Abstract
The field of magnonics, which utilizes propagating spin waves for nanoscale transmission and processing of information, has been significantly advanced by the advent of the spin–orbit torque. The latter phenomenon allows one to overcome two main drawbacks of magnonic devices—low energy efficiency of the conversion of electrical signals into spin-wave signals and fast spatial decay of spin waves in thin-film waveguiding structures. At first glance, the excitation and amplification of spin waves by spin–orbit torques seem to be straightforward. Recent research indicates, however, that the lack of the mode selectivity in the interaction of spin currents with dynamic magnetic modes and the onset of dynamic nonlinear phenomena represent significant obstacles. Here, we discuss the possible route to overcoming these limitations, based on the suppression of nonlinear spin-wave interactions in magnetic systems with perpendicular magnetic anisotropy. We show that this approach enables efficient excitation of coherent magnetization dynamics and propagating spin waves in extended spatial regions and is expected to enable practical implementation of complete compensation of spin-wave propagation losses.
Highlights
High-frequency spin waves propagating in thin ferromagnetic films have been utilized for the implementation of advanced microwave devices for many decades.[1,2,3,4,5] The unique features of these waves include electronic tunability by the magnetic field, very short wavelengths in the microwave frequency range, as well as controllability of propagation characteristics by the direction of the static magnetic field relative to the direction of wave propagation.[3,4,5] These features made spin waves very attractive for the implementation of a variety of devices for communication technologies, such as microwave filters, phase shifters, delay lines, multiplexers, etc
Even if low conversion losses can be achieved in traditional macroscopic spin-wave devices with millimeter-scale dimensions, miniaturization of magnonic devices down to the submicrometer scale inevitably results in large conversion losses unacceptable for real-world applications
Downscaling of magnonic devices presents a large number of new challenges, which must be addressed before spin-wave technology becomes a competitive alternative to conventional CMOS-based microelectronics
Summary
High-frequency spin waves propagating in thin ferromagnetic films have been utilized for the implementation of advanced microwave devices for many decades.[1,2,3,4,5] The unique features of these waves include electronic tunability by the magnetic field, very short (millimeter to submicrometer) wavelengths in the microwave frequency range, as well as controllability of propagation characteristics by the direction of the static magnetic field relative to the direction of wave propagation.[3,4,5] These features made spin waves very attractive for the implementation of a variety of devices for communication technologies, such as microwave filters, phase shifters, delay lines, multiplexers, etc. In contrast to the conventional spin torques produced by the local current injection through conducting magnetic materials, the spin–orbit torque (SOT) associated with charge to spin conversion in the bulk or at interfaces in material systems with strong spin– orbit interaction[33–36] provides the ability to control magnetic damping in spatially extended regions of both conducting and insulating magnetic materials.[37–39] This may enable decay-free propagation of spin waves or even their true amplification in magnetic nanostructures. We discuss a recently proposed approach that allows efficient control of nonlinear damping by utilizing reduction of ellipticity of magnetization precession in magnetic films, where the dipolar anisotropy is compensated by the interfacial perpendicular magnetic anisotropy (PMA) This approach has been recently shown to enable SOT-driven excitation of coherent magnetization auto-oscillations in spatially extended systems based on conductive[64] and insulating[65] magnetic materials. We expect that this approach can enable the implementation of decay-free propagation of spin waves, resolving, in this way, the main issues limiting the progress in nano-magnonics
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