When a spin-polarized current passes from a ferromagnet into a non-magnetic material, the spins of the itinerant electrons are 'flipped' at the interface between the two materials, producing a mechanical torque. Pritiraj Mohanty and co-workers have now made a nanoscale torsion oscillator that can measure this torque in a metal nanowire with unprecedented sensitivity. The oscillator is made of silicon and the metal nanowire runs from top left to bottom right in the scanning electron micrograph on the cover. The left half of this wire is a 50-nm-thick layer of cobalt (which is ferromagnetic) and the right half is a 50-nm-thick layer of gold (which is not magnetic). This highly sensitive approach to measuring torque could have applications in spintronics and fundamental physics, chemistry and biology.
Cover design by Karen Moore
Letter p720; News & Views p710