ABSTRACT

Designs using thin metallic layers, based on either giant magnetoresistive effect [1, 2] or tunneling magnetoresistance [3], have already found application in hard drive read heads, in magnetic random access memories, and in magnetic field sensors (see Chapter 5, Volume 1, and Chapter 14, Volume 3). These designs employ a magnetoresistive spin-valve effect: The current passing through them depends on the magnetization configuration 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. Despite 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 field generates a magnetic soliton that carries information through the network. The logic output is then encoded in the resulting magnetic configuration. Similar proposals have used either domain walls to propagate information or shape anisotropy [5, 6]. A different all-metallic magneto-logic paradigm relies on magnetic tunneling junctions as building blocks [7–9]. The output of a logic operation is decoded from the current amplitude flowing through a combination of these junctions. Similarly to the case of magnetic random access memories, the logic operands are encoded using multiple bit (current) lines. This in turn changes the resistance of the junction, and the added effect from various junctions denotes an output of a logic operation.