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

Abstract

We realize resonant driving of the magnetization precession by monochromatic phonons in a thin ferromagnetic layer embedded into a phononic Fabry-Pérot resonator. A femtosecond laser pulse excites resonant phonon modes of the structure in the 10−40 GHz frequency range. By applying an external magnetic field, we tune the precession frequency relative to the frequency of the phonons localized in the cavity and observe an enormous increase in the amplitude of the magnetization precession when the frequencies of free magnetization precession and phonons localized in the cavity are equal. The continual miniaturization of magnetic devices down to the nanometer scale has opened new horizons in data storage [1], computing [2,3], sensing [4,5], and medical technologies [6]. Progress in nanomagnetism is stimulated by emerging technologies, where methods to control magnetic excitations on the nanometer spatial and picosecond temporal scales include optical [7,8], electrical [8], and micromechanical [9] techniques. To realize ultrafast nanomagnetism on the technological level, new physical principles to efficiently induce and control magnetic excitations are required, and this remains a challenging task. A new basic approach to this problem would be to explore nanoscale magnetic resonance phenomena-resonant driving and monitoring of magnetic excitations-which is widely used nowadays in traditional magnetism for microscopy, medicine, and spectroscopy. 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. Our device consists of a ferromagnetic layer embedded into a phonon Fabry-Pérot (FP) cavity. Such a cavity possesses quantized resonances for elastic waves (i.e., phonons) at f...

Ultrafast magnetoelastic probing of surface acoustic transients

“…4(c)] (M x → M x and M y → −M y , which is equivalent to φ → −φ), the direction of magnetization precession changes in accordance with the above equation. We note that the foregoing discussion on magnetoelasticity is related to a myriad of other ultrafast [17][18][19][20][21][22] work as well as its connection to quasistatic straintronics [23,24].…”

Laser-Induced Spatiotemporal Dynamics of Magnetic Films

“…This implies that phonons in magnets can be converted into magnetization and become detectable via magneto-optical [12][13][14] or electrical [15,16] techniques. In this Letter, we present a study of the spatial magnetization dynamics in magnetic thin films after focused-laser excitation [17].…”

“…A femtosecond laser pulse generates forces via the inverse Faraday effect [2,17,29] and heating [14,[30][31][32] that are instantaneous on the scale of the lattice and magnetization dynamics. The relative importance of these two mechanisms depends on the material and light and is still a matter of controversy.…”

A Topological View on Optical and Phononic Fabry–Perot Microcavities through the Su–Schrieffer–Heeger Model

“…By coupling several acoustic resonators, it is furthermore possible to generate effective phononic potentials and to study, e.g., Bloch oscillations of acoustic phonons [12,18,19]. From a more applied point of view, acoustic DBRs and cavities have been useful to demonstrate the enhancement of magnetic measurements [20], the control of emission of quantum-dot based lasers [21], and the amplification and stimulated emission of acoustic waves [16,22,23]. In a nutshell, the Fabry-Perot resonator demonstrated to be a versatile and useful structure in nanophononics.…”