148 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
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
Spin current induced magnetization oscillations in a paramagnetic disc
When electron spins are injected uniformly into a paramagnetic disc, they can
precess along the demagnetizing field induced by the resulting magnetic moment.
Normally this precession damps out by virtue of the spin relaxation which is
present in paramagnetic materials. We propose a new mechanism to excite a
steady-state form of this dynamics by injecting a constant spin current into
this paramagnetic disc. We show that the rotating magnetic field generated by
the eddy currents provide a torque which makes this possible. Unlike the
ferromagnetic equivalent, the spin-torque-oscillator, the oscillation frequency
is fixed and determined by the dimensions and intrinsic parameters of the
paramagnet. The system possesses an intrinsic threshold for spin injection
which needs to be overcome before steady-state precession is possible. The
additional application of a magnetic field lowers this threshold. We discuss
the feasibility of this effect in modern materials. Transient analysis using
pump-probe techniques should give insight in the physical processes which
accompany this effect
Spin transport in high-mobility graphene on WS2 substrate with electric-field tunable proximity spin-orbit interaction
Graphene supported on a transition metal dichalcogenide substrate offers a
novel platform to study the spin transport in graphene in presence of a
substrate induced spin-orbit coupling, while preserving its intrinsic charge
transport properties. We report the first non-local spin transport measurements
in graphene completely supported on a 3.5 nm thick tungsten disulfide (WS)
substrate, and encapsulated from the top with a 8 nm thick hexagonal boron
nitride layer. For graphene, having mobility up to 16,000
cmVs, we measure almost constant spin-signals both in
electron and hole-doped regimes, independent of the conducting state of the
underlying WS substrate, which rules out the role of spin-absorption by
WS. The spin-relaxation time for the electrons in
graphene-on-WS is drastically reduced down to~10 ps than
~ 800 ps in graphene-on-SiO on the same chip. The strong suppression of
along with a detectable weak anti-localization signature in
the quantum magneto-resistance measurements is a clear effect of the WS
induced spin-orbit coupling (SOC) in graphene. Via the top-gate voltage
application in the encapsulated region, we modulate the electric field by 1
V/nm, changing almost by a factor of four which suggests the
electric-field control of the in-plane Rashba SOC. Further, via carrier-density
dependence of we also identify the fingerprints of the
D'yakonov-Perel' type mechanism in the hole-doped regime at the graphene-WS
interface.Comment: 11 pages, 7 figure
Spin-Dependent Electron Transmission Model for Chiral Molecules in Mesoscopic Devices
Various device-based experiments have indicated that electron transfer in
certain chiral molecules may be spin-dependent, a phenomenon known as the
Chiral Induced Spin Selectivity (CISS) effect. However, due to the complexity
of these devices and a lack of theoretical understanding, it is not always
clear to what extent the chiral character of the molecules actually contributes
to the magnetic-field-dependent signals in these experiments. To address this
issue, we report here an electron transmission model that evaluates the role of
the CISS effect in two-terminal and multi-terminal linear-regime electron
transport experiments. Our model reveals that for the CISS effect, the
chirality-dependent spin transmission is accompanied by a spin-flip electron
reflection process. Furthermore, we show that more than two terminals are
required in order to probe the CISS effect in the linear regime. In addition,
we propose two types of multi-terminal nonlocal transport measurements that can
distinguish the CISS effect from other magnetic-field-dependent signals. Our
model provides an effective tool to review and design CISS-related transport
experiments, and to enlighten the mechanism of the CISS effect itself
Linear-response magnetoresistance effects in chiral systems
The chirality-induced spin selectivity (CISS) effect enables the detection of
chirality as electrical charge signals. It is often studied using a
two-terminal circuit geometry where a ferromagnet is connected to a chiral
component, and a change of electrical resistance is reported upon magnetization
reversal. This is however not expected in the linear response regime because of
compensating reciprocal processes, limiting the interpretation of experimental
results. Here we show that magnetoresistance effects can indeed appear even in
the linear response regime, either by changing the magnitude or the direction
of the magnetization or an applied magnetic field. We illustrate this in a
spin-valve device and in a chiral thin film as the CISS-induced Hanle
magnetoresistance (CHMR) effect. This effect helps to distinguish
spin-transport-related effects from other effects, and can thereby provide
further insight into the origin of CISS
Circuit-Model Analysis for Spintronic Devices with Chiral Molecules as Spin Injectors
Recent research discovered that charge transfer processes in chiral molecules
can be spin selective and named the effect chiral-induced spin selectivity
(CISS). Follow-up work studied hybrid spintronic devices with conventional
electronic materials and chiral (bio)molecules. However, a theoretical
foundation for the CISS effect is still in development and the spintronic
signals were not evaluated quantitatively. We present a circuit-model approach
that can provide quantitative evaluations. Our analysis assumes the scheme of a
recent experiment that used photosystem~I (PSI) as spin injectors, for which we
find that the experimentally observed signals are, under any reasonable
assumptions on relevant PSI time scales, too high to be fully due to the CISS
effect. We also show that the CISS effect can in principle be detected using
the same type of solid-state device, and by replacing silver with graphene, the
signals due to spin generation can be enlarged four orders of magnitude. Our
approach thus provides a generic framework for analyzing this type of
experiments and advancing the understanding of the CISS effect
Platinum thickness dependence of the inverse spin-Hall voltage from spin pumping in a hybrid YIG/Pt system
We show the first experimental observation of the platinum (Pt) thickness
dependence in a hybrid YIG/Pt system of the inverse spin-Hall effect from spin
pumping, over a large frequency range and for different rf powers. From the
measurement of the dc voltage () at the resonant condition
and the resistance () of the Pt layer, a strong enhancement of the ratio
has been observed, which is not in agreement with previous
studies on the NiFe/Pt system. The origin of this behaviour is still unclear
and cannot be explained by the spin transport model that we have used.Comment: 4 pages, 3 figure
- β¦