56 research outputs found
Thermal Creation of Electron Spin Polarization in n-Type Silicon
Conversion of heat into a spin-current in electron doped silicon can offer a
promising path for spin-caloritronics. Here we create an electron spin
polarization in the conduction band of n-type silicon by producing a
temperature gradient across a ferromagnetic tunnel contact. The substrate
heating experiments induce a large spin signal of 95 V, corresponding to
0.54 meV spin-splitting in the conduction band of n-type silicon by Seebeck
spin tunneling mechanism. The thermal origin of the spin injection has been
confirmed by the quadratic scaling of the spin signal with the Joule heating
current and linear dependence with the heating power
Efficient Spin Injection into Silicon and the Role of the Schottky Barrier
Implementing spin functionalities in Si, and understanding the fundamental
processes of spin injection and detection, are the main challenges in
spintronics. Here we demonstrate large spin polarizations at room temperature,
34% in n-type and 10% in p-type degenerate Si bands, using a narrow Schottky
and a SiO2 tunnel barrier in a direct tunneling regime. Furthermore, by
increasing the width of the Schottky barrier in non-degenerate p-type Si, we
observed a systematic sign reversal of the Hanle signal in the low bias regime.
This dramatic change in the spin injection and detection processes with
increased Schottky barrier resistance may be due to a decoupling of the spins
in the interface states from the bulk band of Si, yielding a transition from a
direct to a localized state assisted tunneling. Our study provides a deeper
insight into the spin transport phenomenon, which should be considered for
electrical spin injection into any semiconductor
Two-Dimensional Spintronic Circuit Architectures on Large Scale Graphene
Solid-state electronics based on utilizing the electron spin degree of
freedom for storing and processing information can pave the way for
next-generation spin-based computing. However, the realization of spin
communication between multiple devices in complex spin circuit geometries,
essential for practical applications, is still lacking. Here, we demonstrate
the spin current propagation in two-dimensional (2D) circuit architectures
consisting of multiple devices and configurations using a large area CVD
graphene on SiO2/Si substrate at room temperature. Taking advantage of the
significant spin transport distance reaching 34 {\mu}m in commercially
available wafer-scale graphene grown on Cu foil, we demonstrate that the spin
current can be effectively communicated between the magnetic memory elements in
graphene channels within 2D circuits of Y-junction and Hexa-arm architectures.
We further show that by designing graphene channels and ferromagnetic elements
at different geometrical angles, the symmetric and antisymmetric components of
the Hanle spin precession signal can be remarkably controlled. These findings
lay the foundation for the design of complex 2D spintronic circuits, which can
be integrated into efficient electronics based on the transport of pure spin
currents
Disorder is not always bad for charge-to-spin conversion in WTe2
The Wang group at Stanford University demonstrates disordered WTex films for efficient charge-to-spin conversion phenomena. The deposition of these films by sputtering and the charge-to-spin conversion resilience against disorder make them attractive for applications in new magnetic memory devices
Gate-tunable Hall sensors on large area CVD graphene protected by h-BN with 1D edge contacts
Graphene is an excellent material for Hall sensors due to its atomically thin
structure, high carrier mobility and low carrier density. However, graphene
devices need to be protected from the environment for reliable and durable
performance in different environmental conditions. Here we present magnetic
Hall sensors fabricated on large area commercially available CVD graphene
protected by exfoliated hexagonal boron nitride (h-BN). To connect the graphene
active regions of Hall samples to the outputs the 1D edge contacts were
utilized which show reliable and stable electrical properties. The operation of
the Hall sensors shows the current-related sensitivity up to 345 V/(AT). By
changing the carrier concentration and type in graphene by the application of
gate voltage we are able to tune the Hall sensitivity
Room Temperature Electrical Detection of Spin Polarized Currents in Topological Insulators
Topological insulators (TIs) are a new class of quantum materials that
exhibit spin momentum locking (SML) of massless Dirac fermions in the surface
states. Usually optical methods, such as angle and spin-resolved photoemission
spectroscopy, have been employed to observe the helical spin polarization in
the surface states of three-dimensional (3D) TIs up to room temperatures.
