arXiv subjects

Yoshishige Suzuki

Publications and source records attributed to Yoshishige Suzuki.

33 records · Page 2Linked to original sources

arXiv2015

Room-temperature operation of Si spin MOSFET with high on/off spin signal ratio

We experimentally demonstrate a Si spin metal-oxide-semiconductor field-effect transistor (MOSFET) that exhibits a high on/off ratio of source-drain current and spin signals at room temperature. The spin channel is non-degenerate n-type Si, and an effective application of gate voltage in the back-gated structure allows the spin MOSFET operation. This achievement can pave the way to practical use of the Si spin MOSFET.

cond-mat.mes-hall↗

arXiv2015

Study of spin dynamics and damping on the magnetic nanowire arrays with various nanowire widths

We investigate the spin dynamics including Gilbert damping in the ferromagnetic nanowire arrays. We have measured the ferromagnetic resonance of ferromagnetic nanowire arrays using vector-network analyzer ferromagnetic resonance (VNA-FMR) and analyzed the results with the micromagnetic simulations. We find excellent agreement between the experimental VNA-FMR spectra and micromagnetic simulations result for various applied magnetic fields. We find that the demagnetization factor for longitudinal conditions, Nz (Ny) increases (decreases) as decreasing the nanowire width in the micromagnetic simulations. For the transverse magnetic field, Nz (Ny) increases (decreases) as increasing the nanowire width. We also find that the Gilbert damping constant increases from 0.018 to 0.051 as the increasing nanowire width for the transverse case, while it is almost constant as 0.021 for the longitudinal case.

cond-mat.mtrl-sci↗

arXiv2014

Local magnetoresistance in Fe/MgO/Si lateral spin valve at room temperature

Room temperature local magnetoresistance in two-terminal scheme is reported. By employing 1.6 nm-thick MgO tunnel barrier, spin injection efficiency is increased, resulting in large non-local magnetoresistance. The magnitude of the non-local magnetoresistance is estimated to be 0.0057 ohm at room temperature. As a result, a clear rectangle signal is observed in local magnetoresistance measurement even at room temperature. We also investigate the origin of local magnetoresistance by measuring the spin accumulation voltage of each contact separately.

cond-mat.mtrl-sci↗

arXiv2012

An investigation of the inverted Hanle effect in highly-doped Si

The underlying physics of the inverted Hanle effect appearing in Si was experimentally investigated using a Si spin valve, where spin transport was realized up to room temperature. No inverted-Hanle-related signal was observed in a non-local 4-terminal scheme even the same ferromagnetic electrode was used, whereas the signal was detected in a non-local 3-terminal scheme. Although the origin of the inverted Hanle effect has been thought to be ascribed to interfacial roughness beneath a ferromagnetic electrode, our finding is inconsistent with the conventional interpretation. More importantly, we report that there were two different Hanle signals in a non-local 3-terminal scheme, one of which corresponds to the inverted Hanle signal but the other is ascribed to spin transport. These results strongly suggest that (1) there is room for discussion concerning the origin of the inverted Hanle effect, and (2) achievement of spin transport in a non-local 4-terminal scheme is indispensable for further understanding of spin injection, spin transport and spin coherence in Si. Our new findings provide a new and strong platform for arising discussion of the physical essence of Hanle-related spin phenomena.

cond-mat.mtrl-sci↗

arXiv2012

Observation of Huge Magnetoresistance and Multiferroic-like Behavior of Co Nanoparticles in a C60 matrix

Tunneling magnetoresistance (TMR) via oxides or molecules includes fruitful physics, such as spin filtering and hybridized interface states, in addition to various practical applications using large TMR ratio at room temperature. Then, a larger TMR effect with a new fundamental physics is awaited because further progress on spintronics can be realized. Here we report a discovery of a gigantic TMR ratio of 1,400,000% in a C60-Co nanocomposite spin device. The observed effect is induced by a combination of a Coulomb blockade effect and a novel magnetic switching effect. Theoretical investigation reveals that an electric field and a magnetic field control the magnetization and the electronic charging state, respectively, of the Co nanoparticles as in physics of multiferroicity.

cond-mat.mtrl-sci↗

arXiv2011

The effect of spin drift on spin accumulation voltages in highly-doped Si

An investigation was carried out into the effect of spin drift on spin accumulation signals in highly-doped Si using non-local 4-terminal (NL-4T) and 3-terminal (NL-3T) methods. The spin signals in the NL-4T scheme were not affected by spin drift, and the bias dependence was governed by whether spins were injected into or extracted from the Si channel. In contrast, the spin signal was strongly modulated by the bias electric field in the NL-3T scheme. The bias electric field dependence of the spin signals in the NL-3T method was quantitatively clarified using the spin drift-diffusion equation, and the results can be reasonably explained.

cond-mat.mtrl-sci↗

arXiv2011

Experimental Investigation of Spin Transport Properties in Silicon by Using a Non-local Geometry

A systematic investigation of spin transport properties in silicon at 8 K by using a non-local geometry is presented. The spin injection signal in the non-local scheme is found to increase in proportion to the evolution of bias electric currents. Theoretical fittings using the Hanle-type spin precession signals reveal that the spin polarization of the transported spin in the Si is much less affected by the change in the bias electric current compared with a case of the other spin devices, which induces a unique bias dependence of the spin signals.

