chapter  3
38 Pages

Chapter 3

Abstract ................................................................................. 80 3.1 Introduction .................................................................. 81 3.2 Ion Beam Interaction Processes ................................. 81

3.2.1 Ion Energy Deposition ...................................... 81 3.3 Ion Irradiation Effects in Permalloy Films ................ 83 3.4 Ion Implantation to Modify Film Composition .......... 87 3.5 Modification of Anisotropy and Coercivity ................. 89

3.5.1 Co/Pt Multilayers .............................................. 89 3.5.2 Chemically Ordered FePt ................................. 92 3.5.3 Ballistic Displacement Model ........................... 93

3.5.3.1 Ion-Induced Disorder ........................... 93 3.5.4 Comparison with Experimental Data .............. 95 3.5.5 Enhancement Mechanisms ............................... 96 3.5.6 Other Systems ................................................... 98

3.6 Modification of Magnetization .................................... 98 3.7 Magnetoresistance and Remanent Magnetization

Ratio .............................................................................. 99

3.8 Potential Applications in Magnetic Disk Storage Technology .................................................................. 100 3.8.1 Fundamental Resolution Issues for Ion Beam

Processing ........................................................ 102 3.8.2 Recording Media .............................................. 105

3.8.2.1 Projection Ion Beams ........................ 105 3.8.2.2 Soft Bit in Hard Matrix .................... 107 3.8.3.3 Nanoparticle Islands ......................... 108

3.8.3 Track-Width Definition of GMR Sensors ...... 110 3.8.4 Track Width for Magnetic Write Heads ........ 110

3.9 Concluding Remark ................................................... 111 References ............................................................................ 112

ABSTRACT

The physical and technological consequences of ion implantation and ion irradiation in semiconductors, structural metals and polymers have been studied in depth over the past 30 years. However, only in relatively recent times have we started to explore the remarkable interactions and opportunities for new technologies resulting from ion beam treatment of magnetic materials. This chapter reviews the basic processes of ion beam interactions in solids, and proceeds to explore the role of these processes in customtailoring the magnetic properties (e.g., moment, coercivity, anisotropy, magnetoresistance) of thin film magnetic materials, such as permalloy or CoPtCr, having special relevance to applications in magnetic information storage and the development of advanced disk and head structures for highdensity disk drives. The mechanism of ion beam modification of anisotropy and coercivity in multi-layer Co-Pt or Fe-Pt thin film media for perpendicular recording is explored in depth. High spatial resolution (tens of nanometers) obtained with ion irradiation using stencil masks and/or projection ion beam tools enables robust, cost-effective full-disk patterning of storage media at densities exceeding 100 Gb/in2. The extension of this technique to patterned self-assembled FePt nanoparticle media is dem-

onstrated. Finally, we display the application of ion beam patterning in fabricating GMR read and write heads characterized by uniquely narrow track width performance.