Generation and annihilation time of magnetic droplet solitons

Jinting Hang,Ferran Macià,Nahuel Statuto,Christian Hahn,Andrew D Kent

doi:10.1038/s41598-018-25134-z

Abstract

Magnetic droplet solitons were first predicted to occur in materials with uniaxial magnetic anisotropy due to a long-range attractive interaction between elementary magnetic excitations, magnons. A non-equilibrium magnon population provided by a spin-polarized current in nanocontacts enables their creation and there is now clear experimental evidence for their formation, including direct images obtained with scanning x-ray transmission microscopy. Interest in magnetic droplets is associated with their unique magnetic dynamics that can lead to new types of high frequency nanometer scale oscillators of interest for information processing, including in neuromorphic computing. However, there are no direct measurements of the time required to nucleate droplet solitons or their lifetime–experiments to date only probe their steady-state characteristics, their response to dc spin-currents. Here we determine the timescales for droplet annihilation and generation using current pulses. Annihilation occurs in a few nanoseconds while generation can take several nanoseconds to a microsecond depending on the pulse amplitude. Micromagnetic simulations show that there is an incubation time for droplet generation that depends sensitively on the initial magnetic state of the nanocontact. An understanding of these processes is essential to utilizing the unique characteristics of magnetic droplet solitons oscillators, including their high frequency, tunable and hysteretic response.

Highlights

Magnetic droplet solitons were first predicted to occur in materials with uniaxial magnetic anisotropy due to a long-range attractive interaction between elementary magnetic excitations, magnons
There have been a number of proposed applications of magnetic droplet solitons that rely on their unique magnetic dynamics[11]
Far experiments only probe the steady-state characteristics of droplet solitons, i.e. their properties when the current has been on or off for long periods compared to the time scale of their intrinsic dynamics

Summary

OPEN Generation and annihilation time of magnetic droplet solitons

Jinting Hang[1], Christian Hahn[1], Nahuel Statuto[2,3], Ferran Macià 2,3 & Andrew D. We start in a non-droplet state, again in the hysteretic region Ic1 < I < Ic2 (indicated by the dashed line in Fig. 1d), and apply a positive polarity current pulse to increase the current above Ic1. We proceed to study the times needed to generate the droplet by initializing the nanocontact in the non-droplet state and applying positive current pulses. (Data on a 150 nm diameter nanocontact is shown in Supplementary Section III) These results show that the time needed to enter the droplet state can be longer than for exiting it; for the same current pulse amplitude it can take orders of magnitude longer to create the droplet than to annihilate it. It will be interesting to study dynamical skyrmions[13,19], which are expected to be longer lived excitations, as well as to examine the effect of temperature on the stability and formation of droplet solitons

Methods

Author Contributions

Findings

Additional Information