  The interaction between strain and spin has received intensive attention in
the scientific community due to its abundant physical phenomena and huge
technological impact. Until now, there is no experimental report on ultra-high
frequency magnetic resonance through the strain-spin coupling for any
technologically relevant perpendicular magnetic material. Here we report the
experimental detection of the acoustic strain waves that have a response time
on the order of 10 picoseconds in perpendicular magnetic [Co/Pd]n multilayers
via a femtosecond laser pulse excitation. Through direct measurements of
acoustic strain waves, we observe an ultra-high frequency magnetic resonance up
to 60 GHz in [Co/Pd]n multilayers. We further report a theoretical model of the
strain-spin interaction. Our model reveals that the energy could be transferred
efficiently from the strain to the spins and well explains the existence of a
steady resonance state through exciting the spin system. The physical origins
of the resonance between strain waves and magnetic precession and the requested
conditions for obtaining magnetic resonance within thin magnetic films have
also been discussed after thorough analysis. These combined results point out a
potential pathway to enable an extremely high frequency (EHF) magnetic
resonance through the strain-spin coupling.
