transitions in the domain-wall region. Evidence for domain-wall creep at low currents is found.

Journal Article↗

PubMed2006

Domain-wall resistance in ferromagnetic (Ga,Mn)As.

A series of microstructures designed to pin domain walls (DWs) in (Ga,Mn)As with perpendicular magnetic anisotropy has been employed to determine extrinsic and intrinsic contributions to DW resistance. The former is explained quantitatively as resulting from a polarity change in the Hall electric field at DW. The latter is 1 order of magnitude greater than a term brought about by anisotropic magnetoresistance and is shown to be consistent with disorder-induced mistracking of the carrier spins subject to spatially varying magnetization.

Journal Article↗

PubMed2004

Current-driven magnetization reversal in a ferromagnetic semiconductor (Ga,Mn)As/GaAs/(Ga,Mn)As tunnel junction.

Current-driven magnetization reversal in a ferromagnetic semiconductor based (Ga,Mn)As/GaAs/(Ga,Mn)As magnetic tunnel junction is demonstrated at 30 K. Magnetoresistance measurements combined with current pulse application on a rectangular 1.5 x 0.3 microm2 device revealed that magnetization switching occurs at low critical current densities of 1.1-2.2 x 10(5) A/cm2 despite the presence of spin-orbit interaction in the p-type semiconductor system. Possible mechanisms responsible for the effect are discussed.

Journal Article↗

PubMed2004

Current-induced domain-wall switching in a ferromagnetic semiconductor structure.

Magnetic information storage relies on external magnetic fields to encode logical bits through magnetization reversal. But because the magnetic fields needed to operate ultradense storage devices are too high to generate, magnetization reversal by electrical currents is attracting much interest as a promising alternative encoding method. Indeed, spin-polarized currents can reverse the magnetization direction of nanometre-sized metallic structures through torque; however, the high current densities of 10(7)-10(8) A cm(-2) that are at present required exceed the threshold values tolerated by the metal interconnects of integrated circuits. Encoding magnetic information in metallic systems has also been achieved by manipulating the domain walls at the boundary between regions with different magnetization directions, but the approach again requires high current densities of about 10(7) A cm(-2). Here we demonstrate that, in a ferromagnetic semiconductor structure, magnetization reversal through domain-wall switching can be induced in the absence of a magnetic field using current pulses with densities below 10(5) A cm(-2). The slow switching speed and low ferromagnetic transition temperature of our current system are impractical. But provided these problems can be addressed, magnetic reversal through electric pulses with reduced current densities could provide a route to magnetic information storage applications.

Journal Article↗

PubMed2003

Electrical manipulation of magnetization reversal in a ferromagnetic semiconductor.

We report electrical manipulation of magnetization processes in a ferromagnetic semiconductor, in which low-density carriers are responsible for the ferromagnetic interaction. The coercive force HC at which magnetization reversal occurs can be manipulated by modifying the carrier density through application of electric fields in a gated structure. Electrically assisted magnetization reversal, as well as electrical demagnetization, has been demonstrated through the effect. This electrical manipulation offers a functionality not previously accessible in magnetic materials and may become useful for reversing magnetization of nanoscale bits for ultrahigh-density information storage.

Journal Article↗

PubMed2000

Morphogenetic behavior of periodontium on inorganic implant materials: an experimental study of canines.

Periodontal ligament derived cells have the potential to regenerate all the components of the periodontium on the surface of inorganic implants, as well as on dentin. This suggests the hypothesis that the nature of the material affects the migration, proliferation, and differentiation of the progenitor cells for periodontium formation. To clarify this hypothesis, we evaluated the material-specific morphogenetic potential of periodontium-derived cells using an animal model for inducing cell migration from the functioning periodontium onto bioactive (hydroxyapatite, HA) and bioinert (titanium alloy, TA) material. Histologically, total periodontium including calcified cementum-like tissue only formed on HA and not on TA. Morphometrically, however, the length of fibrous connective tissue formed on HA was the same as on TA. This suggests that the bioactivity of the material does not affect the migration of periodontium-derived cells but strongly influences cell differentiation.

