Polaritons are widely investigated quasiparticles with fundamental and technological significance due to their unique properties. They have been studied most extensively in semiconductors when photons interact with various elementary excitations. However, other strongly coupled excitations demonstrate similar dynamics. Specifically, when magnon and phonon modes are coupled, a hybridized magnon–phonon quasiparticle can form. Here, we report on the direct observation of coupled magnon–phonon dynamics within a single thin nickel nanomagnet. We develop an analytic description to model the dynamics in two dimensions, enabling us to isolate the parameters influencing the frequency splitting. Furthermore, we demonstrate tuning of the magnon–phonon interaction into the strong coupling regime via the orientation of the applied magnetic field.

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We report a novel all-optical technique to drive and probe the spin dynamics of single nanomagnets. Optically generated surface acoustic waves (SAWs) drive the magnetization precession in nanomagnets via magneto-elastic (MEL) coupling. We investigate the field-swept dynamics of isolated Ni nanomagnets at various SAW frequencies, and show that this method can be used to accurately determine the intrinsic Gilbert damping of nanostructured magnetic materials. This technique opens a new avenue for studying the spin dynamics of nanoscale devices using non-thermal ("cold") excitation, enabling direct observation of the MEL driven dynamics.

The effect of the nanoscale array geometry on the interaction between optically generated surface acoustic waves (SAWs) and nanomagnet dynamics is investigated using Time-Resolved Magneto-Optical Kerr Effect Microscopy (TR-MOKE). It is demonstrated that altering the nanomagnet geometry from a periodic to a randomized aperiodic pattern effectively removes the magneto-elastic effect of SAWs on the magnetization dynamics. The efficiency of this method depends on the extent of any residual spatial correlations and is quantified by spatial Fourier analysis of the two structures. Randomization allows observation and extraction of intrinsic magnetic parameters such as spin wave frequencies and damping to be resolvable using alloptical methods, enabling the conclusion that the fabrication process does not affect the damping.