Magneto-ionic suppression of magnetic vortices

Abstract

Magneto-ionics refers to the non-volatile control of the magnetic properties of materials by voltage-driven ion migration. This phenomenon constitutes one of the most important magnetoelectric mechanisms and, so far, it has been employed to modify the magnetic easy axis of thin films, their coercivity or their net magnetization. Herein, a novel magneto-ionic effect is demonstrated: the transition from vortex to coherent rotation states, caused by voltage-induced ion motion, in arrays of patterned nanopillars. Electrolyte-gated Co/GdO x bilayered nanopillars are chosen as a model system. Electron microscopy observations reveal that, upon voltage application, oxygen ions diffuse from GdO x to Co, resulting in the development of paramagnetic oxide phases (CoO x ) along sporadic diffusion channels. This breaks up the initial magnetization configuration of the ferromagnetic pillars (i.e., vortex states) and leads to the formation of small ferromagnetic nanoclusters, embedded in the CoO x matrix, which behave as single-domain nanoparticles. As a result, a decrease of the net magnetic moment is observed, together with a drastic change in the shape of the hysteresis loop. Micromagnetic simulations are used to interpret these findings. These results pave the way towards a new potential application of magnetoelectricity: the magneto-ionic control of magnetic vortex states.

Highly cyclable voltage control of magnetism in cobalt ferrite nanopillars for memory and neuromorphic applications

“…Remarkably, studies on magneto-ionic effects in arrays of patterned or self-assembled dots or islands are rather scarce. 32,[34][35][36] If magneto-ionics could be demonstrated to be applicable to dense, high surface area nanopillar arrays, the phenomenon could be used in patterned magnetic recording media or as an array of interconnected synapses. [37][38][39] The non-volatility and energy efficiency of the magneto-ionic effect in the nanopillar arrays could be a key enabler for next-generation data storage, 1,22,28 provided durability, cyclability, and magnitude of the magnetic response were satisfied also.…”