Abstract
Since the work of Oersted and Ampère in the early 19th century, magnetism and magnetic fields have been connected to electric currents. By contrast, the control of magnetism by electric fields has elicited interest in the scientific and engineering communities only much more recently. Although originally postulated by Pierre Curie in 1894 and later discussed in more detail by Debye in the 1920s, the first experimental demonstration of a magnetoelectric effect occurred only in 1960. While single phase multiferroic materials were initially at the center of interest, the focus shifted rapidly in the 1970s towards magnetoelectric compound materials that offer larger magnetoelectric coupling strengths. Recently, magnetoelectricity has seen a renaissance due to both technological and theoretical progress [1,2]. The main interest in magnetoelectric systems lies in the potentially much higher energy efficiency with respect to current- and even current-density-based magnetization control. Therefore, magnetoelectricity may become an enabling step for novel low-power spintronic devices [3,4].
Magnetoelectric compound materials are layered composites that consist of piezoelectric and magnetostrictive films. The magnetoelectric coupling occurs via strain: applying an electric field across the piezoelectric generates strain, which is then transferred to the adjacent magnetostrictive. This leads to an effective magnetic field that can influence the magnetization of the system. An analogous inverse effect exists also that links changes in the magnetization direction to electric fields. Since the coupling between voltage and strain in piezoelectric films can be efficient, magnetoelectric composites are promising as transducers between electric and magnetic domains with high energy efficiency and large output signal.
For microelectronic applications, magnetoelectric composites must be integrated into devices and miniaturized to the nanoscale. In this presentation, we review our recent work on submicron magnetoelectric devices and discuss the effect of scale on the voltage coupling. We demonstrate that the miniaturization can lead to an enormous increase in the voltage response of magnetoelectric structures. Moreover, many applications require fast responses of the devices with targeted operational frequencies in the GHz range. Such high frequencies can strongly modify the mode of operation of magnetoelectric devices since the coupling may now occur between acoustic waves or resonator modes in nanoscale devices and dynamic magnetic excitation, such as ferromagnetic resonance or spin waves [5,6]. We introduce the basic concepts of magnetoelectric spin wave transducers and demonstrate their operation. Finally, we discuss the potential of magnetoelectric transducers for spin wave computing applications [7].
This work has been funded by the European Union's Horizon 2020 research and innovation program within the FET-OPEN Project CHIRON under Grant Agreement No. 801055as well as by imec's industrial affiliate program on beyond-CMOS logic.
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Figure: Top: Schematic of a nanoscale magnetoelectric spin wave transducer on top of a magnetostrictive waveguide including simulated strain tensor components due to resonator modes at 10 GHz. Bottom: Micromagnetic simulation results of the magnetization dynamics generated by a magnetoelectric transducers at 10 GHz [5].
Figure 1