Recently, spin polarized surface currents in 3D TIs were detected by electrical
methods using ferromagnetic (FM) contacts in a lateral spin-valve measurement
geometry. However, probing the spin texture with such electrical approaches is
so far limited to temperatures below 125K, which restricts its application
potential. Here we demonstrate the room temperature electrical detection of the
spin polarization on the surface of BiSe due to SML by employing spin
sensitive FM tunnel contacts. The current-induced spin polarization on the
BiSe surface is probed at room temperature by measuring a spin-valve
signal while switching the magnetization direction of the FM detector. The spin
signal increases linearly with current bias, reverses sign with current
direction, exhibits a weak temperature dependence and decreases with higher TI
thickness, as predicted theoretically. Our results demonstrate the electrical
detection of the spin polarization on the surface of 3D TIs, which could lead
to innovative spin-based quantum information technology at ambient
temperatures.Comment: Incl. Supplementary informatio
Gate-tunable Spin-Galvanic Effect in Graphene Topological insulator van der Waals Heterostructures at Room Temperature
Unique electronic spin textures in topological states of matter are promising
for emerging spin-orbit driven memory and logic technologies. However, there
are several challenges related to the enhancement of their performance,
electrical gate-tunability, interference from trivial bulk states, and
heterostructure interfaces. We address these challenges by integrating
two-dimensional graphene with a three-dimensional topological insulator (TI) in
van der Waals heterostructures to take advantage of their remarkable spintronic
properties and engineer proximity-induced spin-charge conversion phenomena. In
these heterostructures, we experimentally demonstrate a gate tunable
spin-galvanic effect (SGE) at room temperature, allowing for efficient
conversion of a nonequilibrium spin polarization into a transverse charge
current. Systematic measurements of SGE in various device geometries via a spin
switch, spin precession, and magnetization rotation experiments establish the
robustness of spin-charge conversion in the Gr-TI heterostructures.
Importantly, using a gate voltage, we reveal a strong electric field tunability
of both amplitude and sign of the spin-galvanic signal. These findings provide
an efficient route for realizing all-electrical and gate-tunable spin-orbit
technology using TIs and graphene in heterostructures, which can enhance the
performance and reduce power dissipation in spintronic circuits
Inversion of Spin Signal and Spin Filtering in Ferromagnet|Hexagonal Boron Nitride-Graphene van der Waals Heterostructures
Two dimensional atomically thin crystals of graphene and its insulating isomorph hexagonal boron nitride (h-BN) are promising materials for spintronic applications. While graphene is an ideal medium for long distance spin transport, h-BN is an insulating tunnel barrier that has potential for efficient spin polarized tunneling from ferromagnets. Here, we demonstrate the spin filtering effect in cobalt|few layer h-BN|graphene junctions leading to a large negative spin polarization in graphene at room temperature. Through nonlocal pure spin transport and Hanle precession measurements performed on devices with different interface barrier conditions, we associate the negative spin polarization with high resistance few layer h-BN|ferromagnet contacts. Detailed bias and gate dependent measurements reinforce the robustness of the effect in our devices. These spintronic effects in two-dimensional van der Waals heterostructures hold promise for future spin based logic and memory applications
Charge-spin conversion signal in WTe2 van der Waals hybrid devices with a geometrical design
The efficient generation and control of spin polarization via charge-spin
conversion in topological semimetals are desirable for future spintronic and
quantum technologies. Here, we report the charge-spin conversion (CSC) signals
measured in a Weyl semimetal candidate WTe2 based hybrid graphene device with a
geometrical design. Notably, the geometrical angle of WTe2 on the graphene
spin-valve channel yields contributions to symmetric and anti-symmetric CSC
signal components. The spin precession measurements of CSC signal at different
gate voltages and ferromagnet magnetization shows the robustness of the CSC in
WTe2 at room temperature. These results can be useful for the design of
heterostructure devices and in the architectures of two-dimensional spintronic
circuits
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