Interplay of Spin-Torque and Nonlinearity: Disentangling and Controlling Magnon Processes in Nanomagnets*

Nanoscale magnets are the building blocks of many spintronics technologies. However, various aspects of spin dynamics in the nanoscale geometrical confinement have remained elusive. For instance, untangling damping contributions and engineering spin-torque response in nanomagnets is often a challenging task.

Using magnetic tunnel junctions as a sample platform, we investigate the discrete magnon spectrum of individual zero-dimensional magnets and identify the inherent inter-magnon processes. While manipulation of magnetization by spin-torque is a key functionality of today’s spintronics, we find that resonant magnon processes redefine and invert a nanomagnet's response to spin-torque [1]. We discuss the mechanisms of this counter-intuitive interplay of nonlinearity and spin-torque, which has far-reaching implications for the performance of magnetic memory and oscillators.

Controlling magnon processes and thus forging the nonlinearity of a nanomagnet would add decisive functionality to existing and emerging technologies, in particular to magnetic neuromorphic systems where tunability of the nonlinear response is instrumental. We develop an approach for engineering magnon interaction by means of symmetry-breaking fields with nanoscale nonuniformity [2]. In a proof-of-concept, we employ a nanoscale synthetic antiferromagnet as a switchable source of such fields and achieve tunability of magnon coupling by at least one order of magnitude. The results open up avenues for controlling magnon processes by external stimuli at nanoscale and show prospects for spin-torque applications and quantum information technologies.

[1] Giant nonlinear damping in nanoscale ferromagnets, I. Barsukov et al., Sci. Adv. 5, eaav6943 (2019)

http://dx.doi.org/10.1126/sciadv.aav6943

[2] Controlling magnon interaction by a nanoscale switch, A. Etesamirad et al., ACS Appl. Mater. Interfaces 13, 20288 (2021)

https://doi.org/10.1021/acsami.1c01562