Non-volatile switching of magnetism for reconfigurable microwave devices

The central challenge in tunable magnetic microwave devices lies in finding an energy efficient way to perform wide range ferromagnetic resonance (FMR) voltage tuning in a reversible and reproducible manner, rather than with a current-driven electromagnet.¹ Multiferroic heterostructures, exhibiting a strong strain-mediated magnetoelectric (ME) coupling between distinct ferromagnetic and ferroelectric phases, have shown great promise for frequency agile microwave applications. In these materials, a single control parameter of in situ voltage-induced piezo-strain, arising from ferroelectrics, is used to shift FMR frequency in elastically-coupled ferromagnetic phases via magnetoelastic effects.^{2, 3} Therefore, devices based upon such materials are, in principle, lightweight, fast, and energy efficient, overcoming some of the intrinsic limitations in conventional microwave components, while providing new functionality. However, in most prototype ME microwave devices, tuning of FMR frequency has been achieved through the use of a linear piezo response.^{4, 5} Upon removing the electric field, the FMR decays to the initial state. While these devices point towards a unique pathway for enhancing FMR tunability, reversible and non-volatile tuning of FMR using strain has remained relatively unexplored, and this is indispensable from a device application point of view. In this presentation, we will demonstrate three approaches to realizing non-volatile tuning FMR in microwave magnetoelectric composites. They are including 1) Ferroelastic domain dynamic switching in (011) oriented PMN-PT (0.71Pb(Mg1/3Nb2/3) O3-0.29PbTiO3) single crystal, that allows polarization vectors to rotate from an out-of-plane to a purely in-plane direction, thereby producing two distinct, stable and reversible lattice strain states. Voltage-impulse-induced non-volatile tuning of FMR can be realized in FeCoB/PMN-PT (011) through dynamic switching between these two distinct strain states as shown in Fig. 1. 2) Voltage induced 109° ferroelastic polarization switching in (001) oriented PZN-PT (0.93Pb(Zn1/3Nb2/3) O3-0.07PbTiO3) single crystal, that enables distinct lattice strain states in the in-plane diagonal directions ([110] or [1-10]), thereby results in the modulation of FMR in a stable and reproducible manner in FeGaB/PZN-PT (001) heterostructures.⁶ 3) Voltage-induced hysteretic phase transition in (011) oriented PZN-PT single crystal enables two reversible rhombohedral and orthorhombic stain states. Switching between these two states stimulated by voltage impulse, the FMR can be tuned non-volatilely in FeGaB/PZN-PT (011) heterostructures.⁵ These results point to opportunities for electrical tuning of strain sensitive properties in all materials and provide a framework for realizing reconfigurable, frequency agile, non-volatile and energy efficient electronics and microwave devices.