Abstract
Strongly out-of-equilibrium regimes in magnetic nanostructures exhibit novel properties, linked to the nonlinear nature of magnetization dynamics, which are of great fundamental and practical interest. Here, we demonstrate that field-driven ferromagnetic resonance can occur with substantial spatial coherency at unprecedented large angle of magnetization precessions, which is normally prevented by the onset of spin-wave instabilities and magnetization turbulent dynamics. Our results show that this limitation can be overcome in nanomagnets, where the geometric confinement drastically reduces the density of spin-wave modes. The obtained deeply nonlinear ferromagnetic resonance regime is probed by a new spectroscopic technique based on the application of a second excitation field. This enables to resonantly drive slow coherent magnetization nutations around the large angle periodic trajectory. Our experimental findings are well accounted for by an analytical model derived for systems with uniaxial symmetry. They also provide new means for controlling highly nonlinear magnetization dynamics in nanostructures, which open interesting applicative opportunities in the context of magnetic nanotechnologies.
Highlights
A central role is played by magnetic resonance spectroscopy, which includes various techniques such as nuclear magnetic resonance (NMR), electron paramagnetic resonance (EPR), and ferromagnetic resonance (FMR), all based on the excitation of the Larmor precession of magnetic moments around their equilibrium position [1]
We investigate the FMR of an individual nanodisc of yttrium iron garnet (YIG) in the perpendicular configuration
The accuracy of the latter to account for the experimental data means that the coherent precession of the magnetization vector is dominating the deeply nonlinear driven dynamics, despite the signatures of spin waves (SWs) instabilities observed at very large pumping power
Summary
The complexity of magnetization dynamics when strongly nonlinear regimes set in is usually detrimental to the reliable control of nanomagnetic devices, such as oscillators, memories, and logic gates In this respect, it is important to establish how far from equilibrium magnetic nanostructures can be driven before the coherent magnetization dynamics becomes highly perturbed by the onset of SW instabilities [19]. The experimental evidence of the coherence of large precessions is brought about by a new spectroscopic technique based on the application of a second probe excitation field, with frequency close to the one of the main time-harmonic field This second excitation is used to drive small eigenoscillations of magnetization around the FMR large-angle periodic oscillations, corresponding to coherent nutations of the magnetization.
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