Spin Relaxation Characteristics Research Articles

Gate-Driven Pure Spin Current in Graphene

Spintronics, which utilizes spin as information carrier, is a promising solution for nonvolatile memory and low-power computing in the post-Moore era. An important challenge is to realize long distance spin transport, together with efficient manipulation of spin current for novel logic-processing applications. Here, we describe a gate-variable spin current demultiplexer (GSDM) based on graphene, serving as a fundamental building block of reconfigurable spin current logic circuits. The concept relies on electrical gating of carrier density dependent conductivity and spin diffusion length in graphene. As a demo, GSDM is realized for both single-layer and bilayer graphene. The distribution and propagation of spin current in the two branches of GSDM depend on spin relaxation characteristics of graphene. Compared with Elliot-Yafet spin relaxation mechanism, D'yakonov-Perel mechanism results in more appreciable gate-tuning performance. These unique features of GSDM would give rise to abundant spin logic applications, such as on-chip spin current modulators and reconfigurable spin logic circuits.

The Impurity Spin-Dependent Scattering Effects in the Transport and Spin Resonance of Conduction Electrons in Bismuth Doped Silicon

Transport and spin relaxation characteristics of the conduction electrons in silicon samples doped with bismuth in the 1.1·1013 - 7.7·1015 cm-3 concentration range were studied by the Hall and electron spin resonance spectroscopy. Hall effect measurements in the temperature range 10-80 K showed a deviation from the linear dependence of the Hall resistance in the magnetic field, which is a manifestation of the anomalous Hall effect. The magnetoresistance investigation shows that with current increasing magnetoresistance may change its sign from positive to negative, which is most clearly seen when the bismuth concentration goes up to 7.7·1015 cm-3. The conduction electron spin relaxation rate dramatically increases in silicon samples with sufficiently low concentration of bismuth ~ 2·1014 cm-3. All these results can be explained in terms of the concept of spin-dependent and spin flip scattering induced by heavy bismuth impurity centers.

Spin relaxation characteristics in Ag nanowire covered with various oxides

We have studied spin relaxation characteristics in a Ag nanowire covered with various oxide layers of Bi2O3, Al2O3, HfO2, MgO, or AgOx by using non-local spin valve structures. The spin-flip probability, a ratio of momentum relaxation time to spin relaxation time at 10 K, exhibits a gradual increase with an atomic number of the oxide constituent elements, Mg, Al, Ag, and Hf. Surprisingly, the Bi2O3 capping was found to increase the probability by an order of magnitude compared with other oxide layers. This finding suggests the presence of an additional spin relaxation mechanism such as Rashba effect at the Ag/Bi2O3 interface, which cannot be explained by the simple Elliott-Yafet mechanism via phonon, impurity, and surface scatterings. The Ag/Bi2O3 interface may provide functionality as a spin to charge interconversion layer.

Spin dynamics and spin noise in the presence of randomly varying spin–orbit interaction in a semiconductor quantum wire

Using ensemble Monte Carlo simulation, we have studied hot carrier spin dynamics and spin noise in a multi-subband GaAs quantum wire in the presence of a randomly varying Rashba spin–orbit interaction. The random variation reduces the carrier ensemble’s spin dephasing time due to the D’yakonov–Perel’ mechanism, but otherwise makes no qualitative difference to the temporal spin relaxation characteristics. However, it makes a qualitative difference to the spatial spin relaxation characteristics which change from monotonic and smooth to non-monotonic and chaotic because of a complex interplay between carriers in different subbands. As far as spin fluctuation and spin noise are concerned, the random variation has no major effect except that the low-frequency noise power spectral density increases slightly when the magnitude of the Rashba spin–orbit interaction field is varied randomly while holding the direction constant.

Identification of Substitutional Nitrogen and Surface Paramagnetic Centers in Nanodiamond of Dynamic Synthesis by Electron Paramagnetic Resonance

Production of nanodiamond particles containing substitutional nitrogen is important for a wide variety of advanced applications. In the current work nanodiamond particles synthesized from a mixture of graphite and hexogen were analyzed to determine the presence of substitutional nitrogen using pulsed electron paramagnetic resonance (EPR) spectroscopy. Nitrogen paramagnetic centers in the amount of 1.2 ppm have been identified. The spin relaxation characteristics for both nitrogen and surface defects are also reported. A new approach for efficient depletion of the strong nonnitrogen EPR signal in nanodiamond material by immersing nanodiamond particles into ice matrix is suggested. This approach allows an essential decrease of the spin relaxation time of the dominant non-nitrogen defects, while preserving the substitutional nitrogen spin relaxation time.

Nuclear magnetic resonance relaxation studies of plant polyester dynamics. 2. Suberized potato cell wall

Measurements of the proton rotating-frame relaxation time T 1ρ (H) indicate that wound-healing involves the formation of spatially separated suberin and cell-wall domains. Suberin appears to be attached to the cell-wall domain at discrete sites, with both its methylene and phenylpropanoid groups divided into two populations having distinct chemical shifts and spin relaxation characteristics. Measurements of T 1ρ (C) and T 1 (C) in this biopolymer system sho significant site-specific and tissue-specific variations .

