1,993 research outputs found
Chiral magnetoresistance in Pt/Co/Pt zigzag wires
The Rashba effect leads to a chiral precession of the spins of moving
electrons while the Dzyaloshinskii-Moriya interaction (DMI) generates
preference towards a chiral profile of local spins. We predict that the
exchange interaction between these two spin systems results in a 'chiral'
magnetoresistance depending on the chirality of the local spin texture. We
observe this magnetoresistance by measuring the domain wall (DW) resistance in
a uniquely designed Pt/Co/Pt zigzag wire, and by changing the chirality of the
DW with applying an in-plane magnetic field. A chirality-dependent DW
resistance is found, and a quantitative analysis shows a good agreement with a
theory based on the Rashba model. Moreover, the DW resistance measurement
allows us to independently determine the strength of the Rashba effect and the
DMI simultaneously, and the result implies a possible correlation between the
Rashba effect, the DMI, and the symmetric Heisenberg exchange
Observation of Spin Hall Effect in Weyl Semimetal WTe2 at Room Temperature
Discovery of topological Weyl semimetals has revealed the opportunities to
realize several extraordinary physical phenomena in condensed matter physics.
Specifically, these semimetals with strong spin-orbit coupling, broken
inversion symmetry and novel spin texture are predicted to exhibit a large spin
Hall effect that can efficiently convert the charge current to a spin current.
Here we report the direct experimental observation of a large spin Hall and
inverse spin Hall effects in Weyl semimetal WTe2 at room temperature obeying
Onsager reciprocity relation. We demonstrate the detection of the pure spin
current generated by spin Hall phenomenon in WTe2 by making van der Waals
heterostructures with graphene, taking advantage of its long spin coherence
length and spin transmission at the heterostructure interface. These
experimental findings well supported by ab initio calculations show a large
charge-spin conversion efficiency in WTe2; which can pave the way for
utilization of spin-orbit induced phenomena in spintronic memory and logic
circuit architectures
Chirality-induced asymmetric magnetic nucleation in Pt/Co/AlOx ultrathin microstructures
The nucleation of reversed magnetic domains in Pt/Co/AlO
microstructures with perpendicular anisotropy was studied experimentally in the
presence of an in-plane magnetic field. For large enough in-plane field,
nucleation was observed preferentially at an edge of the sample normal to this
field. The position at which nucleation takes place was observed to depend in a
chiral way on the initial magnetization and applied field directions. An
explanation of these results is proposed, based on the existence of a sizable
Dzyaloshinskii-Moriya interaction in this sample. Another consequence of this
interaction is that the energy of domain walls can become negative for in-plane
fields smaller than the effective anisotropy field.Comment: Published version, Physical Review Letters 113, 047203 (2014
Magnonic Quadrupole Topological Insulator in Antiskyrmion Crystals
When the crystalline symmetries that protect a higher-order topological phase
are not preserved at the boundaries of the sample, gapless hinge modes or
in-gap corner states cannot be stabilized. Therefore, careful engineering of
the sample termination is required. Similarly, magnetic textures, whose quantum
fluctuations determine the supported magnonic excitations, tend to relax to new
configurations that may also break crystalline symmetries when boundaries are
introduced. Here we uncover that antiskyrmion crystals provide an
experimentally accessible platform to realize a magnonic topological quadrupole
insulator, whose hallmark signature are robust magnonic corner states.
Furthermore, we show that tuning an applied magnetic field can trigger the
self-assembly of antiskyrmions carrying a fractional topological charge along
the sample edges. Crucially, these fractional antiskyrmions restore the
symmetries needed to enforce the emergence of the magnonic corner states. Using
the machinery of nested Wilson loops, adapted to magnonic systems supported by
noncollinear magnetic textures, we demonstrate the quantization of the bulk
quadrupole moment, edge dipole moments, and corner charges
Quantitative magneto-optical investigation of superconductor/ferromagnet hybrid structures
We present a detailed quantitative magneto-optical imaging study of several
superconductor/ferromagnet hybrid structures, including Nb deposited on top of
thermomagnetically patterned NdFeB, and permalloy/niobium with erasable and
tailored magnetic landscapes imprinted in the permalloy layer. The
magneto-optical imaging data is complemented with and compared to scanning Hall
probe microscopy measurements. Comprehensive protocols have been developed for
calibrating, testing, and converting Faraday rotation data to magnetic field
maps. Applied to the acquired data, they reveal the comparatively weaker
magnetic response of the superconductor from the background of larger fields
and field gradients generated by the magnetic layer.Comment: 21 pages, including 2 pages of supplementary materia
Tuning magnetic chirality by dipolar interactions
Chiral magnetism has gained enormous interest in recent years because of the
anticipated wealth of applications in nanoelectronics. The demonstrated
stabilization of chiral magnetic domain walls and skyrmions has been attributed
to the actively investigated Dzyaloshinskii-Moriya interaction. Recently,
however, predictions were made that suggest dipolar interactions can also
stabilize chiral domain walls and skyrmions, but direct experimental evidence
has been lacking. Here we show that dipolar interactions can indeed stabilize
chiral domain walls by directly imaging the magnetic domain walls using
scanning electron microscopy with polarization analysis. We further show that
the competition between the Dzyaloshinskii-Moriya and dipolar interactions can
reverse the domain-wall chirality. Finally, we suggest that this competition
can be tailored by a Ruderman-Kittel-Kasuya-Yosida interaction. Our work
therefore reveals that dipolar interactions play a key role in the
stabilization of chiral spin textures. This insight will open up new routes
towards balancing interactions for the stabilization of chiral magnetism
- …