He cautions that these numbers are theoretical at this point. Whether or not the design will actually work depends on the materials used in the sensor stack. The materials that have the right magnetic and electric properties are complex alloys, such as lead zirconium titanate, cobalt iron vanadium, and platinum manganese. So far, only micrometers-thick layers of these materials have been shown to have the necessary magnetic and electric properties.
To make a practical read head, the layers in the sensor stack will have to be two to three nanometers thick. It’s not clear if the materials will retain their properties at those dimensions. “When you go to such small thicknesses … the behavior can change tremendously,” says MIT physicist Jagadeesh Moodera, one of the discoverers of the tunnel magneto-resistance effect used in current read heads.
Moreover, putting together the complex alloys in a few-nanometers-thick sensor could be a challenge. The materials all have different properties, and they don’t necessarily agree with each other, Moodera says. For example, one material might be sensitive to oxygen, while another requires oxygen. Nevertheless, the idea is sound, he says, and “it makes sense to pursue it [experimentally].”
Vopsaroiu agrees that his design will have to meet many challenges. But the read-head sensors used today are just as complicated, and manufacturers have developed ways to produce them easily. Besides, he says, to reach the milestone of one-terabit-per-square-inch disk density, the industry will have to experiment with newer reading technologies.