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An energy minimization and balancing approach is adopted to predict the occurrence of spike noise by obtaining estimates of the magnetostatic and total wall energy of a soft underlayer (SUL) for a given configuration of domain walls. The findings indicate that single-layer SULs are usually sources of spike noise unless their saturation magnetization is below 70-100 emu/cc.

Abstract: A micromagnetic numerical technique has been used to demonstrate how intergranular exchange coupling and intrinsic anisotropy field dispersion can be extracted from measuring two types of M–H curves. A realistic grain configuration formed by planar Voronoi cells is used to simulate perpendicular magnetic media. This technique effectively separates the effects of intergranular exchange coupling and anisotropy dispersion by finding their correlation to differentiated M–H curves with different initial magnetization states, even in the presence of thermal fluctuation. The validity of this method is investigated with a series of intergranular exchange couplings and anisotropy dispersions for different media thickness. A relationship between the auto-correlation function of an ac-erased sample and dispersion of the exchange interaction is demonstrated. Utilizing magnetization auto-correlation functions, the magnetic intergranular exchange coupling statistics show a correlation with the auto-correlation function shape in terms of zero-cross and undershoot values. [Copyright &y& Elsevier]

Abstract: Co/Pd multilayered media were improved using a three-fold approach. InSn seedlayers were used for higher coercivities, the Pd layers were doped with Si to decrease exchange between grains, and the Pd thickness was decreased to increase magnetization. When InSn seedlayers were used for these Co/Pd multilayered perpendicular magnetic recording media, the coercivity increased to measured values of 12.5kOe and projected values of almost 20kOe. These large values were obtained even though the depositions described here were done at room temperature. In order to lessen intergranular exchange coupling, Si (which has no solid solubility in Pd) was used to dope the Pd layers. Si also slightly decreased the grain size distribution to 23%. Initial recording measurements showed excellent signal to noise ratios, although an excessively wide switching field distribution prevented recording at the highest densities. Finally, the thickness of the Pd bilayers was reduced to increase the magnetization of the samples from 180 to 300emu/cm3. [Copyright &y& Elsevier]