Magnetization dynamics triggered by surface acoustic waves

Abstract

Investigations into fast magnetization switching are of both fundamental and technological interest. Here we present a low-power, remote method for strain driven magnetization switching. A surface acoustic wave propagates across an array of ferromagnetic elements, and the resultant strain switches the magnetization from the easy axis into the hard axis direction. Investigations as a function of applied magnetic field as well as unidirectional anisotropy (the exchange bias) reveal excellent agreement with prediction, confirming the viability of this method.

Irreversible magnetization switching using surface acoustic waves

“…During the growth, when atoms are mobile on the surface, nearest-neighbor Mn pairs on the GaAs (001) surface have a lower energy for the [1][2][3][4][5][6][7][8][9][10] direction compared to the [110] 39 .…”

“…Another route consists in generating strain through lower frequency (<2 GHz) surface acoustic waves (SAWs). On in-plane magnetized systems, SAWs have been used to drive ferromagnetic resonance in thin Ni films 4 , or periodically switch magnetization between hard and easy axes in Co bars 7 . Recent theoretical work has focused on the switching of in-plane Terfenol nanomagnets subjected to stress 8,9 , but no experimental or theoretical work has been shown on perpendicularly magnetized systems.…”

Surface-acoustic-wave-driven ferromagnetic resonance in (Ga,Mn)(As,P) epilayers

“…The opposite effect, inverse magnetostriction, whereby magnetization can be changed upon application of a strain, is particularly relevant to magnetic data storage technologies as a possible route towards induction-free data manipulation when used dynamically. It has been proposed for magnetization switching through resonant [2,3] or nonresonant processes [4,5], the latter possibly at play in early results of surface acoustic wave (SAW)-induced lowering of coercivity in Galfenol films [6]. In the case of precessional (resonant) switching, two features are necessary: sizable magnetoacoustic coupling (to trigger precession), and a highly nonlinear system (to force wide, noncircular precession needed for magnetization reversal).…”

Resonant driving of magnetization precession in a ferromagnetic layer by coherent monochromatic phonons

“…The typical frequencies f M of the magnetic resonances [e.g., the ferromagnetic resonance (FMR) in ferromagnetic and ferrimagnetic materials] are in the GHz and sub-THz frequency ranges. The traditional methods to scan magnetic excitations at these frequencies use microwaves, but due to the requirement of massive microwave resonators providing long wavelength radiation, they cannot provide high-speed control of magnetization locally on the nanoscale.Among various emerging techniques in nanomagnetism, the application of stress to magnetostrictive ferromagnetic layers has been shown to be an effective, low-power method for controlling magnetization: Applying in-plane stress in stationary experiments enables irreversible switching of the magnetization vector [10]; the injection of picosecond strain pulses induces free precession of the magnetization [11]; excitation of quantized elastic waves in a membrane enables driving of the magnetization at GHz phonon frequencies [12]; and surface acoustic waves can be used to control the magnetic dynamics in ferromagnetic nanostructures [13][14][15]. In the present Rapid Communication, we examine the interaction of a high-frequency (10−40 GHz) magnetic resonance in a magnetostrictive ferromagnetic film with an elastic harmonic excitation in the form of a localized phonon mode, and demonstrate how this interaction becomes significantly stronger at resonance conditions.…”