Voltage‐Controlled Deblocking of Magnetization Reversal in Thin Films by Tunable Domain Wall Interactions and Pinning Sites

Abstract

so far, mainly originates from the elec tric currents utilized to control the mag netic properties. A promising alternative for increasing the energy efficiency of magnetic devices is to control the mag netism by electric fields instead of electric currents. This possibility has triggered intense research into magnetoelectric materials, but much of this is restricted to low temperature and high voltage opera tion and/or complex layer synthesis. [1] More recently, magnetoelectric appro aches involving the voltagegating of mag netic nanostructures via a dielectric oxide or an electrolyte were examined. [1-3] In these approaches, ferro and ferrimagnetic metals or oxides exhibiting Curie tem peratures above room temperature can be used and often only few volts are required during gating. The modulation of mag netic properties in voltagegated magnetic nanostructures is based on either voltage induced capacitive charging or electro chemical (magnetoionic) processes. [2-4] Voltageinduced capacitive charging of a ferromagnetic metal interface causes volatile changes in the sur face electronic band structure that affect the intrinsic magnetic properties in just a few atomic layers. [5-10] In contrast, magneto ionic mechanisms involve voltageinduced ion migration and electrochemical reactions, [2,3,11-13] and can therefore induce very large and nonvolatile magnetic property changes. [12,14-18] As a High energy efficiency of magnetic devices is crucial for applications such as data storage, computation, and actuation. Redox-based (magneto-ionic) voltage control of magnetism is a promising room-temperature pathway to improve energy efficiency. However, for ferromagnetic metals, the magnetoionic effects studied so far require ultrathin films with tunable perpendicular magnetic anisotropy or nanoporous structures for appreciable effects. This paper reports a fully reversible, low voltage-induced collapse of coercivity and remanence by redox reactions in iron oxide/iron films with uniaxial in-plane anisotropy. In the initial iron oxide/iron films, Néel wall interactions stabilize a blocked state with high coercivity. During the voltage-triggered reduction of the iron oxide layer, in situ Kerr microscopy reveals inverse changes of coercivity and anisotropy, and a coarsening of the magnetic microstructure. These results confirm a magneto-ionic deblocking mechanism, which relies on changes of the Néel wall interactions, and of the microstructural domainwall-pinning sites. With this approach, voltage-controlled 180° magnetization switching with high energy-efficiency is achieved. It opens up possibilities for developing magnetic devices programmable by ultralow power and for the reversible tuning of defect-controlled materials in general.

Dependence of magnetic domain patterns on plasma-induced differential oxidation of CoPd thin films

“…This demonstrates the potential of plasma-triggered oxidation for enhancing the variety of magnetic patterning with variable oxidation breadths and depths. If further incorporated with precisely controllable or even reversible oxidation techniques such as a gating structure that enables voltage-induced oxidation and reduction [24,45], oxidationinduced domain patterning can be a powerful technique for future data-storage and spintronic devices.…”

Magneto-ionic suppression of magnetic vortices

“…This is very appealing because the use of voltage (instead of electrical currents) minimizes Joule heating effects and it can thus be considered as a highly energy-efficient actuation protocol. [23] Voltage has been shown to induce changes in the coercivity, [24] net magnetization, [25] remanence, [26] exchange bias, [27] Curie temperature [28] and magnetoresistance, [29,30] of the investigated materials. Several ME mechanisms have been identified: intrinsic ME coupling in singlephase multiferroics, electric surface charging in ultra-thin films, magneto-ionics (voltagedriven ion migration), and strain-mediated effects in piezoelectric/magnetostrictive composites.…”

Voltage control of magnetism with magneto-ionic approaches: Beyond voltage-driven oxygen ion migration

“…(c) Sketch of some magnetic parameters which may be turned in a magneto-ionic system, including saturation magnetization, coercive field, exchange bias, magnetic anisotropy, and Curie Temperature. 82,[90][91][92][93][94][95][96][97] stoichiometry, oxidation state, crystalline structure, as well as large and cyclable changes in magnetic properties [Fig. 1(c)].…”

“…1(c)]. 82,[90][91][92][93][94][95][96][97] Magnetoionic materials also offer several potential advantages for practical applications: They potentially require lower energy to actuate (as low %10 aJ/bit, 98,99 much lower than traditional current-using methods, %10 fJ/bit 100 ), no voltage to maintain a set state (nonvolatile) and offer the possibility of functional plasticity (i.e., the ability to undergo nonvolatile changes in its structure and properties in response to an external stimulus), making magneto-ionic materials intriguing candidates to be deployed in neuromorphic or stochastic computing, magnetic random access memory, domain-wall logic, and lab-on-a-chip devices. [101][102][103] Indeed, magneto-ionics has already been identified for potential use in several applications.…”

“…Oxide/ metal heterostructures in thin films and islands have been explored using Fe/FeO x 96,146 and Co/CoO x structures, allowing the reversible removal and insertion of oxygen to toggle magnetic states. In particular, on-off switching of magnetism has been observed in ironbased hybrid transition metal oxide/metal, 90,140,147 transition metal oxide [148][149][150][151] films, and porous structures. Along this vein, we discuss our recent work on the structural-ion approach, where the target material possesses the migrating anions in the as-deposited state, in single layer oxide and nitride films, and so providing a crystal structure with more local vacancies and larger ionic pathways, facilitating ion movement in and out of the target material with reduced structural distortion.…”