  Non-collinear magnets exhibit a rich array of dynamic properties at microwave
frequencies. They can host nanometre-scale topological textures known as
skyrmions, whose spin resonances are expected to be highly sensitive to their
local magnetic environment. Here, we report a magnetic resonance study of an
[Ir/Fe/Co/Pt] multilayer hosting N\'eel skyrmions at room temperature.
Experiments reveal two distinct resonances of the skyrmion phase during
in-plane ac excitation, with frequencies between 6-12 GHz. Complementary
micromagnetic simulations indicate that the net magnetic dipole moment rotates
counterclockwise (CCW) during both resonances. The magnon probability
distribution for the lower-frequency resonance is localised within isolated
skyrmions, unlike the higher-frequency mode which principally originates from
areas between skyrmions. However, the properties of both modes depend
sensitively on the out-of-plane dipolar coupling, which is controlled via the
ferromagnetic layer spacing in our heterostructures. The gyrations of stable
isolated skyrmions reported in this room temperature study encourage the
development of new material platforms and applications based on skyrmion
resonances. Moreover, our material architecture enables the resonance spectra
to be tuned, thus extending the functionality of such applications over a
broadband frequency range.
