Low-Field Ferroelectric Switching realised by Forced Harmonic Oscillation of Domain Walls

Abstract

Conventionally, dc fields are used for switching dipole orientations in ferroelectrics. Such fields tilt the potential surface experienced by domain walls and thereby lower activation energies for their movement: escape from tilted potential wells is then realised by thermal excitation, allowing a "creep" process of pinning and depinning to develop. Borrowing ideas of domain wall resonance from the magnetic racetrack community, we show that ac fields, applied at the right frequency, can cause switching at much lower field magnitudes than dc ones (by factors of 4-5). Ferroelectric wall motion appears to be overdamped in the system studied (relaxor strontium barium niobate) and so the maximum in switching efficacy observed, at ~100 kHz, cannot be associated with resonant amplification, which needs an underdamped environment. Instead, in this high viscosity system, the frequency at which the maximum switching efficacy occurs seems to represent a compromise between the attempt frequency for wall depinning (which increases with frequency) and the extent to which energy is transferred to the wall within each field cycle (which decreases with frequency). Notwithstanding the absence of true resonance, the observation that ac excitation can dramatically reduce the bias levels needed for ferroelectric switching could still have significant ramifications for low energy memory technology.