We report on room temperature
ferromagnetic resonance (FMR) studies of [ t Co|2t Ni] × N
sputtered films, where 0.1 ≤ t ≤ 0.6 nm. Two series of
films were investigated: films with the same number of Co|Ni bilayer
repeats (N = 12), and samples in which the overall magnetic layer
thickness is kept constant at 3.6 nm (N = 1.2/t). The FMR
measurements were conducted with a high frequency broadband
coplanar waveguide up to 50 GHz using a flip-chip method. The
resonance field and the full width at half maximum were measured
as a function of frequency for the field in-plane and field normal
to the plane, and as a function of angle to the plane for several
frequencies. For both sets of films, we find evidence for the
presence of first and second order anisotropy constants, K
1 and
K
2. The anisotropy constants are strongly dependent on the
thickness t, and to a lesser extent on the total thickness of
the magnetic multilayer. The Landé g-factor increases with
decreasing t and is practically independent of the multilayer
thickness. The magnetic damping parameter α, estimated from
the linear dependence of the linewidth ΔH, on
frequency, in the field in-plane geometry, increases with
decreasing t. This behaviour is attributed to an enhancement of
spin-orbit interactions with decreasing Co layer thickness and in thinner films,
to a spin-pumping contribution to the damping.
PACS. 76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance - 75.30.Gw Magnetic anisotropy - 75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)