High-Frequency Behavior and Damping of Fe Co N-Based High-Saturation Soft Magnetic Films
Thomas J. Silva, S X. Wang, Sun X. N., Anthony B. Kos
Magnetization dynamics measurements at subnanosecond time scale have been performed on Fe Co N high-saturation soft magnetic films with Permalloy nanolayer seeds and having a saturation magnetization of 1.9 MA/m (1900 emu/cm3). The damping parameter a varies from 0.011 to 0.018, depending on applied bias field. The peak frequencies of the imaginary permeability spectra and the zero-crossing frequencies of the real permeability spectra cannot be fitted with a fixed value of anisotropy field, indicating that the Kittel nist-equation is only qualitatively valid for these films. A phenomenological damping criterion is established based on a small-signal solution of the Landau Lifshitz Gilbert nist-equation: critical damping occurs in a soft magnetic film when the damping parameter is a= 2/sqrt(x0), where x0 is the initial permeability. The experimentally observed damping parameters are smaller than the critical value for the range of bias fields employed. The Fe Co N-based films have a ferromagnetic resonance frequency of 2 GHz at zero-bias field, showing great promise for applications in write heads and integrated inductors in a frequency range >1 GHz.