Stress in Spin-Valve Nanopillars due to Spin Transfer

We report a mechanical effect in spin-valve nanopillars due to spin transfer. A polarized current carrying electron spins transfers torque to local magnetization and leads to a magnetic switching of free layer. Like classical Einstein-de Haas effect, the conservation of angular momentum needs the free layer to offset the change of angular momentum and then a mechanical rotation occurs. The free layer is not free standing, so the mechanical angular momentum will be revealed as stress and strain. We study the effect of a spin induced stress in a nanopillar device with in-plane magnetization. Our calculations show that the tress in as device is dependent on frequency and the ratio of length/thickness and about 1 MPa at GHz. It is concluded that the stress owing to spin transfer is much less than the internal stress of film and does not introduce damage to the device.