Magnetization dynamics and static properties of Ho-doped Ni0.8Fe0.2

The effect of holmium (Ho) doping in films of Ni0.8Fe0.2 (NiFe) is investigated. The ferromagnetic resonance (FMR) is measured, and the linewidths (Delta f) are fit to a model that incorporates broadening from inhomogeneities and intrinsic damping (alpha(LLG)). The data reveal a drastic increase in Delta f for increasing Ho concentration in the NiFe films, while the fits of this data to the model indicate this is largely due to an increase in alpha(LLG). At Ho concentrations of 10% and greater, the saturation magnetization is reduced by more than 60% while the FMR is no longer observable, which is likely due to the signal falling below the noise floor from further linewidth broadening and decreased magnetization. In general, the saturation magnetization decreases continuously with Ho concentration, presumably due to local ferrimagnetic order induced by the Ho moments. However, the coercivity is essentially unchanged by the doping, while the magnetic anisotropy H-K is unchanged out to 2% Ho, beyond which there is an abrupt step-function-like increase. The data suggest Ho concentrations as small as 2% can substantially increase intrinsic damping in NiFe while minimizing change in other practical magnetic properties. (c) 2009 American Institute of Physics. [DOI: 10.1063/1.3081379]