https://doi.org/10.1140/epjb/e2007-00071-1
Ferromagnetic resonance study of sputtered Co|Ni multilayers
1
Department of Physics, New York University, 4 Washington Place, New York, NY, 10003, USA
2
Brookhaven National Laboratory, Upton, New York, 11973, USA
3
IBM T. J. Watson Research Center, Yorktown Heights, NY, 10598, USA
Corresponding authors: a jmb22@nyu.edu - b andy.kent@nyu.edu
Received:
1
October
2006
Revised:
9
February
2007
Published online:
14
March
2007
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, K1 and K2. 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)
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag, 2007