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Register a new userEnhancement of the spin pumping efficiency by spin-wave mode selection
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The spin pumping efficiency of lateral standing spin wave modes in a rectangular YIG/Pt sample has been investigated by means of the inverse spin-Hall effect (ISHE). The standing spin waves drive spin pumping, the generation of spin currents from magnetization precession, into the Pt layer which is converted into a detectable voltage due to the ISHE. We discovered that the spin pumping efficiency is significantly higher for lateral standing surface spin waves rather than for volume spin wave modes. The results suggest that the use of higher-mode surface spin waves allows for the fabrication of an efficient spin-current injector.
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We experimentally show that exchange magnons can be detected using a combination of spin pumping and inverse spin-Hall effect (iSHE) proving its wavelength integrating capability down to the sub-micrometer scale. The magnons were injected in a ferrimagnetic yttrium iron garnet film by parametric pumping and the iSHE-induced voltage was detected in an attached Pt layer. The role of the density, wavelength, and spatial localization of the magnons for the spin pumping efficiency is revealed. This study opens the field of the magnon-based information processing to magnons with nano-scale wavelengths.
Surface acoustic waves (SAWs) in the GHz frequency range can inject spin currents dynamically into adjacent nonmagnetic layers via spin pumping effect associated with ferromagnetic resonance. Here, we demonstrate an enhancement of acoustic ferromagnetic resonance and spin current generation by a pair of SAW reflector gratings, which form an acoustic analogue of the distributed Bragg reflector cavity. In the experiment, we confirmed 2.04 $pm$ 0.02 times larger SAW power absorption in a device with cavity than in case of no acoustic cavity. We confirmed up to 2.96 $pm$ 0.02 times larger spin current generation by measuring electric voltages generated by the inverse Edelstein effect (IEE) at the interface between Cu and Bi$_2$O$_3$. The results suggest that acoustic cavities would be useful to enhance the conversion efficiency in SAW driven coupled magnon-phonon dynamics.
We have demonstrated spin pumping from a paramagnetic state of an insulator La2NiMnO6 into a Pt film. Single-crystalline films of La2NiMnO6 which exhibit a ferromagnetic order at TC ~ 270 K were grown by pulsed laser deposition. The inverse spin Hall voltage induced by spin-current injection has been observed in the Pt layer not only in the ferromagnetic phase of La2NiMnO6 but also in a wide temperature range above TC. The efficient spin pumping in the paramagnetic phase is ascribable to ferromagnetic correlation, not to ferromagnetic order.
To understand and optimize optical spin initialization in room temperature CdSe nanocrystal quantum dots (NCQDs) we studied the dependence of the time-resolved Faraday rotation signal on pump energy $E_p$ in a series of NCQD samples with different sizes. In larger NCQDs, we observe two peaks in the spin signal vs. $E_p$, whereas in smaller NQCDs, only a single peak is observed before the signal falls to a low, broad plateau at higher energies. We calculate the spin-dependent oscillator strengths of optical transitions using a simple effective mass model to understand these results. The observed $E_p$ dependence of the spin pumping efficiency (SPE) arises from the competition between the heavy hole (hh), light hole (lh) and split-off (so) band contributions to transitions to the conduction band. The two latter contributions lead to an electron spin polarization in the opposite direction from the former. At lower $E_p$ the transitions are dominated by the hh band, giving rise to the low energy peaks. At higher $E_p$, the increasing contributions from the lh and so bands lead to a reduction in SPE. The different number of peaks in larger and smaller NCQDs is attributed to size-dependence of the ordering of the valence band states.
The spin-wave dynamics of the ferromagnetic nanoarrays termed artificial spin ice (ASI) are known to vary depending on their magnetic microstate. However, little work has been done to characterise this relationship. Recent advances in control over the magnetic configuration of ASI bring designs harnessing the interplay between spin-wave eigenmodes and the microstate within reach, offering diverse applications including reconfigurable magnonic crystals, microwave filters and microstate read-out probes. These designs hinge on a strong understanding of the underlying spin wave-microstate correspondence. Here, we analyse the effects of the magnetic microstate on spin-wave spectra of honeycomb ASI systems via micromagnetic simulation. We find the spin-wave spectrum to be highly-tunable via the microstate to an enhanced degree relative to existing magnonic crystals, with mode shifting and (de)activation realised by reversing individual nanoislands. Symmetries of ASI systems and the chirality of magnetic defects are found to play important roles in determining the high-frequency response.
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