Investigations of the Physical and Magnetic Microstructure of CoCr Thin Film Perpendicular Magnetic Recording Media

[摘要] The work presented in this thesis is concerned with improving the understanding of the relationship between the physical and magnetic microstructure in CoCr thin film perpendicular magnetic recording media. This was investigated using a combination of transmission electron microscope (TEM) techniques to study a series of CoCr films with systematically adjusted growth conditions. The first chapter begins with an outline of basic ferromagnetism and the energy considerations governing the domain configuration in ferromagnetic thin films. General principles of magnetic recording are then discussed, with a more detailed treatment of media, high density recording formats and the properties of CoCr for perpendicular recording. Chapter 2 introduces basic TEM imaging theory and describes the conventional transmission electron microscopes (CTEM's) and the dedicated scanning transmission electron microscope (STEM) used in this project. The chapter then discusses techniques for imaging magnetic structures and the use of high resolution energy dispersive x-ray (EDX) microanalysis in the STEM for microcompositional investigations. The first sections in chapter 3 discuss the planar and cross-sectional specimen preparation techniques adopted for all the work in this thesis. The remainder of the chapter describes the study of a series of CoCr layers grown to various thicknesses and with different compositions. Bulk physical and magnetic characterisation are combined with microstructural investigations in the CTEM. The work demonstrates that bulk measurements alone are insufficient to predict the physical, and therefore the magnetic microstructure, of CoCr thin films. It also illustrates the usefulness of such a study as part of any investigation of the microscopic properties of CoCr recording media. The next three chapters contain the experimental results which form the core of the thesis. Chapter 4 describes the experiments conducted on CoCr films using EDX microanalysis. Planar sections were investigated to allow correct positioning of the probe on a particular region of specimen and thus reveal, directly, the local elemental composition associated with features of the microstructure. Study was made of films deposited at different substrate temperatures both with and without a Ge underlayer. The results obtained using this technique provided detailed quantitative data on the extent and pattern of Cr segregation in each film. Chapter 5 describes the improvements in the differential phase contrast (DPC) mode of Lorentz microscopy in the STEM which facilitated simultaneous imaging of the physical and magnetic microstructure of thinned cross-sections of CoCr films. The results from the application of this technique to the study of the effect on the microstructure of substrate temperature during deposition are then interpreted in conjunction with the compositional information from chapter 4. The importance of direct microscopic study of recorded tracks in CoCr perpendicular recording media forms the introduction for chapter 6. The chapter then explains the development and results of a successful method for direct observation of the tracks with the Fresnel mode of Lorentz microscopy in the JEOL 2000FX TEM. The final chapter draws conclusions on the results of the project and presents proposals for possible future investigations of CoCr perpendicular magnetic recording media.

[发布机构] University:University of Glasgow

[关键词] Condensed matter physics, Electromagnetics