Magnetoelectric devices for advanced spintronic applications

Spintronics is a novel field of electronics that uses the spin of electrons or the magnetization of thin magnetic films instead of the charge for memory, computation or sensor applications. Most of these device concepts are based on the magnetization control by electrical currents, such as spin-transfer torque or spin-orbit torque. The magnetization state is then determined either via magnetoresistance or the inverse spin-Hall effects. However, these reading mechanisms are based on electrical currents and are typically not energy efficient. To improve the read performance, the current resistance-based scheme needs to be replaced by a mechanism that generates a direct electrical signal. In particular, voltage-based schemes using magnetoelectric materials and compounds appear promising.

Magnetoelectric effects occur naturally in multiferroic materials but also in composite materials consisting of piezoelectric and magnetostrictive layers. In such composites, strong strain-induced magnetoelectric coupling can be observed. The coupling can be described by effective magnetoelastic fields that are generated in the magnetostrictive ferromagnetic layer(s) via application of stress due to the inverse magnetostriction (Villari) effect. The stress itself can be generated by an electric field applied across the piezoelectric layer(s). An inverse magnetoelectric effect also exists, which generates a voltage due to magnetization switching. The application of both the direct and the inverse effects in spintronic devices requires the detailed understanding and control of the direct and inverse magnetoelectric coupling in different geometries and different material systems.

The focus of the thesis is to investigate the potential to generate large voltage signals by the inverse magnetoelectric effect based on piezoelectricity and the magnetization switching and interaction with magnetic domain walls in nanomagnets. The study will include the patterning and the characterization of relevant materials on the nanoscale as well as the design, fabrication, and characterization of suitable devices. The work will be done in close collaboration with device engineers at imec working on magnetic memory and logic devices.

A background in (applied) physics, or nanotechnology is ideal, together with an interest in advanced spintronic applications and current topics in magnetism as well as enthusiasm for leading edge materials.