Perspectives of using spin waves for computing and signal processing

https://hal-cea.archives-ouvertes.fr/cea-01507592/document

Magnetization oscillations and waves driven by pure spin currents

Spin-wave propagation in microfabricated 20 nm thick, 25 μm wide Yttrium Iron Garnet (YIG) waveguides is studied using propagating spin-wave spectroscopy (PSWS) and phase resolved micro-focused Brillouin Light Scattering (μ-BLS) spectroscopy We demonstrate that spin-wave propagation in 50 parallel waveguides is robust against microfabrication induced imperfections and extract spin-wave propagation parameters for the Damon-Eshbach configuration in a wide range of excitation frequencies As expected from its low damping, YIG allows for the propagation of spin waves over long distances; the attenuation lengths is 25 μm at μ 0 H = 45 mT Moreover, direct mapping of spin waves by μ-BLS allows us to reconstruct the spin-wave dispersion relation and to confirm the multi-mode propagation in the waveguides, glimpsed by propagating spin-wave spectroscopy

Spin-wave propagation in ultra-thin YIG based waveguides

We study experimentally with submicrometer spatial resolution the propagation of spin waves in microscopic waveguides based on the nanometer-thick yttrium iron garnet and Pt layers. We demonstrate that by using the spin-orbit torque, the propagation length of the spin waves in such systems can be increased by nearly a factor of 10, which corresponds to the increase in the spin-wave intensity at the output of a 10 μm long transmission line by three orders of magnitude. We also show that, in the regime, where the magnetic damping is completely compensated by the spin-orbit torque, the spin-wave amplification is suppressed by the nonlinear scattering of the coherent spin waves from current-induced excitations.

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High-efficiency control of spin-wave propagation in ultra-thin yttrium iron garnet by the spin-orbit torque

Spin insulatronics covers efforts to generate, detect, control, and utilize high-fidelity pure spin currents and excitations inside magnetic insulators. Ultimately, the new findings may open doors for pure spin-based information and communication technologies. The aim is to replace moving charges with dynamical entities that utilize low-dissipation coherent and incoherent spin excitations in antiferromagnetic and ferromagnetic insulators. The ambition is that the new pure spin-based system will suffer reduced energy losses and operate at high frequencies. In magnetic insulators, there are no mobile charge carriers that can dissipate energy. Integration with conventional electronics is possible via interface exchange interactions and spin-orbit couplings. In this way, the free electrons in the metals couple to the localized spins in the magnetic insulators. In turn, these links facilitate spin-transfer torques and spin-orbit torques across metal-insulator interfaces and the associated phenomena of spin-pumping and charge-pumping. The interface couplings also connect the electron motion inside the metals with the spin fluctuations inside the magnetic insulators. These features imply that the system can enable unprecedented control of correlations resulting from the electron-magnon interactions. We review recent developments to realize electric and thermal generation, manipulation, detection, and control of pure spin information in insulators.

Spin Insulatronics

We have investigated recrystallization of amorphous Yttrium Iron Garnet (YIG) by annealing in oxygen atmosphere. Our findings show that well below the melting temperature the material transforms into a fully epitaxial layer with exceptional quality, both structural and magnetic. In ferromagnetic resonance (FMR) ultra low damping and extremely narrow linewidth can be observed. For a 56 nm thick layer a damping constant of α = (6.15 ± 1.50) · 10−5 is found and the linewidth at 9.6 GHz is as small as 1.30 ± 0.05 Oe which are the lowest values for PLD grown thin films reported so far. Even for a 20 nm thick layer a damping constant of α = (7.35 ± 1.40) · 10−5 is found which is the lowest value for ultrathin films published so far. The FMR linewidth in this case is 3.49 ± 0.10 Oe at 9.6 GHz. Our results not only present a method of depositing thin film YIG of unprecedented quality but also open up new options for the fabrication of thin film complex oxides or even other crystalline materials.

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Yttrium Iron Garnet Thin Films with Very Low Damping Obtained by Recrystallization of Amorphous Material.

Spin pumping describes the flow of a spin current from a ferromagnet into an adjacent conductor due to spin precession or thermal gradients in the ferromagnet. To measure its magnitude, often the damping of the ferromagnet in ferromagnetic resonance is investigated, which increases when spin pumping takes place. However, in the experiments shown here, it is shown that electromagnetic interactions between the ferromagnet and the conducting nonmagnet with the exciting magnetic radio-frequency field can also cause additional damping. This so-called radiation damping can mimic spin pumping where none exists or at least considerably falsify the results obtained from the standard evaluation of the experiment.

Radiation damping in ferromagnetic resonance induced by a conducting spin sink

The authors provide experimental results that show the onset of the Nernst effect, thermovoltages and an inverse spin-Hall effect in the polymer PEDOT:PSS. Specifically, the observed inverse spin-Hall effect appears to be smaller than other measurements, but in better agreement with theoretical calculations.

Mohammad M. Qaid

Papers

Yttrium Iron Garnet Thin Films with Very Low Damping Obtained by Recrystallization of Amorphous Material.

Radiation damping in ferromagnetic resonance induced by a conducting spin sink

Quantifying the inverse spin-Hall effect in highly doped PEDOT:PSS