In a normal semiconductor, an electron’s spin is arranged randomly; one points this way, one points that. But when a majority of electrons have the same spin, the result is a magnetic field. That means any computer chip in which the spins are controlled can function as a nonvolatile memory, because spin stays the same until an external force acts to change it. Because the memory is nonvolatile, meaning it doesn’t require a flow of current to keep refreshing the information, it uses far less electrical power, allowing batteries to last longer and reducing their chance of overheating. It also allows a transistor to use both charge and spin and function as both a logic gate and a memory. A computer chip could perform all the same tasks with fewer circuits, leaving room to add additional circuits without having to make the devices even smaller.
Spintronic devices already exist; hard drives store much more information than a decade ago, because Moodera and others developed spintronics-based read heads that can detect tiny changes in magnetism, allowing more-plentiful and smaller chunks of data to be packed into the same space. And one company has started selling magnetic random-access memory, another spin-based technology, that doesn’t require a flow of current to store data.
But to apply spintronics to logic circuits, scientists have to figure out how to put the spin they want into the transistor and how to detect it on the other side once the circuit has manipulated it. They want a thin film they can place on top of the semiconductor and in which they can use the magnetic field to align the spin of the electrons, before transporting those aligned electrons into the semiconductor. Moodera’s indium oxide is a potential candidate for such a film, once he fully understands it and can figure out how to optimize it.Moodera is unwilling to predict how long it will take to build a practical spintronic circuit, though he estimates that thousands of scientists in the United States, Asia, and Europe are working on it: “It could be 10 years, it could be six. It’s difficult to say.” But he points to how spintronics have improved hard drives from capacities of a few megabytes 15 years ago, when no one had even thought of using spintronics, to current iPods that let you carry a 60-gigabyte drive around in your pocket. “I’m an optimistic researcher,” he says.