Improved Magnetic Information Storage using Return-Point Memory

The traditional magnetic storage mechanisms (both analog and digital) apply an external field signal H(t) to a hysteretic magnetic material, and read the remanent magnetization M(t), which is (roughly) proportional to H(t). We propose a new analog method of recovering the signal from the magnetic material, making use of the shape of the hysteresis loop M(H). The field H, ``stored'' in a region with N domains or particles, can be recovered with fluctuations of order 1/N using the new method - much superior to the 1/sqrt{N} fluctuations in traditional analog storage.Comment: 9 pages, 15 figure

Effects of structure on noise in very thin particulate data storage media

The effects of structure on noise in very thin particulate data storage tapes have been investigated using DC and tone-noise methods. The results from a set of five commercial development tapes indicate that large structural correlations of size ~ 5 μm become increasingly apparent as the magnetic layer of the tapes becomes thinner over the range 140 – 50 nm. As the samples were fabricated from identical particles (MP4 – length ~ 60nm) using the same double coating process, and with the tone-noise results showing comparable top surface roughness, these findings are consistent with large in-plane structures at the magnetic/non-magnetic interface that may be expected from mixing effects during production drying. Since this interface moves ever closer to the head with increasing data density, its effects on media noise will become increasingly important

ALSEP termination report

The Apollo Lunar Surface Experiments Package (ALSEP) final report was prepared when support operations were terminated September 30, 1977, and NASA discontinued the receiving and processing of scientific data transmitted from equipment deployed on the lunar surface. The ALSEP experiments (Apollo 11 to Apollo 17) are described and pertinent operational history is given for each experiment. The ALSEP data processing and distribution are described together with an extensive discussion on archiving. Engineering closeout tests and results are given, and the status and configuration of the experiments at termination are documented. Significant science findings are summarized by selected investigators. Significant operational data and recommendations are also included

TRANSVERSE SUSCEPTIBILITY STUDIES OF RECORDING MEDIA

A highly sensitive transverse susceptometer has been developed for the investigation of magnetic recording media. The susceptometer was based on the design of Pareti and Turilli[4] with modifications to the solenoid and sensing coils. The modifications have resulted in an improvement in the signal to baseline ratio of a factor of 525, and a reduction in random noise. The increase in the sensitivity of the susceptometer allowed the investigation of Advanced Metal Particle (AMP) tapes and the measurement of the imaginary component of the transverse susceptibility (TS) proposed by Papusoi[5]. Also, a modification was developed which allowed the investigation of the non-linear TS, proposed by Chantrell et al[7]. The work reported for the latter two techniques was the first experimental demonstration of these measurements on magnetic recording media. Samples of Co-y-Fe203, Cr02, mixed y-Fe203 / Cr02 and AMP tapes were investigated, as were y- Fe201, Cr0 2 and AMP powders. The investigations suggested that the incoherent reversal mode was dominant in the systems containing Cr02, with coherent reversal dominant in the remaining systems. The anisotropy peaks measured using the non-linear IS were found to be less dependent on sample texture than those of the traditional linear measurement. In particular the anisotropy peaks of the non-linear TS for incoherently reversing systems appeared to be independent of texture and it was proposed that these were a direct measure of the anisotropy field distribution, although independent verification was not performed. The determination of magnetic coating thickness after Sollis and Bissell[6] was extended to allow the measurement of AMP tapes. A computer model was developed to investigate the error in the technique due to the particulate nature of the coating. The results of the model indicated that the error increased as coating thickness and volume packing fraction decreased. Correction factors were determined for MP3 and MP4 particle based systems. The detection of the imaginary component of TS and its close agreement with the theoretical predictions of Papusoi suggested that the dassification of TS as a 'stiffness' method of anisotropy field determination might be in error

Models of microstructure and magnetic properties for magnetic recording media

Three computational models have been developed to simulate magnetic properties of granular media, particulate media microstructures and self-assembled systems. The granular media model uses an energy minimisation approach to describe the magnetic properties of a system of randomly oriented single-domain particles taking into account dipolar and exchange interactions as well as thermal effects. At low temperature dipolar interactions produce flux closure vortex structures leading to a decrease of both remanence and coercivity. When thermal effects become important, dipolar interactions lead to an increase of the local energy barriers increasing both remanence and coercivity as compared to the superparamagnetic case. Exchange coupling tends to align the magnetic moments producing an increase in the remanence of such systems while cooperative reversals decrease their coercivity. The particulate media model uses a spherocylindrical approximation for the elongated magnetic particles that are used in tapes. The particles are allowed to move in a viscous solvent under the action of steric and magnetic interactions and of the orienting field. A percentage of the particles are grouped in clusters that behave as rigid bodies during the simulation. The results obtained suggest that the presence of the clusters leads to a disruption in the alignment of the free particles regardless of the cluster size. A third model uses a Monte-Carlo approach to describe the self-assembly process that occurs in surfactant coated magnetic particles. As the solvent dries the particles form assemblies to minimize the interaction energy. In order to obtain long-range self-assembled systems the particle areal density must be in a narrow range and the particle size distribution must have a standard deviation below 5%. The occurrence of local self-assembly is due to the presence of an attraction term in the interparticle interaction potential. The conditions under which square vs. hexagonal lattice can be obtained are discussed

Anisotropy and texture studies in magnetic media

The rapid development of magnetic materials for recording media applications increased the demands for new and more precise experimental investigation techniques. In respect with these demands, this project is focused on experimental analyses of advanced particulate media and magnetic thin film samples. A new extended rotational remanence technique for anisotropy field measurements was developed. The technique is suitable for samples that contain aligned or partially aligned particles and provides both: in-plane anisotropy field distributions and the in-plane anisotropy field. This technique was also extended to out-of-plane anisotropy field measurements. Rotational hysteresis was introduced as an alternative method for anisotropy field measurements. This applies well in the case of samples without texture or samples having very small magnetic moment (i.e. thin films). The two techniques for anisotropy field measurement compare well and the experimental results were interpreted in terms of inter-particles interactions. Two measurement methods for determination of the demagnetizing field acting perpendicular to a sample plane were also developed. The first method is based on the in-plane and out-of-plane anisotropy field determination using an extended rotational remanence technique. The second method can provide the demagnetizing field starting from in-plane and out-of-plane transverse hysteresis loops. Comparison between the results from the two methods showed good agreement. Furthermore, the demagnetizing field values were used to calculate the magnetic coating thickness, so the two methods provide a non-destructive method for magnetic thickness measurements in film samples. The in-plane easy axis distribution (EAD) was experimentally determined using vector VSM techniques. Correlations between in-plane tape texture and magnetic thickness were obtained for a series of advanced MP tapes. A theoretical approach was used in order to relate the orientation ratio to EAD. The out-of-plane EAD was derived from numerical calculations. The out-of-plane distribution also showed a variation with the magnetic thickness. In addition, the microstructure and particle morphology of the advanced MP tapes, as well as the out-of-plane component of magnetization, have been investigated using Mossbauer Spectroscopy. Finally, 3D - EAD maps were produced. All VSM experiments were fully computer controlled and the routines were designed in the LabView environment as part of this project