ABSTRACT
Spin-torques have been quantitatively measured from the ferromagnetic resonance excited by them. The spins of the injected electrons interact with the local spin-angular momentum, S→2, in the free layer by exchange interaction and exert torque. The spectrum excited by the spin-transfer torque exhibits a single bell-shaped peak, whereas that excited by the field-like torque is of a dispersion type. In a magnetic recording system such as a hard disk drive, data retention is guaranteed based on the probabilistic magnetization reversal model with a thermal activation process. Since the magneto-resistance effect in magnetic tunnel junctions (MTJ) is large, the thermal fluctuation in the magnetization in MTJs produces considerable electric noise under a dc bias. A large injection may result not only in magnetization switching but also in a continuous precession of magnetization. This spin-transfer oscillation was first observed in current perpendicular to plane- giant magnetoresistance nanopillars and nanocontacts.
