118 research outputs found
Temperature dependence of spin diffusion length and spin Hall angle in Au and Pt
We have studied the spin transport and the spin Hall effect as a function of
temperature for platinum (Pt) and gold (Au) in lateral spin valve structures.
First, by using the spin absorption technique, we extract the spin diffusion
length of Pt and Au. Secondly, using the same devices, we have measured the
spin Hall conductivity and analyzed its evolution with temperature to identify
the dominant scattering mechanisms behind the spin Hall effect. This analysis
confirms that the intrinsic mechanism dominates in Pt whereas extrinsic effects
are more relevant in Au. Moreover, we identify and quantify the phonon-induced
skew scattering. We show that this contribution to skew scattering becomes
relevant in metals such as Au, with a low residual resistivity.Comment: 13 pages, 5 figure
Scale-invariant large nonlocality in polycrystalline graphene
The observation of large nonlocal resistances near the Dirac point in
graphene has been related to a variety of intrinsic Hall effects, where the
spin or valley degrees of freedom are controlled by symmetry breaking
mechanisms. Engineering strong spin or valley Hall signals on scalable graphene
devices could stimulate further practical developments of spin- and
valleytronics. Here we report on scale-invariant nonlocal transport in
large-scale chemical vapour deposition graphene under an applied external
magnetic field. Contrary to previously reported Zeeman spin Hall effect, our
results are explained by field-induced spin-filtered edge states whose
sensitivity to grain boundaries manifests in the nonlocal resistance. This
phenomenon, related to the emergence of the quantum Hall regime, persists up to
the millimeter scale, showing that polycrystalline morphology can be imprinted
in nonlocal transport. This suggests that topological Hall effects in
large-scale graphene materials are highly sensitive to the underlying
structural morphology, limiting practical realizations.Comment: Main paper (14 pages, 5 figures) and Supplementary information (8
pages, 8 figures
How reliable are Hanle measurements in metals in a three-terminal geometry?
We test the validity of Hanle measurements in three-terminal devices by using
aluminum (Al) and gold (Au). The obtained Hanle and inverted Hanle-like curves
show an anomalous behavior. First, we measure Hanle signals 8 orders of
magnitude larger than those predicted by standard theory. Second, the
temperature and voltage dependences of the signal do not match with the
tunneling spin polarization of the ferromagnetic contact. Finally, the spin
relaxation times obtained with this method are independent of the choice of the
metallic channel. These results are not compatible with spin accumulation in
the metal. Furthermore, a scaling of the Hanle signal with the interface
resistance of the devices suggests that the measured signal is originated in
the tunnel junction.Comment: 9 pages, 5 figure
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