A high-amplitude microwave magnetic field localized at the nanoscale is a desirable tool for various applications within the rapidly developing field of nanomagnetism. Here, we drive magnetization precession by coherent phonons in a metal ferromagnetic nanograting and generate ac-magnetic induction with extremely high amplitude (up to 10 mT) and nanometer scale localization in the grating grooves. We trigger the magnetization by a laser pulse which excites localized surface acoustic waves. The developed technique has prospective uses in several areas of research and technology, including spatially resolved access to spin states for quantum technologies.The exploration of magnetism at the nanoscale continues to be a rapidly developing field. Magnetic recording with ultrahigh densities [1] for data storage, magnetic resonant imaging with nanometer resolution [2, 3] for medicine and biology, addressing the magnetic states of atoms [4][5][6][7][8] for quantum computing, and ultrasensitive magnetic sensing [9] are the most prominent examples within the multifaceted research field of nanomagnetism. Most of the proposed concepts and prototypes utilize oscillating (ac-) magnetic fields with frequencies from millions up to hundreds of billions of cycles per second (10 6 -10 11 Hz). The oscillating magnetic fields are used to override the coercivity of ferromagnetic grains [10], to set atomic magnetic moments to a desired state [2,3,9], and to encode quantum information into spin states [4][5][6][7][8]11]. These examples utilize conventional methods for the generation of ac-magnetic fields: an external rf-generator in combination with a microwire [2][3][4][5][9][10][11] or a microwave cavity [6][7][8]11]. This methodology cannot be applied at the nanometer scale. A key breakthrough would be nanoscale generation of high-amplitude, monochromatic ac-magnetic fields. This would open the possibility to address neighboring nano-objects, e.g. spin qubits, independently, and to reduce the energy consumption in magnetic devices. It is however a challenging task to reach this goal because current technologies do not allow one to control the frequency, bandwidth and amplitude of an ac-magnetic field on the nanoscale.An efficient way to generate a high-frequency ac magnetic field is to induce coherent magnetization precession in a ferromagnet. The magnetization of ferromagnetic metals may be as large as 2 T. Precessional motion with frequencies of 10 GHz allows the generation of highamplitude microwave magnetic fields on the picosecond time scale. The magnetization precession can be driven by dc-spin polarized currents [12]. This approach is realized in microwave generators based on spin torque nanooscillators, but has severe limitations, e.g. in combining large amplitudes and high frequencies [13]. Coherent phonons, bulk [14,15] or surface [16,17] acoustic waves, have been successfully used for exciting the magnetization precession in ferromagnetic films. The effect of a surface acoustic wave (SAW) on the magnetic order in a ferromag...

We demonstrate a variety of precessional responses of the magnetization to ultrafast optical excitation in nanolayers of Galfenol (Fe,Ga), which is a ferromagnetic material with large saturation magnetization and enhanced magnetostriction. The particular properties of Galfenol, including cubic magnetic anisotropy and weak damping, allow us to detect up to 6 magnon modes in a 120nm layer, and a single mode with effective damping α ef f = 0.005 and frequency up to 100 GHz in a 4nm layer. This is the highest frequency observed to date in time-resolved experiments with metallic ferromagnets. We predict that detection of magnetisation precession approaching THz frequencies should be possible with Galfenol nanolayers.

We demonstrate spin pumping, i.e. the generation of a pure spin current by precessing magnetization, without application of microwave radiation commonly used in spin pumping experiments. We use femtosecond laser pulses to simultaneously launch the magnetization precession in each of two ferromagnetic layers of a Galfenol-based spin valve and monitor the temporal evolution of the magnetizations. The spin currents generated by the precession cause a dynamic coupling of the two layers. This coupling has dissipative character and is especially efficient when the precession frequencies in the two layers are in resonance, where coupled modes with strongly different decay rates are formed.The generation of a spin current (SC) by magnetization precession (MP) is known as spin pumping (SP) [1]. Thereby, the precessing magnetization of a ferromagnetic (FM) film transfers angular momentum to an adjacent material, representing a pure SC that is not accompanied by the flow of charges. SCs generated by SP contain an ac-component at the precession frequency and carry also the MP phase. Conceptually, SP offers a new way of building spintronic devices by flexibly combining conducting and insulating materials [2][3][4][5][6][7][8]. This has stimulated intense efforts aimed at demonstrating SCs in a robust way [9].Conventional SP experiments exploit a ferromagnetic resonance (FMR) where the MP is driven by a microwave field [10]. The transfer of angular momentum to the adjacent material results in enhanced damping of the FMR [11,12] and thus to a broadening of the corresponding resonance spectrum [13,14]. In turn, the SC injected into the adjacent layer can be detected by, for example, the inverse spin Hall effect [2][3][4][5][6][7][8][15][16][17][18][19][20][21][22]. In a spin valve structure consisting of two FM layers separated by a nonmagnetic spacer, the SC generated by one layer drives the magnetization precession of the other layer [23][24][25][26]. At resonance, when the precession frequencies of the FM layers coincide, a strongly coupled collective precessional mode forms [27,28].This conventional approach has a drawback, however: applying monochromatic microwave fields for driving the MP lacks the flexibility required for nanoscale applications, it strictly sets the MP and SC phase, and requires exact matching to the FMR frequency. Ultrafast optical excitation, widely used nowadays in ultrafast optomagnetism for launching MPs [29], is a promising alternative. In metallic FMs, ultrashort laser pulses trigger MP by rapidly alternating the magnetic anisotropy [30]. While laser pulses have been utilized for SC generation via the transport of spin-polarized electrons from an opticallyexcited magnetic region [31][32][33][34][35][36], no evidence of pure SCs generated by optically launched MP has been reported.In this Letter, we report optically excited SP in a pseudo spin-valve (PSV) consisting of two FM layers separated by a normal metal spacer. By femtosecond laser pulses we simultaneously excite MP in the two magnetic layers...

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