Takeshi Seki 교수

Current-induced magnetization reversal of perpendicularly magnetized layers was studied in current-perpendicular-to-plane giant magnetoresistance pillars with L10-FePt (001) layers. The FePt layers exhibited strong perpendicular magnetic anisotropy of the order of 107erg∕cm3. A series of magnetoresistance curves after applying pulse currents with different current densities showed that current-induced magnetization reversal from an antiparallel to a parallel alignment occurred at the current den

In this paper, a Dynamic Voltage and Frequency Management (DVFM) scheme introduced in a microprocessor for handheld devices with wideband embedded DRAM is reported. Our DVFM scheme reduces the power consumption effectively by cooperation of the autonomous clock frequency control and the adaptive supply voltage control. The clock frequency is controlled using hardware activity information to determine the minimum value required by the current processor load. This clock frequency control is realiz

We have investigated the effect of extensive compositional change on the structure and magnetic properties of FePt sputtered films deposited at a substrate temperature of 300 °C. The Fe concentration in the FePt films was varied from 19 to 68 at. %. In the x-ray diffraction patterns, (001) and (003) superlattice peaks were observed at a Pt-rich composition range, indicating the formation of a L10 ordered structure. A L10 ordered Fe38Pt62 film exhibited perpendicular magnetization with a large un

The coercivity (Hc) of a perpendicularly magnetized FePt layer was modulated by applying the voltage (Vapp) to a Hall device through MgO and Al–O insulating layers. A change in ∼40 Oe in Hc was observed by changing Vapp from −13 to 13 V. From the quantitative analysis of the voltage effect on Hc, the change in the anisotropy energy by voltage application was evaluated to be 18.6 fJ/V m, which was of the same order as the theoretical prediction. The role of the MgO layer for the voltage effect wa

Spatial distribution of temperature modulation due to the anomalous Ettingshausen effect (AEE) is visualized in a ferromagnetic FePt thin film with in-plane and out-of-plane magnetizations using the lock-in thermography technique. Comparing the AEE of FePt with the spin Peltier effect (SPE) of a Pt/yttrium iron garnet junction provides direct evidence of different symmetries of AEE and SPE. Our experiments and numerical calculations reveal that the distribution of heat sources induced by AEE str

The spin anomalous Hall effect (SAHE), generating spin angular momentum flow (spin current, ${\mathbf{J}}_{\mathrm{s}})$, in an $L{1}_{0}\text{\ensuremath{-}}\mathrm{FePt}$ ferromagnet was quantitatively evaluated by exploiting giant magnetoresistance devices composed of $L{1}_{0}\text{\ensuremath{-}}\mathrm{FePt}|\mathrm{Cu}|\mathrm{N}{\mathrm{i}}_{81}\mathrm{F}{\mathrm{e}}_{19}$. From the ferromagnetic resonance linewidth modulated by the charge current $({\mathbf{J}}_{\mathrm{c}})$ injection,

The effect of spin-transfer torque in 90° magnetization configuration on current-induced magnetization reversal was studied in current-perpendicular-to-plane giant magnetoresistance pillars of in-plane magnetized FePt∕Au∕FePt trilayers combined with an L10-FePt perpendicular spin polarizer. The resistance change associated with the transition of the alignment of the two in-plane magnetizations was observed, showing no significant difference in the magnitude from that of a pillar without the perp

We investigated anomalous Ettingshausen effect (AEE) and anomalous Nernst effect (ANE) for the same device consisting of an FePt thin film. The temperature modulation due to the AEE was visualized using the active infrared emission microscopy, called lock-in thermography. On the other hand, the ANE voltage was detected under the temperature gradient induced by the heater built into the device. We experimentally evaluated the magnitudes of AEE and ANE, taking into account the heat loss to the sub

We experimentally observed the inverse spin Hall effect (ISHE) of ferromagnetic FePt alloys. Spin Seebeck effect due to the temperature gradient generated the spin current (Js) in the FePt|Y3Fe5O12 (YIG) structure, and Js was injected from YIG to FePt and converted to the charge current through ISHE of FePt. The significant difference in magnetization switching fields for FePt and YIG led to the clear separation of the voltage of ISHE from that of anomalous Nernst effect in FePt. We also investi

We report an enhancement of the anomalous Nernst effect (ANE) in Ni/Pt (001) epitaxial superlattices. The transport and magnetothermoelectric properties were investigated for the Ni/Pt superlattices with various Ni layer thicknesses ($t$). The anomalous Nernst coefficient was increased up to more than $1\phantom{\rule{0.16em}{0ex}}\ensuremath{\mu}\mathrm{V}\phantom{\rule{0.16em}{0ex}}{\mathrm{K}}^{\ensuremath{-}1}$ for $2.0\phantom{\rule{0.16em}{0ex}}\mathrm{nm}\ensuremath{\le}t\ensuremath{\le}4

The magnetic properties of Fe38Pt62 and Fe52Pt48 films sputter deposited on MgO (001) substrates with and without a buffer layer at the substrate temperature Ts of 300 °C have been investigated. Pt, Au, and PtAu alloys with different compositions were used as the buffer layer to study the influence of the lattice mismatch between the FePt layer and the buffer layer. The L10 ordered structure with large perpendicular magnetic anisotropy has been obtained for the Fe38Pt62 films irrespective of the

L 1 0 - Fe Pt (001) and L10-FePt (110) dot arrays with well-defined geometry were fabricated through the use of electron beam lithography and Ar ion etching. The lateral size of dots was varied in the range from 0.2×0.2to5×5μm2. Coercivity (Hc) for the perpendicularly magnetized FePt (001) dots increases with decreasing the dot size. In the case of the FePt (110) dots with in-plane magnetization, on the other hand, the dot size dependence of Hc is completely different from that for FePt (001) do