Magnetoelectric Charge Trap Memory

Abstract

It is demonstrated that a charge-trapping layer placed in proximity to a ferromagnetic metal enables efficient electrical and optical control of the metal's magnetic properties. Retention of charge trapped inside the chargetrapping layer provides nonvolatility to the magnetoelectric effect and enhances its efficiency by an order of magnitude. As such, an engineered charge-trapping layer can be used to realize the magnetoelectric equivalent to today's pervasive charge trap flash memory technology. Moreover, by supplying trapped charges optically instead of electrically, a focused laser beam can be used to imprint the magnetic state into a continuous metal film. KEYWORDS: Magnetoelectric effect, electric field control of magnetic properties, charge trap flash memory, magneto-optical writing, magnetic anisotropy E lectric field control of the magnetic state of a material could enable new low-power logic devices and nonvolatile memory cells.1−17 Magneto-electric coupling has typically been achieved using complex materials such as multiferroic oxides, 5 dilute magnetic semiconductors, 1,2 or strain-coupled magnetostrictive/piezoelectric composites.3 Only recently, direct electrical control of magnetic anisotropy 4,6,7,9−12 and Curie temperature 8 has been demonstrated in transition metal ferromagnets at room temperature. These effects open the door to electrically gated spintronic devices based on materials amenable to integration with conventional semiconductor electronics.Although magnetoelectric effects are precluded from bulk ferromagnetic metals due to the very short screening length, in films thinner than a few nanometers, spin-dependent charge screening and band level shifting can lead to pronounced electric field-driven changes to magnetic properties. 14−17Unfortunately, magnetoelectric effects in metals require a relatively strong electric field and are inherently volatile. In this work, we show that a charge-trapping layer integrated into the gate dielectric can provide the missing nonvolatility to the magnetoelectric effect and enhances its efficiency by an order of magnitude. We report the largest voltage-induced change to surface magnetic anisotropy yet demonstrated for a metallic thin film, and directly correlate this change with the density of trapped charge in an adjacent charge storage layer. This magnetoelectric charge-trap heterostructure provides a natural interface between conventional electronic and magnetic storage and logic devices, and the possibility to exploit nonvolatility in both the electronic and magnetic order offers the potential for multibit storage. 18 The functionality is similar to recently proposed ferroelectric/ferromagnetic stacks 19,20 but avoids the associated materials processing challenges by replacing the ferroelectric material with a well-established charge-trapping dielectric layer. Moreover, in the present implementation, charge trapping is optically assisted, providing a novel mechanism to optically manipulate the magnetic state. We use a simple capacitor de...

Thickness dependence of La0.7Sr0.3MnO3/PbZr0.2Ti0.8O3 magnetoelectric interfaces

“…Due to the linkage of Mn valence to LSMO magnetization, our research agrees with the work of others 19,35,36 that the screening of ferroelectric surface charge is likely the leading source of ME coupling at the interface. This hypothesis supports the report 37 that putting trapped charges in proximity of FM materials creates ME coupling effect. Our research also suggest single domain PZT is optimum for a large ME coupling effect to avoid in-plane domain structure.…”

Highly efficient voltage control of spin and enhanced interfacial perpendicular magnetic anisotropy in iridium-doped Fe/MgO magnetic tunnel junctions

“…The physical mechanisms of the purely electronic VCMA effect have been interpreted as the modification of the electronic structure at the interface through charge accumulation/depletion, [21][22][23] an electricfield-induced magnetic dipole 24 or the Rashba effect. 25 Chemical effects, such as a voltage-induced redox reaction, 26 or other electromigration 27 or charge trapping 28 effects can show a substantial VCMA coefficient of the order of a few thousands of fJ Vm − 1 , which is defined as the induced surface anisotropy energy change per unit electric field. However, these mechanisms have drawbacks of limited operational speed and writing endurance.…”

Large voltage-induced modification of spin-orbit torques in Pt/Co/GdOx

“…At the same time, since the anisotropy barrier determines the critical threshold for current-induced switching, it is desirable to lower PMA during switching and recover it afterwards. Voltage control of interfacial PMA has already been demonstrated based on charge accumulation at a ferromagnet/dielectric interface [19][20][21][22] and used for voltage-assisted spin-torque switching in magnetic tunnel junctions. [23][24][25] Since SOTs also derive from interfacial However, since the charge density in a metal is difficult to change significantly, effects based on voltage-induced electron accumulation are typically very small.…”