237 research outputs found
Enhanced spin accumulation at room temperature in graphene spin valves with amorphous carbon interfacial layers
We demonstrate a large enhancement of the spin accumulation in monolayer
graphene following electron-beam induced deposition of an amorphous carbon
layer at the ferromagnet-graphene interface. The enhancement is 10^4-fold when
graphene is deposited onto poly(methyl metacrylate) (PMMA) and exposed with
sufficient electron-beam dose to cross-link the PMMA, and 10^3-fold when
graphene is deposited directly onto SiO2 and exposed with identical dose. We
attribute the difference to a more efficient carbon deposition in the former
case due to an increase in the presence of compounds containing carbon, which
are released by the PMMA. The amorphous carbon interface can sustain very large
current densities without degrading, which leads to very large spin
accumulations exceeding 500 microeVs at room temperature
Spin precession and spin Hall effect in monolayer graphene/Pt nanostructures
Spin Hall effects have surged as promising phenomena for spin logics
operations without ferromagnets. However, the magnitude of the detected
electric signals at room temperature in metallic systems has been so far
underwhelming. Here, we demonstrate a two-order of magnitude enhancement of the
signal in monolayer graphene/Pt devices when compared to their fully metallic
counterparts. The enhancement stems in part from efficient spin injection and
the large resistivity of graphene but we also observe 100% spin absorption in
Pt and find an unusually large effective spin Hall angle of up to 0.15. The
large spin-to-charge conversion allows us to characterise spin precession in
graphene under the presence of a magnetic field. Furthermore, by developing an
analytical model based on the 1D diffusive spin-transport, we demonstrate that
the effective spin-relaxation time in graphene can be accurately determined
using the (inverse) spin Hall effect as a means of detection. This is a
necessary step to gather full understanding of the consequences of spin
absorption in spin Hall devices, which is known to suppress effective spin
lifetimes in both metallic and graphene systems.Comment: 14 pages, 6 figures. Accepted in 2D Materials.
https://doi.org/10.1088/2053-1583/aa882
Spin accumulation probed in multiterminal lateral all-metallic devices
We study spin accumulation in an aluminium island, in which the injection of
a spin current and the detection of the spin accumulation are done by means of
four cobalt electrodes that connect to the island through transparent tunnel
barriers. Although the four electrodes are designed as two electrode pairs of
the same shape, they nonetheless all exhibit distinct switching fields. As a
result the device can have several different magnetic configurations. From the
measurements of the amplitude of the spin accumulation, we can identify these
configurations, and using the diffusion equation for the spin imbalance, we
extract the spin relaxation length ~nm and an
interface spin current polarization at low temperature and
~nm, at room temperature
Fingerprints of Inelastic Transport at the Surface of the Topological Insulator Bi2Se3: Role of Electron-Phonon Coupling
We report on electric-field and temperature dependent transport measurements
in exfoliated thin crystals of BiSe topological insulator. At low
temperatures ( K) and when the chemical potential lies inside the bulk
gap, the crystal resistivity is strongly temperature dependent, reflecting
inelastic scattering due to the thermal activation of optical phonons. A linear
increase of the current with voltage is obtained up to a threshold value at
which current saturation takes place. We show that the activated behavior, the
voltage threshold and the saturation current can all be quantitatively
explained by considering a single optical phonon mode with energy meV. This phonon mode strongly interacts with the surface states of
the material and represents the dominant source of scattering at the surface at
high electric fields.Comment: Supplementary Material at:
http://journals.aps.org/prl/supplemental/10.1103/PhysRevLett.112.086601/TIPhonon_SM.pd
Hot-Carrier Seebeck Effect: Diffusion and Remote Detection of Hot Carriers in Graphene
We investigate hot carrier propagation across graphene using an electrical
nonlocal injection/detection method. The device consists of a monolayer
graphene flake contacted by multiple metal leads. Using two remote leads for
electrical heating, we generate a carrier temperature gradient that results in
a measurable thermoelectric voltage VNL across the remaining (detector) leads.
