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The effect of interlayer thickness on the magnetic properties of exchange-coupled composite media has been studied. Films consisting of a CoPtO hard magnetic layer and a CoCrPt soft layer separated by a Pt interlayer with a thickness varying from 0 to 40 Å have been fabricated. At low Pt thicknesses (<=16 Å) the exchange coupling forces the layers to switch as a single unit with a reduction in the hard magnetic layer coercivity of >2.5 kOe. Thicker Pt layers induce sufficient decoupling to permit each layer to reverse separately. The variation of the coercivity with Pt thickness is complex and suggests that the coupling between the layers is a combination of dipolar and exchange effects. [ABSTRACT FROM AUTHOR]

In this work, we report on the determination of the optimum level of SiO2 in (CoCrPt)1-x (SiO2)x perpendicular recording media. We have determined the optimum level via studies of magnetic viscosity which have been compared to recording properties. We find that the optimum level of SiO2 is of the order of 10%. At this level, studies of the activation volume of reversal show that the grains become essentially exchange decoupled and that a further increase in the level of SiO2 produces no further improvement in the decoupling. We also find that this level of SiO2 corresponds to optimum recording performance and that increasing the level of SiO2 further results in the production of a system with smaller grains where thermal loss is observed to increase dramatically. [ABSTRACT FROM AUTHOR]

FePt nanoparticles have the potential to extend the data density of magnetic recording beyond 1 Tbit/in². The phase transformation from low anisotropy, face-centered cubic to face-centered tetragonal with high anisotropy is essential and complex. The samples measured in this paper were annealed in a mixture with fine ground (<20 μm) NaCI. The switching field distributions and activation volumes of two different sizes of particles are presented, 4 and 15 nm. The samples exhibit complex structural behaviour, demonstrating how difficult it is to obtain uniform nanoparticles. We find that the 4-nm particles reverse coherently whereas the 15 nm do not due to inhomogeneous crystallinity. [ABSTRACT FROM AUTHOR]

CoPtCr-SiO2 perpendicular recording media with varying levels of SiO2 were examined by two different methods to determine the activation volume. The first is based on the sweep-rate dependence of the remanence coercivity using Sharrock's equation. The second is based on the measurement of the fluctuation field from time-dependence data, determined using a magneto-optical Kerr effect (MOKE) magnetometer. The values of Vact measured at the coercivity for both methods are almost the same, with the fluctuation field and activation volumes increasing with the SiO2 content. The difference between Vact and the grain volume measured directly from bright-field TEM images decreases as the SiO2 content increases due to the reduction of intergranular exchange coupling. The experimental results indicate that values of Vact obtained from single- and double-layered media are consistent. It was also found that the coercivity and normalized hysteresis loop slope at coercivity varied with SiO2 content, with the coercivity peaking at 8 at % SiO2 (nearly 26 vol% SiO2). [ABSTRACT FROM AUTHOR]

We discuss a method for the determination of activation volumes of reversal in perpendicular media. This method does not require correction for the self-demagnetizing field normally associated with these media. This is achieved by performing time dependence measurements at a constant level of magnetization. From the difference in time taken for the magnetization to decay to a fixed value at two fields separated by a small increment ΔH, the activation volume can be determined. We report data for both CoCrPt alloy films and a multilayer film, typical of those materials under consideration for use as perpendicular media. We find activation volumes that are consistent with the hysteresis curves of the materials. The activation volume scales qualitatively with the exchange coupling. The alloy films have significantly lower activation volumes, implying that they would be capable of supporting a higher data density [ABSTRACT FROM AUTHOR]