1,541 research outputs found
Graphene-WS heterostructures for tunable spin injection and spin transport
We report the first measurements of spin injection in to graphene through a
20 nm thick tungsten disulphide (WS) layer, along with a modified spin
relaxation time ({\tau}s) in graphene in the WS environment, via spin-valve
and Hanle spin-precession measurements, respectively. First, during the
spin-injection into graphene through a WS-graphene interface, we can tune
the interface resistance at different current bias and modify the spin
injection efficiency, in a correlation with the conductivity-mismatch theory.
Temperature assisted tunneling is identified as a dominant mechanism for the
charge transport across the interface. Second, we measure the spin transport in
graphene, underneath the WS crystal and observe a significant reduction in
the {\tau}s down to 17 ps in graphene in the WS covered region, compared to
that in its pristine state. The reduced {\tau}s indicates the WS-proximity
induced additional dephasing of the spins in graphene.Comment: 7 Pages, 6 figure
Observation of anomalous Hanle spin precession lineshapes resulting from interaction with localized states
It has been shown recently that in spin precession experiments, the
interaction of spins with localized states can change the response to a
magnetic field, leading to a modified, effective spin relaxation time and
precession frequency. Here, we show that also the shape of the Hanle curve can
change, so that it cannot be fitted with the solutions of the conventional
Bloch equation. We present experimental data that shows such an effect arising
at low temperatures in epitaxial graphene on silicon carbide with localized
states in the carbon buffer layer. We compare the strength of the effect
between materials with different growth methods, epitaxial growth by
sublimation and by chemical vapor deposition. The presented analysis gives
information about the density of localized states and their coupling to the
graphene states, which is inaccessible by charge transport measurements and can
be applied to any spin transport channel that is coupled to localized states.Comment: 6 pages, 6 figure
Separating spin and charge transport in single wall carbon nanotubes
We demonstrate spin injection and detection in single wall carbon nanotubes
using a 4-terminal, non-local geometry. This measurement geometry completely
separates the charge and spin circuits. Hence all spurious magnetoresistance
effects are eliminated and the measured signal is due to spin accumulation
only. Combining our results with a theoretical model, we deduce a spin
polarization at the contacts of approximately 25 %. We show that the
magnetoresistance changes measured in the conventional two-terminal geometry
are dominated by effects not related to spin accumulation.Comment: Number of pages: 11 Number of figures:
Verification of the Thomson-Onsager reciprocity relation for spin caloritronics
We investigate the Thomson-Onsager relation between the spin-dependent
Seebeck and spin-dependent Peltier effect. To maintain identical device and
measurement conditions we measure both effects in a single
NiFe/Cu/NiFe nanopillar spin valve device subjected
to either an electrical or a thermal bias. In the low bias regime, we observe
similar spin signals as well as background responses, as required by the
Onsager reciprocity relation. However, at large biases, deviation from
reciprocity occurs due to dominant nonlinear contribution of the temperature
dependent transport coefficients. By systematic modeling of these nonlinear
thermoelectric effects and measuring higher order thermoelectric responses for
different applied biases, we identify the transition between the two regimes as
the point at which Joule heating start to dominate over Peltier heating. Our
results signify the importance of local equilibrium for the validity of this
phenomenological reciprocity relation.Comment: 5 pages, 5 figure
The Magneto-coulomb effect in spin valve devices
We discuss the influence of the magneto-coulomb effect (MCE) on the
magnetoconductance of spin valve devices. We show that MCE can induce
magnetoconductances of several per cents or more, dependent on the strength of
the coulomb blockade. Furthermore, the MCE-induced magnetoconductance changes
sign as a function of gate voltage. We emphasize the importance of separating
conductance changes induced by MCE from those due to spin accumulation in spin
valve devices.Comment: This paper includes 3 figure
Electrical spin injection, transport, and detection in graphene-hexagonal boron nitride van der Waals heterostructures: progress and perspectives
The current research in graphene spintronics strives for achieving a long
spin lifetime, and efficient spin injection and detection in graphene. In this
article, we review how hexagonal boron nitride (hBN) has evolved as a crucial
substrate, as an encapsulation layer, and as a tunnel barrier for manipulation
and control of spin lifetimes and spin injection/detection polarizations in
graphene spin valve devices. First, we give an overview of the challenges due
to conventional SiO substrate for spin transport in graphene followed by
the progress made in hBN based graphene heterostructures. Then we discuss in
detail the shortcomings and developments in using conventional oxide tunnel
barriers for spin injection into graphene followed by introducing the recent
advancements in using the crystalline single/bi/tri-layer hBN tunnel barriers
for an improved spin injection and detection which also can facilitate
two-terminal spin valve and Hanle measurements, at room temperature, and are of
technological importance. A special case of bias induced spin polarization of
contacts with exfoliated and chemical vapour deposition (CVD) grown hBN tunnel
barriers is also discussed. Further, we give our perspectives on utilizing
graphene-hBN heterostructures for future developments in graphene spintronics.Comment: Review, Author submitted manuscript - draft; 25 pages, 8 figure
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