Current-induced multiple spin structures in 100 nm ring magnetic tunnel junctions

Nanoring magnetic tunnel junctions (NR-MTJs) with outer diameters as small as 100 nm and a thin wall width of 25 nm have been fabricated. NR-MTJs acquire different resistance states when they are switched by electrical currents compared with when they are switched by external magnetic fields. This can be explained by combining the effects of spin-transfer torque and circulatory Oersted field during current-induced switching. We provide a model for computing the equivalent circulatory magnetic field due to the nonadiabatic spin torque of the spin-polarized current through the MTJ. The multiple spin states in nanoring MTJs provide prospects for magnetic memory devices.