Due to the nonlocal character of the measurement, VNL is exclusively due to the
Seebeck effect. Remarkably, a departure from the ordinary relationship between
Joule power P and VNL, VNL ~ P, becomes readily apparent at low temperatures,
representing a fingerprint of hot-carrier dominated thermoelectricity. By
studying VNL as a function of bias, we directly determine the carrier
temperature and the characteristic cooling length for hot-carrier propagation,
which are key parameters for a variety of new applications that rely on
hot-carrier transport
Spin communication over 30 m long channels of chemical vapor deposited graphene on SiO
We demonstrate a high-yield fabrication of non-local spin valve devices with
room-temperature spin lifetimes of up to 3 ns and spin relaxation lengths as
long as 9 m in platinum-based chemical vapor deposition (Pt-CVD)
synthesized single-layer graphene on SiO/Si substrates. The spin-lifetime
systematically presents a marked minimum at the charge neutrality point, as
typically observed in pristine exfoliated graphene. However, by studying the
carrier density dependence beyond n ~ 5 x 10 cm, via
electrostatic gating, it is found that the spin lifetime reaches a maximum and
then starts decreasing, a behavior that is reminiscent of that predicted when
the spin-relaxation is driven by spin-orbit interaction. The spin lifetimes and
relaxation lengths compare well with state-of-the-art results using exfoliated
graphene on SiO/Si, being a factor two-to-three larger than the best values
reported at room temperature using the same substrate. As a result, the spin
signal can be readily measured across 30 m long graphene channels. These
observations indicate that Pt-CVD graphene is a promising material for
large-scale spin-based logic-in-memory applications
Spin precession in anisotropic media
We generalize the diffusive model for spin injection and detection in
nonlocal spin structures to account for spin precession under an applied
magnetic field in an anisotropic medium, for which the spin lifetime is not
unique and depends on the spin orientation.We demonstrate that the spin
precession (Hanle) line shape is strongly dependent on the degree of anisotropy
and on the orientation of the magnetic field. In particular, we show that the
anisotropy of the spin lifetime can be extracted from the measured spin signal,
after dephasing in an oblique magnetic field, by using an analytical formula
with a single fitting parameter. Alternatively, after identifying the
fingerprints associated with the anisotropy, we propose a simple scaling of the
Hanle line shapes at specific magnetic field orientations that results in a
universal curve only in the isotropic case. The deviation from the universal
curve can be used as a complementary means of quantifying the anisotropy by
direct comparison with the solution of our generalized model. Finally, we
applied our model to graphene devices and find that the spin relaxation for
graphene on silicon oxide is isotropic within our experimental resolution
Investigating the spin-orbit interaction in van der Waals heterostructures by means of the spin relaxation anisotropy
Graphene offers long spin propagation and, at the same time, a versatile platform to engineer its physical properties. Proximity-induced phenomena, taking advantage of materials with large spin-orbit coupling or that are magnetic, can be used to imprint graphene with large spin-orbit coupling and magnetic correlations. However, full understanding of the proximitized graphene and the consequences on the spin transport dynamics requires the development of unconventional experimental approaches. The investigation of the spin relaxation anisotropy, defined as the ratio of lifetimes for spins pointing out of and in the graphene plane, is an important step in this direction. This review discusses various methods for extracting the spin relaxation anisotropy in graphene-based devices. Within the experimental framework, current understanding on spin transport dynamics in single-layer and bilayer graphene is presented. Due to increasing interest, experimental results in graphene in proximity with high spin-orbit layered materials are also reviewed
Electrical detection of spin accumulation and spin precession at room temperature in metallic spin valves
We have fabricated a multiterminal lateral mesoscopic metallic spin valve demonstrating spin precession at room temperature (RT), using tunnel barriers in combination with metallic ferromagnetic electrodes as a spin injector and detector. The observed modulation of the output signal due to the spin precession is discussed and explained in terms of a time-of-flight experiment of electrons in a diffusive conductor. The obtained spin relaxation length lambda(sf)=500 nm in an aluminum strip will make detailed studies of spin dependent transport phenomena possible and allow one to explore the possibilities of the electron spin for-new electronic applications at RT. (C) 2002 American Institute of Physics. [DOI: 10.1063/1.1532753].</p
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