Study on the Magnetic Microstructures for CoNiPt Thin Film Media by Rotational Hysteresis Loss Analysis

The magnetic microstructures in CoNiPt thin film media with coercivities ranging from 800 Oe to 1800 Oe were studied through rotational hysteresis loss analyses. In order to investigate the mechanism for the observed increase in coercivity, Hc was analyzed as a function of Hk(2¿), Hk^grain and Hp, determined by magnetic torque measurements. Here Hk(2¿) is the macroscopically induced uniaxial anisotropy field in the film plane, Hk^grain is the magnetic field for which the rotational hysteresis loss Wr vanishes in the high magnetic field region, and Hp is the magnetic field at which Wr is maximum. According to the results, Hc increases with Hp, remaining slightly higher than Hp, while Hk(2¿) and Hk^grain showed no systematic change and remained almost constant. These experimental facts suggest that Hc for these samples is mainly determined by the magnetization reversal of exchange-coupled crystallites, and Hc increases as a consequence of the reduction of intergranular exchange coupling. This behavior corresponds closely to the reduction in medium noise.