Effects of current on nanoscale ring-shaped magnetic tunnel junctions
  We report the observation and micromagnetic analysis of current-driven magnetization switching in nanoscale ring-shaped magnetic tunnel junctions. When the electric current density exceeds a critical value of the order of $6\times 10^{6}$A/cm$^2$, the magnetization of the two magnetic rings can be switched back and forth between parallel and antiparallel onion states. Theoretical analysis and micromagnetic simulation show that the dominant mechanism for the observed current-driven switching is the spin torque rather than the current-induced circular Oersted field. 
Hong-Xiang Wei, Jiexuan He, Zhen-Chao Wen, Xiu-Feng Han, Wen-Shan   Zhan, and Shufeng Zhang