Current induced oscillation of a single magnetic domain wall

Direct observation of the dynamics of a single domain wall (DW) in a NiFe-Cu nanowire is investigated. This reveals that such a topological particle indeed has a very small but finite mass of 6.6/spl times/10/sup -23/ kg, and interacts with high-frequency ac electric currents by exchanging momentum. This measurement is made possible by observing resonance of a single DW in which DW motion induced by a oscillating electric current in a tunable potential is used. The dominant mechanisms in these nanowires arise from the exchange coupling between the local magnetization and the spin of conduction electrons. The first mechanism is due to the reflection of conduction electrons by the DW, called momentum transfer. The other is the transfer of the spin angular momentum from conduction electrons to the DW as the electrons pass through the DW. This spin-transfer effect is proportional to the spin polarization of the current.