| Summary: | This study is focused on the characterisation of advanced perpendicular recording media. In particular, the distribution of the effective easy axis orientation and the effect of silica (SiO2) content on the magnetic properties have been investigated via magnetic measurements. The variation of coercivity (HC) as a function of angle has been used to determine the easy axis distribution. Due to the efficiency of the SiO2 segregation at the grain boundaries leading to intergranular exchange decoupling, the magnetisation reversal of each single domain particle can be described by a numerical simulation using Stoner Wohlfarth theory. The standard deviation of a Gaussian distribution of easy axis orientations in the calculations replicates the magnetic easy axis distribution in thin film media. Three types of media; granular, exchange coupled composite (ECC) and the combination of exchange coupled composite and a coupled granular continuous (CGC) film have been studied. The crystallographic orientation was also measured via X-ray rocking curves for a comparison to be made. It was found that the ECC media which have their grains almost completely segregated by SiO2 give an excellent fit to the simulation with σ = 5 degree. The results for granular and ECC/CGC media do not fit to the same level of accuracy. In-plane and cross-section TEM analysis of both samples show far from perfect segregation leading to intergranular exchange coupling. The activation volume has been used to study the effect of SiO2 content in ECC media. Vact and the physical grain volume have been investigated for identical structures with three different levels of SiO2. Time dependence measurements have been used to determine Vact. TEM analysis has been also carried out to investigate the grain size distribution and to examine the grain boundaries. Vact and the single grain volume are in excellent agreement for the sample with the highest SiO2 content, indicating complete exchange decoupling.
|
|---|
