Damping Constant in Perpendicular Recording Media

Understanding the damping of magnetization precession in real magnetic recording media is of both fundamental and practical importance. In practical terms, the relaxation processes in media not only set a natural limit to recording data rates, but also play a critical role in microwave-assisted switching. This presentation reports on the damping in a commercial-like perpendicular media disk. The sample consists of a granular media layer and a soft capping layer and shows a coercivity of 5.2 kOe and a squareness of 0.97. The damping constant was determined through temperature- and frequency-dependent ferromagnetic resonance (FMR) measurements. The temperature-dependent FMR measurements were carried out with a 9.48 GHz cavity and magnetic fields oriented in a direction opposite to the remanent magnetization in the film. The temperature range was 110-320 K. The linewidth-temperature data were fitted with three models, the spin-flip magnon-electron scattering model, the breathing Fermi surface model, and inhomogeneity-associated line broadening. The fitting yields a $\alpha $ range of 0.07-0.15. The frequency-dependent FMR measurements were performed with a co-planar waveguide over a frequency range of 27.5-49.5 GHz. A linear fit to the linewidth-frequency data indicates a $\alpha $ value which is within the range determined from the temperature-dependent measurements.