Freezing and thawing magnetic droplet solitons

We use all-perpendicular nanocontact spin-torque oscillators to study the low-field behavior of magnetic droplets. These dissipative solitons are inherently dynamic and are characterized by a core of reversed spins surrounded by a precessing perimeter [1, 2, 3, 4]. The precession frequency lies between the ferromagnetic and Zeeman resonances, but the droplet is also prone to drift which gives additional dynamics [5, 6]. Electrical measurements reveal that the droplet transforms, freezes, into a static bubble at low fields. Once formed, the bubble is stable without a sustaining current. Furthermore, the droplet-to-bubble transition is fully reversible and the bubble can thaw back to a droplet at sufficient high field and current. The findings are corroborated by X-ray microscopy, which images the magnetic states during the freezing. Experimental data together with simulations identify pinning as the main mechanism behind the bubble stability.

 

[1] Hoefer et al., PRB 82, 054432 (2010)

[2] Mohseni et al., Science 339, 1295 (2013)

[3] Chung et al., J. Appl. Phys 115, 172612 (2014)

[4] Chung et al., PRL 120, 217204 (2018)

[5] Xiao et al., PRB 95, 024106 (2017)

[6] Chung et al, Nat. Com. 7, 11209 (2016)