# Unidirectional planar Hall voltages induced by surface acoustic waves in ferromagnetic thin films

## TL;DR

This study investigates surface acoustic wave-induced voltages in ferromagnetic thin films, revealing unique acoustoelectric effects, including unidirectional planar Hall voltages, with potential implications for spintronic devices.

## Contribution

It demonstrates the generation of unidirectional planar Hall voltages by surface acoustic waves in ferromagnetic films, a novel acoustoelectric phenomenon not previously reported.

## Key findings

- Longitudinal voltage scales linearly with SAW power.
- Transverse voltage depends on magnetic field angle, resembling planar Hall effect.
- Acoustic transverse resistance exceeds planar Hall resistance by over an order of magnitude.

## Abstract

The electromotive forces induced by surface acoustic waves (SAWs) are investigated in ferromagnetic thin films. CoFeB thin films deposited on LiNbO$_3$ substrates are patterned into Hall-bars to study the acoustoelectric transport properties of the device. The longitudinal and transverse dc voltages that develop in the Hall bars, which are parallel and orthogonal to the flow of the SAW, respectively, are measured under application of an in-plane magnetic field. The longitudinal voltage scales linearly with the SAW power and reverses its polarity upon changing the direction to which the SAW propagates, suggesting generation of a dc acoustic current via the SAW excitation. The magnetic field has little influence on the acoustic current. In contrast, the SAW induced transverse voltage shows significant dependence on the relative angle between the magnetic field and the SAW propagation direction. Such field angle dependent voltage resembles that of the planar Hall voltage induced by electric current. Interestingly, the angle dependent acoustic transverse voltage does not depend on the SAW propagation direction. Moreover, the magnitude of the equivalent angle dependent acoustic transverse resistance is more than one order of magnitude larger than that of the planar Hall resistance. These results show the unique acoustoelectric transport properties of ferromagnetic thin films.