ABSTRACT
Designs using thin metallic layers, based on either giant magnetoresistive e¥ect [1,2] or tunneling magnetoresistance [3], have already found application in hard-drive read heads, in magnetic random access memories and magnetic ¢eld sensors (see Chapters 6 and 36). žese designs employ a magnetoresistive spin-valve e¥ect: že current passing through them depends on the magnetization con¢guration of two terminals. Over the last two decades, the advances in magnetic storage have enabled a 1000-fold increase in the capacity of computer hard drives using metal-based spin valves. In spite of this remarkable success, there are only a few seminal attempts to propose logic gates in all-metallic magnetic systems. Cowburn and Welland [4] have implemented a room temperature magnetic quantum cellular automata network of submicrometer magnetic dots interacting via magnetostatic interactions. To trigger a logic operation, an applied oscillating magnetic ¢eld generates a magnetic soliton that carries information through the network. že logic output is then encoded in the resulting magnetic con¢guration. Similar proposals have used either domain walls to propagate information or shape anisotropy [5,6]. A di¥erent all-metallic magneto-logic paradigm relies on magnetic tunneling junctions as building blocks [7-9]. že output of a logic operation is decoded from the current amplitude ¦owing through a combination of these junctions. Similar to the case of magnetic random access memories, the logic operands are encoded using multiple bit (current) lines. žis in turn changes the resistance of the junction, and the added e¥ect from various junctions denotes an output of a logic operation.
