4,628 research outputs found
Spin accumulation and dynamics in inversion-symmetric van der Waals crystals
Inversion symmetric materials are forbidden to show an overall spin texture
in their band structure in the presence of time-reversal symmetry. However, in
van der Waals materials which lack inversion symmetry within a single layer, it
has been proposed that a layer-dependent spin texture can arise leading to a
coupled spin-layer degree of freedom. Here we use time-resolved Kerr rotation
in inversion symmetric WSe and MoSe bulk crystals to study this
spin-layer polarization and unveil its dynamics. Our measurements show that the
spin-layer relaxation time in WSe is limited by phonon-scattering at high
temperatures and that the inter-layer hopping can be tunned by a small in-plane
magnetic field at low temperatures, enhancing the relaxation rates. We find a
significantly lower lifetime for MoSe which agrees with theoretical
expectations of a spin-layer polarization stabilized by the larger spin-orbit
coupling in WSe
Thickness dependence of spin-orbit torques generated by WTe2
We study current-induced torques in WTe2/permalloy bilayers as a function of
WTe2 thickness. We measure the torques using both second-harmonic Hall and
spin-torque ferromagnetic resonance measurements for samples with WTe2
thicknesses that span from 16 nm down to a single monolayer. We confirm the
existence of an out-of-plane antidamping torque, and show directly that the
sign of this torque component is reversed across a monolayer step in the WTe2.
The magnitude of the out-of-plane antidamping torque depends only weakly on
WTe2 thickness, such that even a single-monolayer WTe2 device provides a strong
torque that is comparable to much thicker samples. In contrast, the
out-of-plane field-like torque has a significant dependence on the WTe2
thickness. We demonstrate that this field-like component originates
predominantly from the Oersted field, thereby correcting a previous inference
drawn by our group based on a more limited set of samples.Comment: 8 pages, 8 figure
Large interfacial spin-orbit torques in layered antiferromagnetic insulator NiPS3/ferromagnet bilayers
Finding efficient ways of manipulating magnetic bits is one of the core goals
in spintronic research. Electrically-generated spin-orbit torques (SOTs) are
good candidates for this and the search for materials capable of generating
highly-efficient SOTs has gained a lot of traction in the recent years. While
antiferromagnet/ferromagnet bilayer structures have been employed extensively
for passive applications, e.g. by using exchange bias fields, their active
properties are not yet widely employed. Here we show the presence of large
interfacial SOTs in bilayer of a ferromagnet and the two-dimensional layered
antiferromagnetic insulator NiPS. We observe a large in-plane damping-like
interfacial torque, showing a torque conductivity of even at room
temperature, comparable to the best devices reported in the literature for
standard heavy-metal-based and topological insulators-based devices.
Additionally, our devices also show an out-of-plane field-like torque arising
from the NiPS/ferromagnet interface, further indicating the presence of an
interfacial spin-orbit coupling in our structures. Temperature-dependent
measurements reveal an increase of the SOTs with a decreasing temperature below
the N\'eel temperature of NiPS (), pointing to
a possible effect of the magnetic ordering on our measured SOTs. Our findings
show the potential of antiferromagnetic insulators and two-dimensional
materials for future spintronic applications.Comment: 19 pages, 3 figures, 1 table. Changed units of the torque normalized
by the electric field from to $\mathrm{nm \, T/V}
Layer effects on the magnetic textures in magnets with local inversion asymmetry
Magnets with broken local inversion symmetries are interesting candidates for
chiral magnetic textures such as skyrmions and spin spirals. The property of
these magnets is that each subsequent layer can possess a different
Dzyaloshniskii-Moriya interaction (DMI) originating from the local inversion
symmetry breaking. Given that new candidates of such systems are emerging, with
the Van der Waals crystals and magnetic multilayer systems, it is interesting
to investigate how the chiral magnetic textures depend on the number of layers
and the coupling between them. In this article, we model the magnetic layers
with a classical Heisenberg spin model, where the sign of the DMI alternates
for each consecutive layer. We use Monte Carlo simulations to examine chiral
magnetic textures and show that the pitch of magnetic spirals is influenced by
the interlayer coupling and the number of layers. We observe even-odd effects
in the number of layers, where we observe a suppression of the spin spirals for
even layer numbers. We give an explanation for our findings by proposing a net
DMI in systems with strongly coupled layers. Our results can be used to
determine the DMI in systems with a known number of layers, and for new
technologies based on the tunability of the spiral wave length.Comment: 8 pages, 8 figures and 2 table
Neutron Transfer reactions induced by 8Li on 9Be
Angular distributions for the elastic scattering of 8Li on 9Be and the
neutron transfer reactions 9Be(8Li,7Li)10Be and 9Be(8Li,9Li)8Be have been
measured with a 27 MeV 8Li radioactive nuclear beam. Spectroscopic factors for
8Li|n=9Li and 7Li|n=8Li bound systems were obtained from the comparison between
the experimental differential cross section and finite-range DWBA calculations
with the code FRESCO. The spectroscopic factors obtained are compared to shell
model calculations and to other experimental values from (d,p) reactions. Using
the present values for the spectroscopic factor, cross sections for the direct
neutron-capture reactions 7Li(n,g)8Li and 8Li(n,g)9Li were calculated in the
framework of a potential model.Comment: 24 pages, 8 Figures, submitted as regular article to PR
Control of polarization and mode mapping of small volume high Q micropillars
We show that the polarization of the emission of a single quantum dot embedded within a microcavity pillar of elliptical cross section can be completely controlled and even switched between two orthogonal linear polarizations by changing the coupling of the dot emission with the polarized photonic modes. We also measure the spatial profle of the emission of a series of pillars with
different ellipticities and show that the results can be well described by simple theoretical modeling
of the modes of an infinite length elliptical cylinder
Spin-orbit torques in NbSe/Permalloy bilayers
We present measurements of current-induced spin-orbit torques generated by
NbSe, a fully-metallic transition-metal dichalcogenide material, made using
the spin-torque ferromagnetic resonance (ST-FMR) technique with
NbSe/Permalloy bilayers. In addition to the out-of-plane Oersted torque
expected from current flow in the metallic NbSe layer, we also observe an
in-plane antidamping torque with torque conductivity (m) and indications of a weak field-like
contribution to the out-of-plane torque oriented opposite to the Oersted
torque. Furthermore, in some samples we also measure an in-plane field-like
torque with the form , where is the Permalloy
magnetization direction and is perpendicular to the sample plane. The
size of this component varies strongly between samples and is not correlated
with the NbSe thickness. A torque of this form is not allowed by the bulk
symmetries of NbSe, but is consistent with symmetry breaking by a
uniaxial strain that might result during device fabrication.Comment: 14 pages, 3 figure
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