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.

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.

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Time Resolved Magneto Optic Kerr Effect spectroscopy was used to all-optically study the dynamics in exchange coupled Fe(10 nm)/Pt(x = 0–5 nm)/FePt (10 nm) thin films. As the Pt spacer decreases, the effective magnetization of the layers is seen to evolve towards the strong coupling limit where the two films can be described by a single effective magnetization. The coupling begins at x = 1.5 nm and reaches a maximum exchange coupling constant of 2.89 erg/cm2 at x = 0 nm. The films are ferromagnetically coupled at all Pt thicknesses in the exchange coupled regime (x ≤ 1.5 nm). A procedure for extracting the interlayer exchange constant by measuring the magnetic precession frequencies at multiple applied fields and angles is outlined. The dynamics are well reproduced using micromagnetic simulations.

Magnetization dynamics of a Co/Ni multilayer film capped by a wedged Ta (0.3–1.3 nm) layer were investigated using time-resolved magneto-optic Kerr microscopy. The ferromagnetic resonance was observed for a wide range of magnetic fields in a variety of geometries. Using a macrospin approximation and the Kittel formula to evaluate the relaxation frequency, a significant increase of the effective anisotropy field was observed as the Ta layer thickness is increased. Furthermore, the damping behavior of the magnetization precession also shows a strong dependence on the Ta layer thickness. Using a model to account for variations of the local anisotropy fields, we reproduce the field evolution of the observed damping using a single Gilbert damping parameter for the Co/Ni system. These findings have direct implications for the rational design of novel spintronic devices.