Magnetoelectrics are a class of spintronic materials that have received particular attention due to their potential to manipulate magnets at very low power and the possibility for new functionalities. Besides multiferroic materials, which possess simultaneous magnetic and ferroelectric polarization, magnetoelectric composites have been at the center of research on magnetoelectricity for decades. Such composites consist of piezoelectric and magnetostrictive materials and rely on the interaction between the magnetization and mechanical degrees of freedom.

Applying an electric field to a piezoelectric material leads to the generation of a mechanical deformation (strain) that can be transferred to an adjacent magnetostrictive material. The strain inside the (ferromagnetic) magnetostrictive material leads then to a magnetoelastic effective magnetic field via the Villari effect (inverse magnetostriction) that can exert a torque on the magnetization. Conversely, the rotation of the magnetization in a magnetostrictive material generates strain that can lead to charge separation and an electric polarization in an adjacent piezoelectric material.

Magnetoelectric transducers
To build logic circuits based on spin-wave majority gates that are competitive with CMOS-based technology, it is necessary to develop energy efficient transducers between spin-wave and electric domains so to cointegrate the two technologies in a single system. Key requirements of such transducers are high coupling efficiency, low operational power, and high bandwidth. Magnetoelectric transducers represent a scalable and low-power alternative consisting of a piezoelectric-magnetostrictive (PE-MS) bilayer in which the coupling between the electric and the spin domain occurs via strain. (details: Tierno et al. Microelectronic Engineering 187–188 (2018)).

Of particular interest was the geometry of the transducer and the impact of the non-active surrounding layers on the effective magnetoelastic and magnetoelectric coupling. The “active” part of the structure consisted of a pillar including the magnetoelectric bilayer and two metal electrodes.

In the same way, the experimental device structure is based on a magnetoelectric pillar transducer. Functional ME spin wave transducers down to 500 nm CD and up to 10 GHz has already been demonstrated.