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No description available.

No description available.

FMR spectroscopy is widely used for the characterization of many types of magnetic materials for use in an extensive range of applications. It is a powerful tool for probing both the magnetic properties and physical aspects of a material. In recent years in particular, there has been some interest in its use to study commercial recording media. However, there are a number of limitations inherent in the conventional method of observing FMR that restricts its usefulness and popularity as a research technique. The high, single frequency operation of the spectrometer makes broadband, frequency dependent measurements and studies of the unsaturated state of materials impractical. It also severely limits the quantity of data available making the analysis and interpretation difficult and prone to error. Additional complexities are encountered since the swept field technique means that a sample is subjected to a constantly changing magnetic environment which may not be ideal, especially for broad linewidth materials. A need, therefore, has been identified for an FMR technique capable of producing both swept field and swept frequency spectra over a wide range of frequencies. The design and development of a novel broadband FMR spectrometer is described in this thesis. The new technique has several advantages over similar methods presented in the literature. It can be applied over a very wide frequency range, dependent on the types of materials, for a variety of different FMR studies. The spectrometer itself is straightforward and easy to use and the resulting spectra (which show excellent agreement with equivalent conventional data) may be interpreted using the same models already used in FMR research. Most importantly, the simplicity of this spectrometer design means that it can be readily implemented in any reasonably equipped magnetics or microwave laboratory without the need for specific expertise or equipment. A preliminary broadband FMR study of magnetic recording media demonstrates the potential of the new technique both for more detailed characterizations of magnetic materials and for greater understanding of the ferromagnetic resonant effect itself.

Presented here are micromagnetic simulations to investigate alternative magnetic recording technologies including bit patterned media and domain wall storage. I have used a finite element/boundary element method to investigate the dynamics of the write process in magnetic recording systems; and a nudged elastic band method is used to calculate the thermal stability of written bits. Microwave assisted magnetization reversal of single phase media and exchange spring media is investigated. A reduction of the switching field by about a factor of two can be found in both single phase and exchange spring media when the microwave field reaches an amplitude that is 12 percent of the remanent coercivity without microwave assist. Furthermore, layer-selective writing of two-layer bitpatterned media is demonstrated by employing microwave assist technique. Selectivity is achieved by controlling the frequency of an oscillating magnetic field in the GHz range, applied in addition to the head field. Generation of the microwave field by means of a wire next to the tip of a single pole head is proposed. Optimization of writing heads is performed using micromagnetics and surrogate optimization. The shape of the pole tip is optimized for bit patterned, exchange spring recording media. I computed the write error rate and the adjacent track erasure for different maximum anisotropy in the multilayer, graded media. The results show a linear trade off between the error rate and the number of passes. Finally I have calculated magneto static fields from transverse and vortex magnetic domain walls in a planar Ni81Fe19 nanowire. These calculations indicate the required sensitivity of a nearby sensor for detecting either a domain wall of any type or being able to distinguish the domain wall character. Optimization of writing heads is performed using micromagnetics and surrogate optimization. The shape of the pole tip is optimized for bit patterned, exchange spring recording media. I computed the write error rate and the adjacent track erasure for different maximum anisotropy in the multilayer, graded media. The results show a linear trade off between the error rate and the number of passes. Finally I have calculated magneto static fields from transverse and vortex magnetic domain walls in a planar Ni81Fe19 nanowire. These calculations indicate the required sensitivity of a nearby sensor for detecting either a domain wall of any type or being able to distinguish the domain wall character.

The tribology of linear tape storage system including Linear Tape Open (LTO) and Travan5 was investigated by combining X-ray Photoelectron Spectroscopy (XPS), Augar Electron Spectroscopy (AES), Optical Microscopy and Atomic Force Microscopy (AFM) technologies. The purpose of this study was to understand the tribology mechanism of linear tape systems then projected recording densities may be achieved in future systems. Water vapour pressure or Normalized Water Content (NWC) rather than the Relative Humidity (RH) values (as are used almost universally in this field) determined the extent of PTR and stain (if produced) in linear heads. Approximately linear dependencies were found for saturated PTR increasing with normalized water content increasing over the range studied using the same tape. The stain formation mechanism had been identified. Adhesive bond formation is a chemical process that is governed by temperature. Thus the higher the contact pressure, the higher the contact temperature in the interface of head and tape, was produced higher the probability of adhesive bond formation and the greater the amount of transferred material (stain). Water molecules at the interface saturate the surface bonds and makes adhesive junctions less likely. Tape polymeric binder formulation also has a significant role in stain formation, with the latest generation binders producing less transfer of material. This is almost certainly due to higher cohesive bonds within the body of the magnetic layer. The lower contact pressure of the LTO system comparing with the Travan5 system ensures that fewer and smaller three-body abrasive particles were swept across the poles and insulator regions. Hence, lower contact pressure, as well as reducing stain in the same time significantly reduces PTR in the LTO system.

The increasing demand for high capacity data storage requires decreasing the head-to-tape gap and reducing the track width. A problem very often encountered is the development of adhesive debris on the heads at low humidity and high temperatures that can lead to an increase of space between the head and media, and thus a decrease in the playback signal. The influence of stains on the playback signal of reading heads is studied using RAW (Read After Write) tests and their influence on the wear of the heads by using indentation technique. The playback signal has been found to vary and the errors to increase as stains form a patchy pattern and grow in size to form a continuous layer. The indentation technique shows that stains reduce the wear rate of the heads. In addition, the wear tends to be more pronounced at the leading edge of the head compared to the trailing one. Chemical analysis of the stains using ferrite samples in conjunction with MP (metal particulate) tapes shows that stains contain iron particles and polymeric binder transferred from the MP tape. The chemical anchors in the binder used to grip the iron particles now react with the ferrite surface to create strong chemical bonds. At high humidity, a thin layer of iron oxyhydroxide forms on the surface of the ferrite. This soft material increases the wear rate and so reduces the amount of stain present on the heads. The stability of the binder under high humidity and under high temperature as well as the chemical reactions that might occur on the ferrite poles of the heads influences the dynamic behaviour of stains. A model of stain formation taking into account the channels of binder degradation and evolution upon different environmental conditions is proposed.