Chiral excitations of magnetic droplet solitons driven by their own inertia

Abstract

The inertial effects of magnetic solitons play a crucial rule in their dynamics and stability. Yet governing their inertial effects is a challenge for their use in real devices. Here, we show how to control the inertial effects of magnetic droplet solitons. Magnetic droplets are strongly nonlinear and localized autosolitons than can form in current-driven nanocontacts. Droplets can be considered as dynamical particles with an effective mass. We show that the dynamical droplet bears a second excitation under its own inertia. These excitations comprise a chiral profile, and appear when the droplet resists the force induced by the Oersted field of the current injected into the nanocontact. We show how to control these chiral modes using the current and the field.

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

“…4b). This is in accordance with our expectations since such modes for a localized droplet feature a chiral profile due to the interplay between the STT and the induced force [48]. It is interesting to note that the shape deformations of the droplet during propagation lead to a small modulation of its trajectory (toward the y-axis) along the propagation direction.…”

“…3b. In addition to the main droplet frequency, sidebands appear evidencing the droplet's inertial effects, i.e., its tendency to resist the exerted torque due to the broken symmetry [48]. Moreover, it is evident that a higher ‫ܭ‬ ௨ଵ leads to a larger linewidth in the frequency spectra of the moving droplet.…”

Freezing and thawing magnetic droplet solitons

“…Magnetic droplets are intrinsically dynamic, non-topological, magnetodynamical solitons [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] , which can be nucleated and sustained both in spin torque nano-oscillators (STNOs) 3,6,8,12,14 and spin Hall nano-oscillators (SHNOs) 16 , provided the magnetodynamically active layer has sufficient perpendicular magnetic anisotropy (PMA). Magnetic droplets are characterized by a reversed core separated from the surrounding magnetization via a perimeter of precessing spins (See Fig.…”

“…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] .…”