Exchange spring magnets, consisting of a [Co(0.5 nm)/Pd(1 nm)]5 multilayer with
perpendicular magnetic anisotropy and a Co20Fe60B20 film with easy plane anisotropy, of
variable thickness tCFB, are investigated using Brillouin light scattering. On reducing tCFB in
the range 0.8–2.3 nm, the spin-wave frequency gap displays a remarkable increase from nearly
4–48 GHz, reflecting the corresponding rapid growth of the tilting angle of the magnetization
with respect to the film normal. These findings are interpreted using a one-dimensional
model in which each atomic layer is assumed to be uniformly magnetized, subjected to an
effective out-of-plane or easy-plane anisotropy depending on the layer position in the stack,
and exchange coupled to its two nearest neighbour atomic layers. With respect to previously
investigated [Co/Pd]-NiFe hybrid magnets, a largest frequency tunability, restricted to a
narrower range of the soft layer thickness, is observed.