835 research outputs found
Magnetic field control of the spin Seebeck effect
The origin of the suppression of the longitudinal spin Seebeck effect by
applied magnetic fields is studied. We perform numerical simulations of the
stochastic Landau-Lifshitz-Gilbert equation of motion for an atomistic spin
model and calculate the magnon accumulation in linear temperature gradients for
different strengths of applied magnetic fields and different length scales of
the temperature gradient. We observe a decrease of the magnon accumulation with
increasing magnetic field and we reveal that the origin of this effect is a
field dependent change of the frequency distribution of the propagating
magnons. With increasing field the magnonic spin currents are reduced due to a
suppression of parts of the frequency spectrum. By comparison with measurements
of the magnetic field dependent longitudinal spin Seebeck effect in YIG thin
films with various thicknesses, we find that our model describes the
experimental data very well, demonstrating the importance of this effect for
experimental systems
Thermal generation of spin current in epitaxial CoFe2O4 thin films
The longitudinal spin Seebeck effect (LSSE) has been investigated in
high-quality epitaxial CoFe2O4 (CFO) thin films. The thermally excited spin
currents in the CFO films are electrically detected in adjacent Pt layers due
to the inverse spin Hall effect (ISHE). The LSSE signal exhibits a linear
increase with increasing temperature gradient, yielding a LSSE coefficient of
~100 nV/K at room temperature. The temperature dependence of the LSSE is
investigated from room temperature down to 30 K, showing a significant
reduction at low temperatures, revealing that the total amount of thermally
generated magnons decreases. Furthermore, we demonstrate that the spin Seebeck
effect is an effective tool to study the magnetic anisotropy induced by
epitaxial strain, especially in ultrathin films with low magnetic moments.Comment: 17 pages, 4 figure
Influence of thickness and interface on the low-temperature enhancement of the spin Seebeck effect in YIG films
The temperature dependent longitudinal spin Seebeck effect (LSSE) in heavy metal (HM)/Y3Fe5O12 (YIG) hybrid structures is investigated as a function of YIG film thickness, magnetic field strength, and different HM detection material. The LSSE signal shows a large enhancement with reducing the temperature, leading to a pronounced peak at low temperatures. We find the LSSE peak temperature strongly depends on the film thickness as well as on the magnetic field. Our result can be well explained in the framework of magnon-driven LSSE by taking into account the temperature dependent effective propagation length of thermally excited magnons in bulk. We further demonstrate that the LSSE peak is significantly shifted by changing the interface coupling to an adjacent detection layer, revealing a more complex behavior beyond the currently discussed bulk effect. By direct microscopic imaging of the interface, we correlate the observed temperature dependence with the interface structure between the YIG and the adjacent metal layer. Our results highlight the role of interface effects on the temperature dependent LSSE in HM/YIG system, suggesting that the temperature dependent spin current transparency strikingly relies on the interface conditions
Janus Monolayer Transition Metal Dichalcogenides
A novel crystal configuration of sandwiched S-Mo-Se structure (Janus SMoSe)
at the monolayer limit has been synthesized and carefully characterized in this
work. By controlled sulfurization of monolayer MoSe2 the top layer of selenium
atoms are substituted by sulfur atoms while the bottom selenium layer remains
intact. The peculiar structure of this new material is systematically
investigated by Raman, photoluminescence and X-ray photoelectron spectroscopy
and confirmed by transmission-electron microscopy and time-of-flight secondary
ion mass spectrometry. Density-functional theory calculations are performed to
better understand the Raman vibration modes and electronic structures of the
Janus SMoSe monolayer, which are found to correlate well with corresponding
experimental results. Finally, high basal plane hydrogen evolution reaction
(HER) activity is discovered for the Janus monolayer and DFT calculation
implies that the activity originates from the synergistic effect of the
intrinsic defects and structural strain inherent in the Janus structure.Comment: 22 pages, 12 figure
Dimensionality-confined superconductivity within SrNbO3-SrTiO3 heterostructures
Interfaces between transition-metal oxides are able to host two-dimensional
electron gases (2DEGs) and exhibit exotic quantum phenomena. Here we report the
observation of superconductivity below 230 mK for the heterostructure composed
of SrNbO3 (SNO) and SrTiO3 (STO). Different from some other counterparts with
two insulators, the metallic SNO provides a novel mechanism to form a quasi
2DEG by charge transfer from bulk towards interface under strain. The
superconductivity, residing within the strained SNO layer near the interface,
is contributed by an electron system with record-low carrier density. Notably,
although embedded in a normal metallic layer with a carrier density 4 to 5
orders higher, the electron system is still uniquely well-protected to retain
high mobility and lies deep in extreme quantum regime
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