Coherent high-amplitude precession of the magnetization and spin waves with frequencies up to 40 GHz are generated by injecting picosecond compressive and shear acoustic pulses into nanometer-sized galfenol (Fe81Ga19) films. The magnetization modulation is due to the picosecond inverse magnetostrictive effect. The oscillations of the magnetization measured by magneto-optical Kerr rotation last for several nanoseconds, and the maximum modulation of the in-plane effective magnetic field is as high as 40 mT. These results in combination with a comprehensive theoretical analysis show that galfenol films possess excellent properties for ultrafast magnetization control based on the picosecond inverse magnetostrictive effect.

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...

Quasi-longitudinal and quasi-transverse picosecond strain pulses injected into a ferromagnetic (311) (Ga,Mn)As film induce dynamical shear strain in the film, thereby modulating the magnetic anisotropy and inducing resonant precession of the magnetization at a frequency ~10 GHz. The modulation of the out-of-plane magnetization component by the quasitransverse strain reaches amplitudes as large as 10% of the equilibrium magnetization. Our theoretical analysis is in good agreement with the observed results, thus providing a strategy for ultrafast magnetization control in ferromagnetic films by strain pulses.

By means of a metal opto-acoustic transducer we generate quasi-longitudinal and quasi-transverse picosecond strain pulses in a (311)-GaAs substrate and monitor their propagation by picosecond acoustic interferometry. By probing at the sample side opposite to the transducer the signals related to the compressive and shear strain pulses can be separated in time. In addition to conventional monitoring of the reflected probe light intensity we monitor also the polarization rotation of the optical probe beam. This polarimetric technique results in improved sensitivity of detection and provides comprehensive information about the elasto-optical anisotropy. The experimental observations are in a good agreement with a theoretical analysis.

Coherent sub-THz phonons incident on a gold grating that is deposited on a dielectric substrate undergo diffraction and thereby induce an alteration of the surface plasmon-polariton resonance. This results in efficient high-frequency modulation (up to 110 GHz) of the structure's reflectivity for visible light in the vicinity of the plasmon-polariton resonance. High modulation efficiency is achieved by designing a periodic nanostructure which provides both plasmon-polariton and phonon resonances. Our theoretical analysis shows that the dynamical alteration of the plasmon-polariton resonance is governed by modulation of the slit widths within the grating at the frequencies of higher-order phonon resonances. PACS numbers: 73.20.Mf, 78.20.hc Creating new devices based on plasmonic nanostructures (PNs) requires development of new physical concepts where the properties of plasmons and their interaction with photons may be controlled externally. Several methods of this "active plasmonics" 1,2 were reported where the energy and propagation of plasmons were controlled by temperature 3 , optical excitation 4,5 , electric 6 and magnetic fields 7-9 . In order to explore the properties of plasmons in nanodevices it is necessary to realize nondestructive control of plasmons on timescales far below 1 ns. In particular, such techniques could be employed in recently developed plasmon lasers (spasers), to enhance their functionality 10,11 . Only then the advantage of plasmonics as compared traditional integrated electronics may be indeed exploited. By now there are a number of works where ultrafast control of plasmons in PNs has been demonstrated using femtosecond optical excitation 12,13 which possess a number of undesirable side effects, like thermal heating or excitation of high-energy electron states. Besides modulation of the PN dielectric function, plasmonic states may be controlled by modulation of the geometrical parameters of the PN, like size of elements or distances between elements. This can be realized by applying uniaxial stress 14,15 and, for dynamical modulation, acoustic waves may be used. The feasibility of such an acoustic approach for the modulation of plasmonic properties has been already shown in a number of recent works, where THz phonons interact with the plasmon resonance in a very small noble metal particle 16,17 , or in periodic structures but in the frequency range up to 10 GHz 18-20 .The aim of the present work is to realize an efficient modulation by sub-THz coherent phonons in a PN which has a narrow band plasmon-polariton resonance in the k 0 E α d G o ld G a d o li n iu m G a ll iu m G a r n e t AFM-Image 750 800 850 900 4°2°6°8°1 0°D etection Glanpolarizer λ/2 t 0 =78 ns BBO Beamsplitter q=2π n/d Strain-Pulse α Regenerative Amplifier 800 nm (a) (b) (c) r h α = Augrating GGG Al x y z T=5 K Reflected intensity R 0 Wavelength (nm) [111] 400nm 0 1 2 3 FIG. 1. (a) The scheme of the sample and AFM image of the grating. (b) The reflectivity spectrum for p-polarized white light from the Au grating on G...