Book contents
- Frontmatter
- Contents
- Preface
- 1 Overview of Optical Data Storage
- 2 Optics of Gaussian Beams
- 3 Theory of Diffraction
- 4 Diffraction of Gaussian Beams from Sharp Edges
- 5 Optics of Thin Films and Multilayers
- 6 Magneto-optical Readout
- 7 Effects of High-numerical-aperture Focusing on the State of Polarization
- 8 Computer Modeling of the Optical Path
- 9 Noise in Magneto-optical Readout
- 10 Modulation Coding and Error Correction
- 11 Thermal Aspects of Magneto-optical Recording
- 12 Fundamentals of Magnetism and Magnetic Materials
- 13 Magnetostatics of Thin-film Magneto-optical Media
- 14 Mean-field Analysis of Amorphous Rare Earth–Transition Metal Alloys
- 15 Magnetization Dynamics
- 16 Origins of Coercivity
- 17 The Process of Thermomagnetic Recording
- 18 Media Characterization
- References
- Index
16 - Origins of Coercivity
Published online by Cambridge University Press: 07 September 2010
- Frontmatter
- Contents
- Preface
- 1 Overview of Optical Data Storage
- 2 Optics of Gaussian Beams
- 3 Theory of Diffraction
- 4 Diffraction of Gaussian Beams from Sharp Edges
- 5 Optics of Thin Films and Multilayers
- 6 Magneto-optical Readout
- 7 Effects of High-numerical-aperture Focusing on the State of Polarization
- 8 Computer Modeling of the Optical Path
- 9 Noise in Magneto-optical Readout
- 10 Modulation Coding and Error Correction
- 11 Thermal Aspects of Magneto-optical Recording
- 12 Fundamentals of Magnetism and Magnetic Materials
- 13 Magnetostatics of Thin-film Magneto-optical Media
- 14 Mean-field Analysis of Amorphous Rare Earth–Transition Metal Alloys
- 15 Magnetization Dynamics
- 16 Origins of Coercivity
- 17 The Process of Thermomagnetic Recording
- 18 Media Characterization
- References
- Index
Summary
Introduction
The process of magnetization reversal in thin magnetic films is of considerable importance in erasable optical data storage. The success of thermomagnetic recording and erasure depends on the reliable and repeatable reversal of magnetization in micron-sized areas within the storage medium. A major factor usually encountered in descriptions of the thermomagnetic write and erase processes is the coercivity of the magnetic material. Technically, the coercivity Hc is defined for a hysteresis loop as the value of the applied field at which the net magnetization becomes zero. Coercivity, however, is an ill-defined concept which may be useful in the phenomenology of bulk reversal, but its relevance to the phenomena occuring on the spatial and temporal scales of thermomagnetic recording must be seriously questioned. To begin with, there is the problem of distinguishing the nucleation coercivity from the coercivity of wall motion. Then there is the question of speed and uniformity of motion as the wall expands beyond the site of its origination. Finally one must address issues of stability and erasability, which are intimately related to coercivity, in a framework wide enough to allow the consideration of local instabilities and partial erasure. It is fair to say that the existing theories of coercivity are generally incapable of handling the problems associated with thermomagnetic recording and erasure. In our view, the natural vehicle for conducting theoretical investigations in this area is computer simulation based on the fundamental equations of micromagnetics, the basis for which was laid down in the preceding chapter.
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- The Physical Principles of Magneto-optical Recording , pp. 586 - 637Publisher: Cambridge University PressPrint publication year: 1995