Electrolyte-gated magnetoelectric actuation: Phenomenology, materials, mechanisms, and prospective applications

Abstract

Manipulation of the magnetic behavior of materials with voltage (i.e., magnetoelectric actuation) has become a topic of intense research during the last years. Apart from its obvious interest from a basic science standpoint, control and eventual switching of the magnetization without applying any external magnetic field (or spin polarized current) has the potential to drastically reduce the power consumption of magnetic devices due to the lack (or minimization) of Joule heating dissipation effects. Herein, an overview of the state-of-the-art of electrolyte-gated magnetoelectric actuation (where an electric field is applied using an electrolyte, either liquid or solid) is provided. The different types of mechanisms responsible for voltage-driven magnetic actuation (surface charging, ionic migration, also termed “magneto-ionics,” reduction/oxidation reactions, and ferroelectric/ferromagnetic coupling) are summarized. The various effects (changes in coercivity, anisotropy easy axis, exchange bias field, saturation magnetization, Curie temperature, etc.) observed in the different types of materials investigated so far (mainly metallic thin films and semiconductors, porous alloys, and nanocomposite structures) are described. The potential applications of electrolyte-gated magnetoelectric actuation in devices as well as the current challenges in the field are also reviewed with the aim of providing the basic ingredients for further prospects and technological advancements in this area.

Reversible Tuning of Magnetization in a Ferromagnetic Ruddlesden–Popper‐Type Manganite by Electrochemical Fluoride‐Ion Intercalation

“…This shows that by choosing a low cut‐off voltage in the charging process, the absolute magnetic moments could be increased, but the relative change in magnetization due to the fluoride (de)intercalation remained the same. Due to the fact that the cells can be operated at very low potentials (Δ V = 0.75 or 0.9 V for V C, charge = 0.45 or 0.6 V, respectively), the cells shown here possess among the highest magnetoelectric couplings for tunable magnetic systems observed so far . Further, it is interesting to note that the electrochemically treated samples possess slightly higher coercivities than the La 1.3 Sr 1.7 Mn 2 O 7 base sample, though the coercivity remains stable within errors comparing the different charged and uncharged samples, and appears to be independent on the cut‐off conditions (Figure S13, Supporting Information).…”

“…We show that a 67% reversible change in magnetization is possible in this material by fluoride ion (de)intercalation, comparable to the best Li‐ion intercalation systems. What is more, our operating potentials of <1 V are lower than those typically required for the Li‐ion intercalation (≈2 V), leading to higher magnetoelectric efficiency α.…”

“…Magnetoelectric control, that is, using an electric field to control material's magnetic properties (magnetic state, moment, ordering temperature, etc.) is of great fundamental interest, but also enables various applications, such as spin‐based electronics, magnetic data storage, micromagnetic actuation, and sensors . Depending on the application, there can be different requirements on the magnetoelectric system, such as high magnetic on/off ratio, long‐term stability and reversibility, speed of operation, or a particular operating voltage range or temperature.…”

“…Depending on the application, there can be different requirements on the magnetoelectric system, such as high magnetic on/off ratio, long‐term stability and reversibility, speed of operation, or a particular operating voltage range or temperature. While various magnetoelectric systems already exist, new approaches to control magnetic material properties are still sought after in order to improve on the different requirements for different applications. There, a special focus lies in materials which possess a high magnetoelectric voltage coefficient α = Δ M /(Δ V × M ) (the change of relative magnetization, Δ M / M , per applied voltage, Δ V ), as it provides for high energy efficiency in applications …”

Magneto‐Ionic Switching of Superparamagnetism

“…One can distinguish three fundamentally different processes at the electrode–electrolyte interface, which can be exploited for the electrochemical control of magnetism: I) capacitive or pseudo‐capacitive double‐layer charging, II) redox surface reactions, or III) bulk intercalation triggered by chemical reactions (magneto‐ionic effect) . As high surface‐to‐volume ratios are beneficial for all three tuning approaches, recent studies have mainly focused on ultra‐thin films and nanoporous materials …”