Determination of effective anisotropy in a modern particulate magnetic recording media

The dramatic increases achieved in the areal density of magnetic data storage systems depend crucially upon a commensurate reduction in the size of the particles that comprise modern recording media. When modelling the characteristics and performance during the continuing development of such high-performance media, it is essential that the effects of reduced magnetic particle dimensions be fully taken into account. An analytic technique is presented that facilitates determination of the effective anisotropy of the particulate media under investigation. The procedure is demonstrated using experimental data obtained from a series of mono-layer samples composed of single-domain cobalt nano-particles, in which the particle volumes and packing fractions are varied throughout the series. The particles, with diameters in the size range 6.2–9 nm, are determined to possess an effective anisotropy ≈7.9×106 erg/cm3 and a CoO outer shell of thickness 1.1 nm. When these values are utilised to construct a model describing the physical and magnetic properties of the samples, as a function of deposited Co volume thickness, then close correspondence is obtained between predicted and experimentally measured model descriptors.