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As longitudinal magnetic recording media approach the superparamagnetic limit, temperature-dependent effects are becoming ever more important. This work reports an unexpected temperature dependence for the Sharrock stability parameter S typically given as KuV/kBT, where Ku is the uniaxial anisotropy, V the switching volume, kB is Boltzmann's constant, and T the temperature. Temperature-dependent vibrating sample magnetometer measurements were made of the saturation and remanent magnetization Ms and Mr, remanent coercivity Hcr, and Ku. The Sharrock equation was used to calculate S, and the time-independent switching field Ho of representative longitudinal recording media. Instead of the product SkBT decreasing proportionally to Ku or Ho with increasing temperature as initially expected, we find SkBT decreases at approximately half this rate.
Date of Publication: July 2004