Wireless magneto-ionics: voltage control of magnetism by bipolar electrochemistry

Abstract

Modulation of magnetic properties through voltage-driven ion motion and redox processes, i.e., magneto-ionics, is a unique approach to control magnetism with electric field for low-power memory and spintronic applications. So far, magneto-ionics has been achieved through direct electrical connections to the actuated material. Here we evidence that an alternative way to reach such control exists in a wireless manner. Induced polarization in the conducting material immersed in the electrolyte, without direct wire contact, promotes wireless bipolar electrochemistry, an alternative pathway to achieve voltage-driven control of magnetism based on the same electrochemical processes involved in direct-contact magneto-ionics. A significant tunability of magnetization is accomplished for cobalt nitride thin films, including transitions between paramagnetic and ferromagnetic states. Such effects can be either volatile or non-volatile depending on the electrochemical cell configuration. These results represent a fundamental breakthrough that may inspire future device designs for applications in bioelectronics, catalysis, neuromorphic computing, or wireless communications.

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“…Thus, in the case of recent studies on CoN reduction (Fig. 14 and 15), along with magnetic changes, 105 a vertical bipolar electrode parallel to the external electrodes, removes the gradient across the surface, while keeping it in the direction of the field. Thus, it results in a permanent magnetic change in the vertical arrangement and a gradient that evolves with time in the horizontal arrangement.…”

“…The bipolar charging effect depends on the size of the metal immersed in a first simple approach, as mentioned before. It can occur at small scales including nanoparticles, as it has been found in very thin layers (50 nm of cobalt nitride, CoN, on Au), 105 in Janus particles, Au nanoparticles 106,107 and others. 103 Thus, previous work reported using coatings of gold nanoparticles where neurite outgrowth was observed under EF conditions may now be considered using in a new perspective.…”

“…103 Thus, previous work reported using coatings of gold nanoparticles where neurite outgrowth was observed under EF conditions may now be considered using in a new perspective. 105 Although no data for possible electronic percolation had been extracted it can be assumed that in such work the bipolar effect was also acting though polarization of the gold nanoparticles.…”

“…Analogous gradients have been observed in other physical properties recently. 105 The case of bipolar CoN reduction yielding Co at the induced cathode is a significant example, since ferromagnetism is generated in a gradient, along with a gradient formation of Co. Time evolution of the magnetic signal is also observed after the electric field is turned off, and the material allowed to discharge 105 for specific configurations. This suggests future applications based on resistance or magnetization changes in biological systems as long as biocompatible materials are used.…”

“…The more recent studies on cobalt nitride, CoN, bipolar reduction evidence an analogous behaviour. If discharge is allowed, the process becomes reversible 105 and switching the device could be implemented. Simultaneously, microgradients are created that impede a full range order and crystallinity, and that are possibly tolerated better in a polymeric structure like that of PEDOT, that may change conformation with oxidation states.…”