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

Abstract

High field ferromagnetic resonance measurements of the anisotropy field of longitudinal recording thin-film media High frequency permeability of patterned spin valve type thin films Ferromagnetic resonance ͑FMR͒ 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 GHz͒ magnetic field is applied in the surface. An FMR simulator based on the Landau-Lifshitz-Gilbert equation confirms that the magnetic ͑exchange and/or magnetostatic͒ 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 GHz͒. The obtained H k is 7.0Ϯ0.2 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 dispersionϭ1.2Ϯ0.5kOe, Gilbert's damping constant ␣ϭ0.03Ϯ0.01, and a g valueϭ2.19Ϯ0.02.

High field ferromagnetic resonance measurements of the anisotropy field of longitudinal recording thin-film media

“…The FMR measurements on the media samples were carried out in the range of frequencies between 75 GHz and 93 GHz. In contrast to previously published results by Igarashi et al 17 we were able to obtain very well resolved resonance lines which allowed us to determine the resonance fields with a precision of better than Ϯ0.25%. Figure 6 illustrates an example of a first order derivative absorption line shape of high noise ͑sample 15A͒ media at 84 GHz.…”

Analysis of the Magnetic Anisotropy in Ba Ferrite Particles

“…Several experimental methods have been proposed to evaluate magnetic anisotropy. They include torque magnetometer curves [1], singular point detection [2], transverse susceptibility [3], rotational hysteresis [4], ferromagnetic resonance [5]. Such methods provide information on the mean anisotropy field.…”

Study of attempt frequency in Sharrock's formula for perpendicular recording hard disk media

“…Dt was the time step. The gyromagnetic ratio g of 1.92 Â 10 7 s À1 Oe À1 (the g-value of 2.19) and the Gilbert damping constant a of 0.05 were used [6].…”