Temperature dependence of the magnetization reversal of thin-film longitudinal magnetic recording media

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 K_uV/k_BT, where K_u is the uniaxial anisotropy, V the switching volume, k_B is Boltzmann's constant, and T the temperature. Temperature-dependent vibrating sample magnetometer measurements were made of the saturation and remanent magnetization M_s and M_r, remanent coercivity H_cr, and K_u. The Sharrock equation was used to calculate S, and the time-independent switching field H_o of representative longitudinal recording media. Instead of the product Sk_BT decreasing proportionally to K_u or H_o with increasing temperature as initially expected, we find Sk_BT decreases at approximately half this rate.