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Magnetoelectric devices for spintronic applications

Christoph Adelmann^a, Davide Tierno^a, Hasnain Ahmad^a, Max Kouwenhoven^a,b, Tobias Jost^d, Moritz Geilen^d, Frederic Vanderveken^a,c, Giacomo Talmelli^a,c, Andrii Chumak^d, Philipp Pirro^d, Florin Ciubotaru^a, and Iuliana Radu^a

a Imec, Leuven, Belgium.
b TU Delft, Delft, The Netherlands
c KU Leuven, Leuven, Belgium.
d Technische Universität Kaiserslautern, Kaiserslautern, Germany.

Voltage-based magnetoelectric composites, consisting of both magnetostrictive as well as piezoelectric elements, offer an energy-efficient scalable approach to control the magnetization in nanostructures. In such a composite, the magnetization can be controlled by the strain induced in the piezoelectric element via the inverse magnetostriction effect. Although the basic concept has been discussed for decades, the application of magnetoelectric composite materials in micro- and nanostructures has only been achieved recently and a deeper understanding of the magnetoelectric coupling at the nanoscale is still missing.
In this presentation, we will review our recent work on micro- and nanoscale magnetoelectric devices. The DC magnetoelectric coupling was studied in Ni-PbZrTiO3 (Ni-PZT) magnetoelectric composites using anisotropic magnetoresistance (AMR). In such devices, a bias voltage is applied via two electrodes separated from a 1-μm-wide Ni stripe by 750-nm-wide gaps. The application of a DC voltage to the electrodes generates electric fringing fields in the PZT mesa and induces strain in the Ni stripe. The strain modifies the magnetoelastic anisotropy of the Ni stripe by inverse magnetostriction, which can be detected by AMR. To better understand the detailed device behavior, electrical measurements are complemented by finite-element simulations of the mechanical response of the system. Using this method, a magnetoelectric coupling coefficient of about 5200 (A/m)/V was determined, which is considerably larger than previously reported values for macroscopic devices. This demonstrates the potential of magnetoelectric composites for low-voltage spintronic applications at the nanoscale.
Furthermore, we have studied the magnetoelectric coupling at GHz frequencies in broadband magnetoelectric transducers. In such devices, the oscillating strain in a piezoelectric element couples to ferromagnetic resonance and propagating spin waves when transferred into a magnetostrictive element or waveguide. We demonstrate the generation of both hypersound (phonons) as well as spin waves in devices based on Ni/Py/BPZT compounds using Brillouin light scattering. Finite element simulations of the acoustic response of the structures indicate that the devices act as shear strain transducers. These results open the pathway towards the generation of magnetic oscillations using voltage signals.
This work has received funding from the European Union's Horizon 2020 research and innovation program within the FET-OPEN project CHIRON under grant agreement No. 801055.