Magnetic Interactions and Spin Transport

Stuart Wolf This book originated as a series of lectures that were given as part of a Summer School on Spintronics in the end of August, 1998 at Lake Tahoe, Nevada. It has taken some time to get these lectures in a form suitable for this book and so the process has been an iterative one to provide current information on the topics that are covered. There are some topics that have developed in the intervening years and we have tried to at least alert the readers to them in the Introduction where a rather complete set of references is provided to the current state of the art. The field of magnetism, once thought to be dead or dying, has seen a remarkable rebirth in the last decade and promises to get even more important as we enter the new millennium. This rebirth is due to some very new insight into how the spin degree of freedom of both electrons and nucleons can play a role in a new type of electronics that utilizes the spin in addition to or in place of the charge. For this new field to mature and prosper, it is important that students and postdoctoral fellows have access to the appropriate literature that can give them a sound basis in the funda­ mentals of this new field and I hope that this book is a very good start in this direction.

1. Electron Spins in Ionic Molecular Structures.- 1.1. Introduction.- 1.2. Magnetic Cations.- 1.3. Cation Sites in Anion Lattices.- 1.4. Electron Energy Levels in Crystal Fields.- 1.5. Magnetocrystalline Anisotropy.- 1.6. Spin Exchange Between Cations.- 1.7. Spin Ordering in Ferrimagnetic Oxides.- 1.8. Spin Transport in Oxides.- References.- 2. Secondary Magnetic Properties.- 2.1. Introduction.- 2.2. Magneto-Optic Properties.- 2.3. The Kubo Formula.- 2.4. Ab Initio Calculations of the Kerr Effect.- 2.5. Magneto-Crystalline Anisotropy.- 2.6. First-Principle Calculations.- Appendix A.- Appendix B.- References.- 3. Spin-Dependent Transport in Magnetic Multilayers.- 3.1. Introduction.- 3.2. Kubo-Greenwood Formula for Conductivity.- 3.3. Free Electrons with Random Point Scatterers.- 3.4. Boltzmann Equation.- 3.5. Landauer Formula for Conductance.- 3.6. Spin-Dependent Tunneling.- References.- 4. Magnetotransport (Experimental).- 4.1. Introduction and Overview.- 4.2. Electronic Transport in F-Metals and F-Based Alloys.- 4.3. Spin-Dependent Tunneling and “Polarization”.- 4.4. Spin-Injection Studies.- 4.5. Giant Magnetoresistance in F/N Multilayers and Granular Alloys.- 4.6. Granular Magnetoresistance.- 4.7. Tunneling Magnetoresistance.- 4.8. Colossal MR.- 4.9. Miscellaneous Phenomena.- References.- 5. Magnetic Characterization of Materials.- 5.1. Introduction.- 5.2. Units.- 5.3. Magnetic Moment, Magnetization, and Susceptibility.- 5.4. Diamagnetism and Paramagnetism.- 5.5. Magnetic Ordering.- 5.6. Magnetometry.- 5.7. Magnetic Characterizations through Hyperfine Interactions.- 5.8. Concluding Remarks.- 6. Magnetic Domain Imaging of Spintronic Devices.- 6.1. Introduction.- 6.2. Scanning Electron Microscopy with Polarization Analysis.- 6.3. Magnetic Force Microscopy.- 6.4.Magneto-Optic Imaging.- 6.5. Transmission Electron Microscopy.- 6.6. Magnetic Imaging with X-Ray Dichroism.- 6.7. Conclusions.- References.- 7. Domain Dynamics and Magnetic Noise.- 7.1. Introduction.- 7.2. Overview of Magnetic Noise in Device Applications.- 7.3. Magnetic Domains and Magnetization Reversal.- 7.4. Electrical Noise.- 7.5. From Magnetic Fluctuations to Electrical Noise.- 7.6. Stabilization of Magnetic Sensors.- 7.7. Media Noise in Magnetic Recording.- References.- 8. Deposition Techniques for Magnetic Thin Films and Multilayers.- 8.1. Introduction.- 8.2. Thermal Evaporation.- 8.3. Sputtering.- 8.4. Pulsed Laser Deposition.- 8.5. Film Thickness Measurement and Control Techniques.- 8.6. Characterization Techniques.- 8.7. Summary.- References.- 9. Magnetic Sensors.- 9.1. Introduction.- 9.2. Why We Sense Magnetic Fields.- 9.3. Magnetic Sensing Technologies.- 9.4. Spin-Dependent Magnetoresistive Materials.- 9.5. Magnetoresistive Sensor Design.- 9.6. Anisotropic Magnetoresistive Sensors.- 9.7. Giant Magnetoresistive Sensor Design.- 9.8. Spin-Dependent Tunneling Sensor Design.- 9.9. Conclusions.- References.- 10. High Speed Magnetoresistive Memories.- 10.1. Introduction.- 10.2. Memory Fundamentals.- 10.3. Plated Wire and Planar Film Memories, Precursors.- 10.4. Magnetoresistive Memory Design Factors.- 10.5. Honeywell’s Original MRAM.- 10.6. Pseudo Spin Valve, Giant Magnetoresistive Memories.- 10.7. Memories with Spin Valve Materials.- 10.8. Spin Dependent Tunneling Memory Cells.- 10.9. Summary.- References.- 11. Hybrid Devices.- 11.1. Introduction.- 11.2. Hybrid Ferromagnet-Superconducting Devices.- 11.3. Hybrid Ferromagnet-Semiconductor Devices.- References.