19 research outputs found
Sign of inverse spin Hall voltages generated by ferromagnetic resonance and temperature gradients in yttrium iron garnet|platinum bilayers
We carried out a concerted effort to determine the absolute sign of the
inverse spin Hall effect voltage generated by spin currents injected into a
normal metal. We focus on yttrium iron garnet (YIG)|platinum bilayers at room
temperature, generating spin currents by microwaves and temperature gradients.
We find consistent results for different samples and measurement setups that
agree with theory. We suggest a right-hand-rule to define a positive spin Hall
angle corresponding to with the voltage expected for the simple case of
scattering of free electrons from repulsive Coulomb charges.Comment: incorporated additions from the published versio
Propagating spin-wave spectroscopy in nanometer-thick YIG films at millikelvin temperatures
Performing propagating spin-wave spectroscopy of thin films at millikelvin
temperatures is the next step towards the realisation of large-scale integrated
magnonic circuits for quantum applications. Here we demonstrate spin-wave
propagation in a -thick yttrium-iron-garnet film at the
temperatures down to , using stripline nanoantennas deposited
on YIG surface for the electrical excitation and detection. The clear
transmission characteristics over the distance of are
measured and the subtracted spin-wave group velocity and the YIG saturation
magnetisation agree well with the theoretical values. We show that the
gadolinium-gallium-garnet substrate influences the spin-wave propagation
characteristics only for the applied magnetic fields beyond ,
originating from a GGG magnetisation up to at . Our results show that the developed fabrication and measurement
methodologies enable the realisation of integrated magnonic quantum
nanotechnologies at millikelvin temperatures.Comment: 6 pages, 5 figure
Control of the Bose-Einstein Condensation of Magnons by the Spin-Hall Effect
Previously, it has been shown that rapid cooling of yttrium-iron-garnet
(YIG)/platinum (Pt) nano structures, preheated by an electric current sent
through the Pt layer, leads to overpopulation of a magnon gas and to subsequent
formation of a Bose-Einstein condensate (BEC) of magnons. The spin Hall effect
(SHE), which creates a spin-polarized current in the Pt layer, can inject or
annihilate magnons depending on the electric current and applied field
orientations. Here we demonstrate that the injection or annihilation of magnons
via the SHE can prevent or promote the formation of a rapid cooling induced
magnon BEC. Depending on the current polarity, a change in the BEC threshold of
-8% and +6% was detected. These findings demonstrate a new method to control
macroscopic quantum states, paving the way for their application in spintronic
devices
Stabilization of a nonlinear bullet coexisting with a Bose-Einstein condensate in a rapidly cooled magnonic system driven by a spin-orbit torque
We have recently shown that injection of magnons into a magnetic dielectric
via the spin-orbit torque (SOT) effect in the adjacent layer of a heavy metal
subjected to the action of short (0.1 s) current pulses allows for control
of a magnon Bose-Einstein Condensate (BEC). Here, the BEC was formed in the
process of rapid cooling (RC), when the electric current heating the sample is
abruptly terminated. In the present study, we show that the application of a
longer (1.0 s) electric current pulse triggers the formation of a
nonlinear localized magnonic bullet below the linear magnon spectrum. After
pulse termination, the magnon BEC, as before, is formed at the bottom of the
linear spectrum, but the nonlinear bullet continues to exist, stabilized for
additional 30 ns by the same process of RC-induced magnon condensation. Our
results suggest that a stimulated condensation of excess magnons to all highly
populated magnonic states occurs
BDNF in Lower Brain Parts Modifies Auditory Fiber Activity to Gain Fidelity but Increases the Risk for Generation of Central Noise After Injury
For all sensory organs, the establishment of spatial and temporal cortical resolution is assumed to be initiated by the first sensory experience and a BDNF-dependent increase in intracortical inhibition. To address the potential of cortical BDNF for sound processing, we used mice with a conditional deletion of BDNF in which Cre expression was under the control of the Pax2 or TrkC promoter. BDNF deletion profiles between these mice differ in the organ of Corti (BDNF -KO) versus the auditory cortex and hippocampus (BDNF -KO). We demonstrate that BDNF -KO but not BDNF -KO mice exhibit reduced sound-evoked suprathreshold ABR waves at the level of the auditory nerve (wave I) and inferior colliculus (IC) (wave IV), indicating that BDNF in lower brain regions but not in the auditory cortex improves sound sensitivity during hearing onset. Extracellular recording of IC neurons of BDNF mutant mice revealed that the reduced sensitivity of auditory fibers in these mice went hand in hand with elevated thresholds, reduced dynamic range, prolonged latency, and increased inhibitory strength in IC neurons. Reduced parvalbumin-positive contacts were found in the ascending auditory circuit, including the auditory cortex and hippocampus of BDNF -KO, but not of BDNF -KO mice. Also, BDNF -WT but not BDNF -KO mice did lose basal inhibitory strength in IC neurons after acoustic trauma. These findings suggest that BDNF in the lower parts of the auditory system drives auditory fidelity along the entire ascending pathway up to the cortex by increasing inhibitory strength in behaviorally relevant frequency regions. Fidelity and inhibitory strength can be lost following auditory nerve injury leading to diminished sensory outcome and increased central noise