cond-mat.mtrl-sci↗

arXiv2009

Analysis of Degradation in Graphene-based Spin Valves

The degradation mechanisms of multilayer graphene spin valves are investigated. The spin injection signals in graphene spin valves have been reported to be linearly dependent on the drain bias voltage, which indicates that the spin polarization of injected spins in graphene is robust against the bias voltage. We present that the disappearance of this robustness is due to two different degradation mechanisms of the spin valves. Our findings indicate that the disappearance of the robustness is due to degradation rather than an intrinsic characteristic of graphene. Thus, the robustness can be greatly enhanced if degradation can be prevented.

cond-mat.mes-hall↗

arXiv2009

Robustness of Spin Polarization in Graphene-based Spin Valves

Decrease of spin polarization in spintronics devices under an application of bias voltage is one of currently important problems which should be solved. We reveal unprecedented robustness of spin polarization in multi-layer graphene spin valves at room temperature. Surprisingly, the spin polarization of injected spins is constant up to a bias voltage of +2.7 V and -0.6 V in positive and negative bias voltage applications, which is dramatically superior to all spintronics devices. Our finding is induced by suppression of spin scattering due to an ideal interface formation. Furthermore, we firstly report on important accordance between theory and experiment in molecular spintronics by observing the fact that signal intensity in a local scheme is double of that in a non-local scheme as theory predicts, which provides construction of a steadfast physical basis in this field.

cond-mat.mtrl-sci↗

arXiv2009

Electrical Spin Injection into Silicon using MgO Tunnel Barrier

We observed spin injection into silicon through Fe/MgO tunnel barrier by using non-local magnetoresistance measurement technique. Fe/MgO tunnel barrier contacts with a lateral spin valve structure were fabricated on phosphorous doped silicon-on-insulator substrate. Spin injection signals in the non-local scheme were observed up to 120K, which is the highest value where band transferred spins in Si have ever been reported, and spin diffusion length was estimated to be about 2.25um at 8K. Temperature dependence and injection current dependence of the non-local voltage were also investigated. It is clarified that MgO tunnel barrier is effective for the spin injection into silicon.

cond-mat.mtrl-sci↗

arXiv2009

Voltage-assisted Magnetization Switching in Ultrathin Fe80Co20 Alloy Layers

Growing demands for the voltage-driven spintronic applications with ultralow-power consumption have led to new interest in exploring the voltage-induced magnetization switching in ferromagnetic metals. In this study, we observed a large perpendicular magnetic anisotropy change in Au(001) / ultrathin Fe80Co20(001) / MgO(001) / Polyimide / ITO junctions, and succeeded in realizing a clear switching of magnetic easy axis between in-plane and perpendicular directions. Furthermore, employing a perpendicularly magnetized film, voltage-induced magnetization switching in the perpendicular direction under the assistance of magnetic fields was demonstrated. These pioneering results may open a new window of electric-field controlled spintronics devices.

cond-mat.mtrl-sci↗

arXiv2008

Transfer Characteristics in Graphene Field-Effect Transistors with Co Contacts

Graphene field-effect transistors with Co contacts as source and drain electrodes show anomalous distorted transfer characteristics. The anomaly appears only in short-channel devices (shorter than approximately 3 micrometers) and originates from a contact-induced effect. Band alteration of a graphene channel by the contacts is discussed as a possible mechanism for the anomalous characteristics observed.

cond-mat.mtrl-sci↗

arXiv2008

Bias-driven large power microwave emission from MgO-based tunnel magnetoresistance devices

Spin-momentum transfer between a spin-polarized current and a ferromagnetic layer can induce steady-state magnetization precession, and has recently been proposed as a working principle for ubiquitous radio-frequency devices for radar and telecommunication applications. However, to-date, the development of industrially attractive prototypes has been hampered by the inability to identify systems which can provide enough power. Here, we demonstrate that microwave signals with device-compatible output power levels can be generated from a single magnetic tunnel junction with a lateral size of 100 nm, seven orders of magnitude smaller than conventional radio-frequency oscillators. We find that in MgO magnetic tunnel junctions the perpendicular torque induced by the spin-polarized current on the local magnetization can reach 25% of the in-plane spin-torque term, while exhibiting a different bias-dependence. Both findings contrast with the results obtained on all-metallic structures - previously investigated -, reflecting the fundamentally different transport mechanisms in the two types of structures.

cond-mat.other↗

arXiv2008

A Nuclear Magnetic Resonance Study on Rubrene-cobalt Nano-composites

We implemented a nuclear magnetic resonance (NMR) study on rubrene(C42H28)-Co nano-composites that exhibit an enhanced magnetoresistance (MR) ratio of 80%. The 59Co NMR spin echo experiment enabled clarification of the hyperfine field of Co at the interface between the ferromagnet and the molecules, which has not been investigated for molecular spintronics. An enhanced hyperfine field of the Co was observed in the rubrene-Co nano-composites, which may be related to the enhancement of the MR ratio. This study demonstrates the importance of microscopic investigation of the interface between molecules and ferromagnets that governs spin-dependent transport in molecular spin devices.

cond-mat.mtrl-sci↗

arXiv2007

Spin Injection into a Graphene Thin Film at Room Temperature

We demonstrate spin injection into a graphene thin film with high reliability by using non-local magnetoresistance (MR) measurements, in which the electric current path is completely separated from the spin current path. Using these non-local measurements, an obvious MR effect was observed at room temperature; and the MR effect was ascribed to magnetization reversal of ferromagnetic electrodes. This result is a direct demonstration of spin injection into a graphene thin film. Furthermore, this is the first report of spin injection into molecules at room temperature.

cond-mat.mtrl-sci↗