All computers rely on electric currents to process information. Magnetic materials are generally used for storage applications. Now two researchers at Cambridge University in the UK have shown how to perform logic operations with a network of interacting submicron-sized magnetic dots. Moreover, the network works at room temperature. Russell Cowburn and Mark Welland claim that such a magnetic microchip could outperform current microelectronic technology by several orders of magnitude (Science 287 1466).
The number of transistors on a silicon chip has doubled every 18 months, but many observers believe that semiconductor technology will reach its limit in a decade or so. This has prompted the development of new devices, including so-called quantum cellular automata (QCA). So far, however, QCA based on semiconductors have only been operated at very low temperatures. Cowburn and Welland have taken a different approach to QCA and used magnetic metals rather than semiconductors.
Each QCA network consists of a single elongated input dot followed by a chain of 69 circular dots. The dots were 110 nanometres wide, 10 nanometres thick and their centres were about 135 nanometres apart. They were fabricated in Supermalloy, a common magnetic alloy, with electron-beam lithography. The logical state of each dot is given by the direction of its magnetization (which can point in one of two directions), and the dots interact through magnetostatic interactions. An applied oscillating magnetic field provides energy for the system and acts as a clock.
