Propagating Magnetic Droplet Solitons as Moveable Nanoscale Spin-Wave Sources with Tunable Direction of Emission

Abstract

Magnetic droplets are strongly nonlinear and localized spin-wave solitons that can be formed in current-driven nanocontacts. Here, we propose a simple way to launch droplets in an inhomogeneous nanoscopic waveguide. We use the drift motion of a droplet and show that in a system with broken translational symmetry, the droplet acquires a linear momentum and propagates. We find that the droplet velocity can be tuned via the strength of the break in symmetry and the size of the nanocontact. In addition, we demonstrate that the launched droplet can propagate up to several micrometers in a realistic system with reasonable damping. Finally, we demonstrate how an annihilating droplet delivers its momentum to a highly nonreciprocal spin-wave burst with a tunable wave vector with nanometer wavelengths. Such a propagating droplet can be used as a moveable spin-wave source in nanoscale magnonic networks. The presented method enables full control of the spin-wave emission direction, which can largely extend the freedom to design integrated magnonic circuits with a single spin-wave source.

Tuning the dynamics of magnetic droplet solitons using dipolar interactions

“…in a nanowire or if the NC is placed near the edges of the setup. However, the latter configuration can lead to drift instabilities and droplet propagation [25,30].…”

“…This essentially means that droplets are dissipative solitons since they only sustain if the damping of the system is compensated by the STT (gain). The strong nonlinearity of the droplets given by their very large angle of precession leads to various intriguing nonlinear and instability dynamics [23][24][25][26][27][28][29][30][31]. This also leads to a strong output power compared to similar devices, suggesting the benefits of droplet-STNOs in microwave data processing devices, magnonic and spintronic applications.…”

“…However, conducting analytical calculations for this aim in such a strongly nonlinear and nonuniform magnetodynamics is a rather tedious and challenging task that encourages the use of numerical approaches to tackle this issue. Indeed, numerical simulations based on the micromagnetic frameworks is now a reliable and well established method to study magnetodynamics in nanostructures, including various nonlinear dynamics of droplets [26,29,30,[34][35][36][37]. Needles to mention that the studies based on such methods turned out with excellent agreements to the experimental observations and theoretical analysis.…”

Freezing and thawing magnetic droplet solitons

“…After the first experimental demonstration of magnetic droplets, reported in STNOs with a PMA Co/Ni free layer and a Co fixed layer 3 , interest in magnetic droplets continues to increase due to its interesting characteristics, such as a highly nonlinear dynamics 2,11,19 , large power emission 3,10,20,21 , and possible applications in microwave-assisted magnetic recording (MAMR) 22,23 and neuromorphic chips as nonlinear oscillators [24][25][26] . Several theoretical 5,11,15,19,[27][28][29][30][31][32][33] and experimental 6-10, 12, 16, 21, 34-38 studies on magnetic droplets have since been presented. and they identify a possible zero-frequency droplet with a topologically trivial magnetic bubble [39][40][41][42][43] .…”

Freezing and thawing magnetic droplet solitons

“…After the first experimental demonstration of magnetic droplets, reported in STNOs with a PMA Co/Ni free layer and a Co fixed layer 3 , interest in magnetic droplets continues to increase due to its interesting characteristics, such as a highly nonlinear dynamics 2,11,19 , large power emission 3,10,20,21 , and possible applications in microwave-assisted magnetic recording (MAMR) 22,23 and neuromorphic chips as nonlinear oscillators [24][25][26] . Several theoretical 5,11,15,19,[27][28][29][30][31][32][33] and experimental 6-10, 12, 16, 21, 34-38 studies on magnetic droplets have since been presented. and they identify a possible zero-frequency droplet with a topologically trivial magnetic bubble [39][40][41][42][43] .…”