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Magnetic droplets are self-localized spin wave solitons that can be excited in spin valves with perpendicular magnetic anisotropy by using spin-transfer torque generated by a dc current through a nano-contact. Using micromagnetic simulations, we demonstrate that the droplet soliton mode could be switched to a localized spiral precession mode due to the resistance effect of current-induced Oersted fields whose rotation direction is opposite to the precession direction of droplet. This spiral mode can switch back to the droplet mode by increasing current. With an assistance of electric field, both the localized droplet and spiral modes can develop to the radially propagating spin waves. The frequencies of all these localized spiral and droplet as well as the propagating spin wave modes show linear increase relationship with a magnetic field applied in out-of-plane direction. These results are of fundamental interest in understanding the rich dynamics of magnetic excitation properties, which will be helpful for the droplet-based spintronic devices.

The magnetic skyrmions have received a lot of attention because they have potential applications in spin torque nano-oscillators. In this paper, we numerically and analytically study the dynamics of edge skyrmions in circular nano-pillar oscillators with perpendicular magnetic anisotropy (PMA) free layer and spin polarizer. Numerical simulations demonstrate that a steady edge skyrmion oscillation mode with GHz frequency can be driven by spin currents and magnetic fields. The oscillation frequencies in circular nano-pillars with different radius are analytically derived, which agrees well with the numerical results. In addition, the steady oscillations of edge skyrmions are also observed in elliptical nano-pillars, in which the oscillation frequencies strongly depend on the eccentricity and perimeter of the elliptical nanopillar. It is found that the oscillation frequency of this edge skyrmion can range from 1 GHz to 6.7 GHz. The line width is about 55 MHz.

The effective manipulation of skyrmion motion by magnetic field gradients introduces the technological possibility with skyrmion as information carriers for spintronic applications. Recent studies indicate that the skyrmion Hall effect can be suppressed in a synthetic antiferromagnetic (SAF) multilayer structure driven by a spin polarized current. In this paper, an analytical model based on Thiele equation is developed to describe the properties of a skyrmion pair in a SAF structure driven by a magnetic field gradient. Combining the analytical solutions with the micromagnetic simulation results, we demonstrate the essential dynamic features of the skyrmion pair as a function of AF coupling and magnetic field gradients, revealing that the skyrmion pair motion could be suppressed by increasing the interlayer antiferromagnetic coupling.