# Magnetically programmable surface acoustic wave filters: device concept and predictive modeling

## TL;DR

This paper introduces a new device concept for filtering sound waves using magnetic programming, with potential applications in science and industry.

## Contribution

The novel contribution is a programmable surface acoustic wave filter using magnetic state control and micromagnetic simulations.

## Key findings

- The device can achieve 52.0 dB/mm SAW transmission changes at 3.8 GHz based on magnetic alignment.
- Micromagnetic simulations show stray-field interactions between islets affect magnetoelastic coupling efficiency.
- A new numerical method extends energy conservation arguments for arbitrary magnetization patterns.

## Abstract

Filtering surface acoustic wave (SAW) signals of specified frequencies depending on the strength of an external magnetic field in a magnetostrictive material has garnered significant interest due to its potential scientific and industrial applications. Here, we propose a device that achieves selective SAW attenuation by instead programming its internal magnetic state. To this end, we perform micromagnetic simulations for the magnetoelastic interaction of the Rayleigh SAW mode with spin waves (SWs) in exchange-decoupled Co/Ni islets on a piezoelectric LiTaO3 substrate. Due to the islets exhibiting perpendicular magnetic anisotropy, the stray-field interaction between them leads to a shift in the SW dispersion depending on the magnetic alignment of neighboring islets. This significantly changes the efficiency of the magnetoelastic interaction at specified frequencies. We predict changes in SAW transmission of 52.0 dB/mm at 3.8 GHz depending on the state of the device. For the efficient simulation of the device, we extend a prior energy conservation argument based on analytical solutions of the SW to finite-difference numerical calculations, enabling the modeling of arbitrary magnetization patterns like the proposed islet-based design.