A method of measuring anisotropy field of polycrystalline thin-film media

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Abstract
Ferromagnetic resonance (FMR) is used to measure the magnetic anisotropy field H k and its dispersion of poly-crystalline recording media. This method does not use any single crystal substrate. A high-intensity field is applied vertically to a sample surface to completely saturate the magnetization and a high-frequency (over 50 GHz) magnetic field is applied in the surface. An FMR simulator based on the Landau–Lifshitz–Gilbert equation confirms that the magnetic (exchange and/or magnetostatic) interactions have very little effect on the resonant frequency in the configuration used. The linewidth of the FMR spectrum is affected by the H k dispersion and damping constant. Methods using a torque or magnetization curve include magnetic interactions, resulting in a systematic error to the value of H k . This FMR method is applied to CoCrPt-alloy thin-film media with a Cr-alloy underlayer grown on a glass substrate. A conventional torque method is also used for comparison. The axis of hexagonal-close-packed Co magnetic grain is distributed at random in the surface. In an FMR measurement, external magnetic field is applied vertically to the surface up to 55 kOe for two frequencies (71 and 117 GHz). The obtained H k is 7.0±0.2 kOe, which is a little higher than the H k of 6.4 kOe estimated with the torque loss method. Important physical parameters that affect the recording performance are also estimated using the linewidth of FMR spectra for different frequencies with a micromagnetic simulation: H k dispersion =1.2±0.5 kOe , Gilbert’s damping constant α=0.03±0.01, and a g value =2.19±0.02.