Nanoscale switch for vortex polarization mediated by Bloch core formation in magnetic hybrid systems

Abstract

Vortices are fundamental magnetic topological structures characterized by a curling magnetization around a highly stable nanometric core. The control of the polarization of this core and its gyration is key to the utilization of vortices in technological applications. So far polarization control has been achieved in single-material structures using magnetic fields, spin-polarized currents or spin waves. Here we demonstrate local control of the vortex core orientation in hybrid structures where the vortex in an in-plane Permalloy film coexists with out-of-plane maze domains in a Co/Pd multilayer. The vortex core reverses its polarization on crossing a maze domain boundary. This reversal is mediated by a pair of magnetic singularities, known as Bloch points, and leads to the transient formation of a three-dimensional magnetization structure: a Bloch core. The interaction between vortex and domain wall thus acts as a nanoscale switch for the vortex core polarization.

Localized magnetic fields enhance the field sensitivity of the gyrotropic resonance frequency of a magnetic vortex

“…In the case of fields which approximate those generated by magnetic particles of varying radius, the frequency was observed to be maximized for some intermediate particle size which led to an optimized combination of field amplitude and field localization. This may be relevant for vortex-based MNP sensors exploiting changes of the gyrotropic frequency induced by localized MNP fields 58 . We finally note that this work has focused on very low amplitude excitations and highlight the fact that gyrotropic motion outside of the strongest part of the localized field will result in weaker changes to f G (as observed by Min et al 39 for large amplitude oscillations around pinning sites generated by changes in saturation magnetization).…”

Complex spin configurations in hybrid magnetic multilayer structures due to mutual spin imprinting

“…Understanding coupling between hard and soft regions is essential for the development of a wide range of technologies, including multilayer data storage media [14,15], radio-frequency nano-oscillators [16,17] and artificial multiferroics [18][19][20]. Recently, we identified a novel mode of vortex core polarity reversal in Co/Pd-NiFe multilayer systems, in which reversal occurs via the collapse of the core magnetization to a Bloch core with no out-of-plane component [13]. Crucially, this mode requires mutual spin imprinting between the layers [12], resulting in a complex superposition of a Landau state onto a maze domain pattern.…”

“…Interlayer coupling can induce spatial frustration effects [5], domain wall pinning [8] and multi-domain formation [7]. Further complexity occurs if perpendicular anisotropy structures are coupled to systems with in-plane anisotropy [11,12,13]. Understanding coupling between hard and soft regions is essential for the development of a wide range of technologies, including multilayer data storage media [14,15], radio-frequency nano-oscillators [16,17] and artificial multiferroics [18][19][20].…”

Vortex-dynamics-mediated low-field magnetization switching in an exchange-coupled system

“…Those studies focus on the control of magnetic moments in the vortex. Although interplay of the vortex in a magnet and the magnetization in an adjacent exchange-coupled magnet was investigated in a previous paper [15], no one has tried to use magnetic vortex dynamics in a soft magnet as a route to switching the magnetization of a hard magnet. Here, we show H rf -induced vortex dynamics in soft magnetic Py non-locally triggers the magnetization switching of hard magnetic L1 0 -FePt, which can balance competing goals for reducing H sw and maintaining the thermal stability of magnetization in a nanosized magnet.…”