Spintronics
SPINTRONICS: AN INTRODUCTION
INTRODUCTION:
From the earliest transistor to the remarkably powerful microprocessers, most electronic devices have employed circuits that express data as binary digits, or bits: ones and zeroes represented by the existence or absence of electric charge. Furthermore, the communication between microelectronic devices occursby the binary flow of electric charges.The technologies that emerged from this simple logic have created a multitrillion dollar per year global industry whose products are ubiquitous. Indeed,the relentless growth of microelectronics is often popularly summarized in Moore’s Law, which holds that microprocessors will double in power every 18 months as electronic devices shrink and more logic is packed into every chip.Yet even Moore’s Law will run out of momentum one day as the size of individual bits approaches the dimension of atoms; this has been called the end of the silicon road map. For this reason and also to enhance the multifunctionality of devices (for example, carrying out processing and data storage on the same chip), investigators have been eager to exploit another property of the electron—a characteristic known as spin. Spin is a purely quantum phenomenon roughly akin to the spinning of a child’s top or the directional behavior of a compass needle. The top could spin in the clockwise or counterclockwise direction; electrons have spin of a sort in which their compass needles can point either “up” or “down” in relation to a magnetic field. Spin therefore lends itself elegantly to a new kind of binary logic of ones and zeros. The movement of spin, like the flow of charge, can also carry information among devices. One advantage of spin over charge is that spin can be easily manipulated by externally applied magnetic fields, a property already in use in magnetic storage technology. Another more subtle (but potentially significant) property of spin is its long coherence, or
INTRODUCTION:
From the earliest transistor to the remarkably powerful microprocessers, most electronic devices have employed circuits that express data as binary digits, or bits: ones and zeroes represented by the existence or absence of electric charge. Furthermore, the communication between microelectronic devices occursby the binary flow of electric charges.The technologies that emerged from this simple logic have created a multitrillion dollar per year global industry whose products are ubiquitous. Indeed,the relentless growth of microelectronics is often popularly summarized in Moore’s Law, which holds that microprocessors will double in power every 18 months as electronic devices shrink and more logic is packed into every chip.Yet even Moore’s Law will run out of momentum one day as the size of individual bits approaches the dimension of atoms; this has been called the end of the silicon road map. For this reason and also to enhance the multifunctionality of devices (for example, carrying out processing and data storage on the same chip), investigators have been eager to exploit another property of the electron—a characteristic known as spin. Spin is a purely quantum phenomenon roughly akin to the spinning of a child’s top or the directional behavior of a compass needle. The top could spin in the clockwise or counterclockwise direction; electrons have spin of a sort in which their compass needles can point either “up” or “down” in relation to a magnetic field. Spin therefore lends itself elegantly to a new kind of binary logic of ones and zeros. The movement of spin, like the flow of charge, can also carry information among devices. One advantage of spin over charge is that spin can be easily manipulated by externally applied magnetic fields, a property already in use in magnetic storage technology. Another more subtle (but potentially significant) property of spin is its long coherence, or