Applied physics: Addressing an antiferromagnetic memory

Spintronics (1) is one of the most commercially successful nanotechnologies. The invention of the giant-magnetoresistance spin valve (2) revolutionized the magnetic recording industry, enabling the immensely cheap, high-density disk drive storage on which the data centers that support our insatiable demand for cloud computing, social networking, and video sharing technologies rely. The combination of magnetic tunneling junctions (3) and spin-transfer torque (STT) (4) has brought about the prospect of magnetic random-access memory (MRAM), written using STT, as a way to provide nonvolatile storage that can be written and operated using extremely low power. Such technologies have just entered the marketplace. Even more energy-efficient writing is possible using the recently discovered spin-orbit torque (SOT) (5). All of these technologies use ferromagnets—the type of magnetic materials that “stick to the fridge” because they possess a magnetic moment—to store the data; the direction of that magnetic moment (“north” or “south”) represents the 0 or 1 of a digital bit. In both STT and SOT, the flow of a spin-polarized electrical current exerts torques on the magnetic moments to affect the change in magnetization direction that writes this bit. On page 587 of this issue, Wadley et al. (6) show that a hitherto exotic class of magnetic materials, antiferromagnets, are candidates for an entirely new type of spintronic memory.