Magnetic noise in MgO-based magnetic tunnel junction rings

摘要

Magnetization switching is investigated in ring-shaped MgO-based magnetic tunnel junctions with 168% tunneling magnetoresistance. Besides the forward and reverse onion states, two vortex states and several metastable states are observed for the ferromagnetic free layer. Electrical noise is used to characterize the low frequency magnetization dynamics; a stationary 1/f noise spectrum is observed within each magnetic state but they are separated by noise peaks which show a 1/f~2 spectrum that is associated with slow random telegraph fluctuations. In the 1/f region, the normalized magnetic noise parameter, α_(mag), is shown to be consistent with the fluctuation-dissipation theorem.