Hiroyasu Kawano

Origin of Negative Differential Resistance Observed on Bipolar Resistance Switching Device with Ti/Pr0.7Ca0.3MnO3/Pt Structure

Bipolar resistance switching was investigated on sputtered Pr0.7Ca0.3MnO3 (PCMO) sandwiched by Pt- and Ti-electrodes. Based on electrical conductivity measurements and a combination of electron energy loss spectroscopy analysis and transmission electron microscopy observation, we found that the negative differential resistance observed in the forming process originates from the motion of oxygen ions at the Ti/PCMO interface. We propose that the observed resistance switching is caused by an oxidation/reduction reaction at the interface.

Enhancement of Switching Capability on Bipolar Resistance Switching Device with Ta/Pr0.7Ca0.3MnO3/Pt Structure

We found that Pr0.7Ca0.3MnO3 (PCMO) film sandwiched by a Ta top electrode (TE) and a Pt bottom electrode (BE) exhibited bipolar resistance switching similar to that of Ti(TE)/PCMO/Pt(BE). The switching capability of Ta/PCMO/Pt was greatly improved by pulse-forming compared to dc-forming, which are both pre-treatments to enable resistance switching by pulsed voltage. Switching speeds faster than 100 ns and rewrite cycles of more than 10,000 were obtained while maintaining a ratio of resistance change larger than 1,000%. The mechanism of resistance switching was explained by an oxidation/reduction reaction at the Ta/PCMO interface, as previously proposed for Ti/PCMO/Pt.

A numerical study of power loss factors in resonant magnetic coupling

We numerically studied the affect of power loss factors in a wireless power transfer system using resonant magnetic coupling. Resonant magnetic coupling is regarded as one of the most promising methods for mid-range wireless charging systems. To make this method practical, it is important to accurately estimate power transfer efficiency and effect of each loss factor in the device-designing stage. We conducted a numerical simulation using an equivalent circuit model and electromagnetic analysis for a mobile-device model. Resonance at 7 MHz between the transmitting and receiving coils was achieved using lumped capacitors attached at the coil ends. In addition to the skin effect, we consider various loss factors such as proximity effect, loss tangent of lumped capacitors, and so on. The results show that the proximity effect significantly decreases the power transfer efficiency of the system, and the loss tangent of lamped capacitor also decreases it by a few percentage points.

Phase and intensity control of multiple coil currents in resonant magnetic coupling

We studied the effects of the phase and intensity of multiple coil currents in a wireless power transfer system using resonant magnetic coupling. Resonant magnetic coupling is regarded as one of the most promising methods for mid-range wireless charging systems. For mid-range charging, the charging device can assume various positions and postures, and some of the conditions make wireless charging difficult. To solve this problem, we propose a method to control the phase and intensity of multiple coil currents. By performing numerical simulations using an equivalent circuit model and electromagnetic analysis, we confirmed that it had the desired effect.

Improvement of Recording Density of Amorphous TbFeCo Magnetic Recording Layer on FeC Soft Magnetic Back Layer

The effect of the surface morphology of an intermediate layer on recording density was studied for perpendicular magnetic recording media composed of an FeC soft magnetic back layer, a nonmagnetic intermediate layer and an amorphous TbFeCo perpendicular magnetic recording layer. We confirmed that the formation of a very thin intermediate layer with small grains enabled high-density recording on the TbFeCo recording layer. The intermediate layer was 3 nm thick and the grain diameter was about 13 nm. The intermediate layer had a multilayered structure, which consisted of a dielectric layer, two metallic layers, and a C layer. The D50 of the media with the multilayered intermediate layer was 100 kilo flux changes per inch (kFCI) higher than that of the media with a single-layer intermediate layer. In addition, the roll-off characteristic was considerably improved by differentiating the row read head response; D50 was 395 kFCI.

Effect of underlayer on soft magnetic properties of electroless plated CoFeNi films

The soft magnetic properties of electroless plated CoFeNi films were examined in terms of the underlayers. CoFeNi films on NiP underlayers had a high saturation flux density of 1.7 T and a small coercivity of less than approximately 300 A/m when the film thickness was more than 300 nm. With a thickness of less than 300 nm, however, the saturation flux density was significantly reduced, while the coercivity drastically increased. These properties could be improved by utilizing a NiFe underlayer, instead of a NiP underlayer, to improve the film structure around the interface between the CoFeNi film and the underlayer.

Air gap dependence of write and read characteristics in magneto-optical recording with solid immersion lens

A near-field MO recording was done at a wavelength of 680 nm using a super-hemispherical solid immersion lens (SIL) flying head. The SIL optical system has a designed NA of 1.46. The SIL can write and read marks to a minimum length of about 0.15 /spl mu/m. The optical readout characteristic with the SIL is not very sensitive to air gaps if the air gaps are kept below about 130 nm.

Suppression of Spike Noise from FeCSi Film for Backlayer of Double-Layered Perpendicular Magnetic Recording Medium

The relationships among magnetic properties, noise characteristics, and structures of FeCSi laminated films developed as soft magnetic backlayers of double-layered perpendicular magnetic recording media were examined to find a way to suppress spike noise. FeCSi laminated films were fabricated by alternately stacking soft magnetic layers with non-magnetic intermediate layers. The periods of the cross-tie walls in FeCSi monolayers lengthened as the film thickness decreased. The periods of the cross-tie walls in the laminated films were longer than those in the monolayers. This indicated that the lamination technique was effective in preventing free poles from forming on the surface of the laminated films and that amplitudes of spike noise from the laminated films should have been suppressed. By using FeCSi soft magnetic layers with a thickness of 20 nm and carbon intermediate layers with a thickness of 5 nm, amplitudes of spike noise from the laminated films were suppressed sufficiently for practical use. The laminated films had a high saturation magnetization of 1.6 T and low media noise that was on the same level as in conventional longitudinal magnetic recording media.

Loss Simulation by Finite-Element Magnetic Field Analysis Considering Dielectric Effect and Magnetic Hysteresis in EI-Shaped Mn-Zn Ferrite Core

Power electronic devices such as inductors and transformers are required to be driven with high frequency according to downsizing. Mn-Zn ferrite is one of the high-frequency magnetic materials. The dimensional resonance occurs in Mn-Zn cores due to the increase of the dielectric constant and significantly affects the eddy current loss [1]. The equivalent RC circuit of Mn-Zn ferrite was modeled by the grains and their boundary layers and can explain the effective dielectric property by the contribution of the capacitance [2]. The boundary layers with high-resistance suppress the eddy current in the grains at low frequencies, while as frequency increases the suppression of the eddy current decreases by charge accumulation on the surface of the grains. The calculating method of the frequency dependent dielectric property by the capacitance was proposed and the dimensional resonance was reproduced by applying the method to the magnetic field equations of linear magnetic materials by using a cylindrical approximation [3]. In order to analyze the eddy current loss of complex shaped inductors at high frequencies, we apply the dielectric effect to the A-

Variable-resistance element

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