Ferromagnetic resonance linewidth and anisotropy dispersions in thin Fe films

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Abstract
In-plane ferromagnetic resonance (FMR) has been used to study the room-temperature linewidth ΔH of single crystal Fe films grown by dc magnetron sputtering onto MgO(100) substrates. Several samples were grown with the film thickness in the range 70 Å<tFe<250 Å. The measurements were carried out in the frequency range from 7.0 to 12.3 GHz. A phenomenological model for the FMR linewidth was developed that includes simultaneous effects due to intrinsic damping and angular dispersions of the cubic and uniaxial axes of anisotropy. These angular dispersions are found to be responsible for the relatively larger linewidths observed as a function of the in-plane field direction with fixed frequency, and as a function of frequency for the easy and hard directions as well. The behavior of the linewidth with the film thickness can be described by a sum of a constant volume term plus a term proportional to 1/tFe, representing the relaxation due to the misfit dislocations.