Animals↗

PubMed2000

Controlled local application of basic fibroblast growth factor (FGF-2) accelerates the healing of GBR. An experimental study in beagle dogs.

This animal study was performed to ascertain whether the regeneration of membrane-protected bone defects can be accelerated by the controlled application of basic fibroblast growth factor (FGF-2) using a new drug delivery system. Standardized alveolar bone defects were made surgically in 9 beagle dogs, and FGF-2 was administered using specially made collagen minipellets. A minipellet containing either 0.15 microgram FGF-2 (FGF) or 0 microgram FGF-2 (placebo) was placed in the defect or no minipellet was used (control), and bone regeneration was evaluated radiologically, histologically, and histometrically 8 weeks after the operation. Radiographs showed a surprisingly large radiopaque region in FGF sites compared with placebo or control sites. Histologically, mature bone filled the majority of the inner space of the membrane-protected defect in FGF sites. New bone formation was also seen in the control and the placebo sites, however, it filled less than half the area of the defect. Histometrically, the area of regenerated bone in FGF sites was significantly higher than in the other sites (P < 0.01). These results demonstrate that the controlled application of FGF-2 accelerates bone regeneration in membrane-protected bone defects in the canine model.

Alveolar Process↗

PubMed1998

Effect of polyelectrolyte complex (PEC) on human periodontal ligament fibroblast (HPLF) functions in the presence of glucocorticoids.

Cell functions in vivo are stimulated by extracellular matrices, vitamins, growth factors, and hormones. In this paper, the effects of glucocorticoids, dexamethasone (Dex), and Cortexrone (Cor) on the growth and differentiation of human periodontal ligament fibroblast (HPLF) were discussed in relation to a polyelectrolyte complex (PEC) consisting of polysaccharides (chitin, cellulose derivatives, and chitosan) as a tissue-culture material. A Dex-treatment at a concentration of 10(-)-10(-7) M inhibited one-half of HPLF growth in comparison with 10(-9) M Dex-treatment and no additive medium and produced aggregates on the chitosan-sulfated chitin PEC (SPECs) with regard to the degree of sulfate substitution. On the chitosan-sulfated cellulose PEC, 10(-7)-10(-9) M Dex-treatment promoted HPLF growth and inhibited the production of aggregates. On the other hand, a Cor-treatment, a mineral corticoid, which inhibits the interaction between Dex and its receptor, increased HPLF growth on SPEC141, but the HPLF did not construct aggregates. A Dex and Cor mixture-treatment inhibited one-third HPLF growth in comparison with 10(-5) M Dex-treatment and produced aggregates on PEC. The cooperative effect of both the culture material and hormones was found to control HPLF growth and morphology. The alkaline phosphatase (ALPase) activities of HPLF increased with an increase in the Dex and Cor concentration. The value of Dex-treated HPLF ALPase activity demonstrated a two-fold increase from that with Cor-treatment. The ALPase activity of Dex and Cor mixture-treated HPLF on PEC decreased with an increase in the Cor concentration, because Cor increased HPLF growth on PEC. In using carboxymethylated chitin derivatives as the polyanion, HPLF decreased in cell growth and produced aggregates in the absence of the additives, suggesting that PEC induces HPLF differentiation using only the stimulation of the material surface.

Alkaline Phosphatase↗

PubMedDate not supplied

Electric-field control of ferromagnetism.

It is often assumed that it is not possible to alter the properties of magnetic materials once they have been prepared and put into use. For example, although magnetic materials are used in information technology to store trillions of bits (in the form of magnetization directions established by applying external magnetic fields), the properties of the magnetic medium itself remain unchanged on magnetization reversal. The ability to externally control the properties of magnetic materials would be highly desirable from fundamental and technological viewpoints, particularly in view of recent developments in magnetoelectronics and spintronics. In semiconductors, the conductivity can be varied by applying an electric field, but the electrical manipulation of magnetism has proved elusive. Here we demonstrate electric-field control of ferromagnetism in a thin-film semiconducting alloy, using an insulating-gate field-effect transistor structure. By applying electric fields, we are able to vary isothermally and reversibly the transition temperature of hole-induced ferromagnetism.

Journal Article↗