Ubisemiquinone in the NADH-ubiquinone reductase region of the mitochondrial respiratory chain

Coupled bovine heart submitochondrial particles exhibit a rotenone-sensitive g = 2.00 low-temperature EPR signal attributable to ubisemiquinone which is observed during steady-state electron transfer from NADH to oxygen or from succinate to NAD + in Δ \\ ̃ gmH +-dependent reverse electron transfer. Quantitation of the signal under optimal conditions gives a value for maximal semiquinone of approx. 0.5 spins per spin of the fully reduced NADH dehydrogenase iron-sulfur center N-2. The intensity of the signal is drastically reduced when electron transfer from NADH to oxygen is blocked by cyanide or in the case of the reverse electron transfer from succinate to NAD + being prevented by anaerobiosis. Only those particles which contain ‘turnover-preconditioned” NADH-ubiquinone reductase demonstrate the ubisemiquinone signal together with N-1, N-2, N-3 and N-4 iron-sulfur centers. The spin relaxation characteristics of the rotenone-sensitive ubisemiquinone signal point to its interaction with one of the rapidly relaxing (4Fe-4S) centers, most probably N-2.

Electrical and paramagnetic properties of thermodonors-II in silicon. Discussion of a model

The formation and properties of thermodonors-II (TD-II, Tanneal = 650 °C) in Czochralski-grown silicon crystals are studied experimentally (EPR, Hall effect) and theoretically. Additionally the energy level spectrum and the paramagnetic properties of TD-II are investigated. A model of TD-II is proposed, which takes into consideration the localization of electrons on crystalline potential fluctuations due to oxygen clusters. The model explains the presence of the quasicontinuous spectrum of TD-II levels as well as the dependence of the depth of their location on the size of oxygen clusters. The g-factor shift, asymmetry, anisotropy of the electron paramagnetic resonance (EPR) line width and spin relaxation characteristics of TD-II, as well as the dependence of the parameters of centers on the duration of annealing, and the presence of acceptors introduced either through doping or γ-irradiation of the specimens are also explained. [Russian Text Ignored].

ChemInform Abstract: CONDUCTION‐ AND LOCALIZED‐ELECTRON SPIN RESONANCE IN THE LITHIUM‐METHYLAMINE SYSTEM: INFERENCES FOR THE EXISTENCE OF THE METALLIC COMPOUND TETRAMETHYLAMINELITHIUM(ZERO), LI(CH3NH2)4

Electron spin resonance (ESR) studies of fluid and frozen solutions of lithium in anhydrous methylamine are reported. The composition and temperature dependence of the ESR properties (electron spin relaxation times, electronic ge factor) are indicative of metallic compound formation in the lithium–methylamine system at low temperatures. Marked changes in both the electron spin relaxation properties and the ESR line shapes in the temperature interval 156–158 K are consistent with those expected for a metallic system moving through the melting point. Electron spin relaxation characteristics of the corresponding metal–ammonia compounds Li(NH3)4 and Ca(NH3)6 have been adequately interpreted in terms of a nearly free‐electron (NFE) picture for these low electron density materials. In contrast, electronic properties of the compound tetramethylaminelithium(zero), although nominally metallic (σ∼400 Ω−1 cm−1 for a 22 mole% metal fluid solution), cannot be described in the context of a NFE material. In particular, ...

Conduction- and localized-electron spin resonance in the lithium–methylamine system: Inferences for the existence of the metallic compound tetramethylaminelithium(zero), Li(CH3NH2)4

Electron spin resonance (ESR) studies of fluid and frozen solutions of lithium in anhydrous methylamine are reported. The composition and temperature dependence of the ESR properties (electron spin relaxation times, electronic ge factor) are indicative of metallic compound formation in the lithium–methylamine system at low temperatures. Marked changes in both the electron spin relaxation properties and the ESR line shapes in the temperature interval 156–158 K are consistent with those expected for a metallic system moving through the melting point. Electron spin relaxation characteristics of the corresponding metal–ammonia compounds Li(NH3)4 and Ca(NH3)6 have been adequately interpreted in terms of a nearly free-electron (NFE) picture for these low electron density materials. In contrast, electronic properties of the compound tetramethylaminelithium(zero), although nominally metallic (σ∼400 Ω−1 cm−1 for a 22 mole% metal fluid solution), cannot be described in the context of a NFE material. In particular, conduction electron spin relaxation properties reveal a breakdown in the Elliott treatment of spin relaxation in pure metals. We take this as evidence for incipient localization in the very strong scattering electronic regime. It is shown that an enhancement of the electron spin relaxation time relative to the predicted Elliott value in Li(CH3NH2)4 arises quite naturally if one considers the increasing importance of electron–electron and electron–phonon interaction in the approach to the metal nonmetal transition. This changeover in electron spin relaxation characteristics in lithium–methylamine solutions is correlated with the corresponding changes in the electronic conductivity. We suggest that the enhancement in the electron spin relaxation time can be used as an indicator, albeit qualitative, of the degree of localization of the electronic wave function in a nominally metallic system. This behavior contrasts markedly with that of nuclear spin relaxation in the lithium–methylamine system, where incipient localization gives rise to an enhancement in the nuclear relaxation rate relative to that predicted for a metallic system.