Jason L. Pressesky

Cluster size and exchange dispersion in perpendicular magnetic media

A computational study of the effects of the intergranular exchange field and its dispersion on the cluster size in perpendicular recording media is presented. The dispersion arises from the grain size dispersion and the dispersion of intrinsic exchange coupling between individual grains. It is found that increasing the degree of dispersion reduces the cluster size due to weakly coupled grains acting as pinning sites against the expansion of the clusters. A simple semi-analytical model is proposed which gives good agreement with the numerical calculations in the limit of the large anisotropy constant.

Distribution of switching fields in magnetic granular materials

We present analytical calculations and kinetic Monte-Carlo modeling of rate-dependent behavior of switching field distributions (SFDs) in an ensemble of Stoner-Wohfarth particles, assuming distributions of anisotropies and volumes, and thermal activation included by the Neel-Brown theory. By applying probabilistic arguments, we show that the SFD can be self-consistently separated into the contribution from distributions of intrinsic properties of particles and the (irreducible) contribution resulting solely from thermal fluctuations, which is shown to become a significant effect at sweep rates relevant to the recording process. This provides a unifying framework for systematic analysis of different classes of systems.

Quadrature phase-shift interferometer (QPSI) decoding algorithms and error analysis

A He-Ne laser based Quadrature Phase Shift Interferometer (QPSI) has been developed for the topographic measurement of ultra-smooth surfaces, such as those used as magnetic recording disks. The design uses the polarization property of the light to create two independent interference signals, which are phase shifted by 90 degrees with respect to one another. Because the phase angle is the argument of a sine and cosine function, wrapping of the phase occurs, i.e., the interference amplitude is a periodic function of the phase. An unwrapping or decoding algorithm has been developed using the maximum/minimum intensity method. Finding accurate maximum and minimum values of the intensity signals is the key to minimizing the decoding error. An approach we have developed and describe here provides a more reliable method for finding the values of maximum and minimum intensity of the interference signals in order to create accurate intensity envelopes, which are required for the phase unwrapping algorithm. The decoding error of the algorithms has been evaluated with the synthetic waveforms, which are computer generated to simulate the interference signals from a disk surface with introduced amplitude modulation and phase angle error.