361 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
All Magnesium diboride Josephson Junctions with MgO and native oxide barriers
We present results on all-MgB2 tunnel junctions, where the tunnel barrier is
deposited MgO or native-oxide of base electrode. For the junctions with MgO,
the hysteretic I-V curve resembles a conventional underdamped Josephson
junction characteristic with critical current-resistance product nearly
independent of the junction area. The dependence of the critical current with
temperature up to 20 K agrees with the [Ambegaokar and Baratoff, Phys. Rev.
Lett. 10, 486 (1963)] expression. For the junctions with native-oxide,
conductance at low bias exhibits subgap features while at high bias reveals
thick barriers. As a result no supercurrent was observed in the latter, despite
the presence of superconducting-gaps to over 30 K.Comment: 8 pages with 3 figure
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
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
Large cone angle magnetization precession of an individual nanomagnet with dc electrical detection
We demonstrate on-chip resonant driving of large cone-angle magnetization
precession of an individual nanoscale permalloy element. Strong driving is
realized by locating the element in close proximity to the shorted end of a
coplanar strip waveguide, which generates a microwave magnetic field. We used a
microwave frequency modulation method to accurately measure resonant changes of
the dc anisotropic magnetoresistance. Precession cone angles up to are
determined with better than one degree of resolution. The resonance peak shape
is well-described by the Landau-Lifshitz-Gilbert equation
A Case of Ciliate Protozoa Colpoda Spp. (Ciliata: Colpodidae) Detected In Human Urine
In the urine of a patient with chronic prostatitis, renal microlithiasis and acute cystitis we found the ciliate protozoa Colpoda spp., both in vegetative and cystic form. The entry point was most likely the urinary tract. Keeping in mind that only four more cases of Colpoda spp. existent in human urine have already been described, and that in the case of our patient the ciliate was present at repeated examinations of his urine, we presumed that it is not only a spurious infection of the urogenital tract. It still remains to be analyzed whether this ciliate belongs to a species of Colpoda adapted to parasitism in homeothermae and whether it can be pathogenic for humans
Electrical detection of spin pumping: dc voltage generated by ferromagnetic resonance at ferromagnet/nonmagnet contact
We describe electrical detection of spin pumping in metallic nanostructures.
In the spin pumping effect, a precessing ferromagnet attached to a normal-metal
acts as a pump of spin-polarized current, giving rise to a spin accumulation.
The resulting spin accumulation induces a backflow of spin current into the
ferromagnet and generates a dc voltage due to the spin dependent conductivities
of the ferromagnet. The magnitude of such voltage is proportional to the
spin-relaxation properties of the normal-metal. By using platinum as a contact
material we observe, in agreement with theory, that the voltage is
significantly reduced as compared to the case when aluminum was used.
Furtheremore, the effects of rectification between the circulating rf currents
and the magnetization precession of the ferromagnet are examined. Most
significantly, we show that using an improved layout device geometry these
effects can be minimized.Comment: 9 pages, 11 figure
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
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
Electrical detection of spin pumping due to the precessing magnetization of a single ferromagnet
We report direct electrical detection of spin pumping, using a lateral normal
metal/ferromagnet/normal metal device, where a single ferromagnet in
ferromagnetic resonance pumps spin polarized electrons into the normal metal,
resulting in spin accumulation. The resulting backflow of spin current into the
ferromagnet generates a d.c. voltage due to the spin dependent conductivities
of the ferromagnet. By comparing different contact materials (Al and /or Pt),
we find, in agreement with theory, that the spin related properties of the
normal metal dictate the magnitude of the d.c. voltage
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