Angular dependence of magnetoresistance during magnetization reversal on magnetic tunnel junction ring

Microstructured magnetic tunnel junction ring with outer/inner diameter of 2/1 μm has been fabricated to investigate the angular dependence of magnetoresistance during magnetization reversal process. The minor loop of magnetoresistive curve reveals four distinct resistance levels associated with four magnetization configurations within the free layer throughout the magnetization reversal. The magnetoresistance decreases with increasing angle between applied external field and biasing direction, which is resulted from the relative alignment of total magnetization of pinned and free layer. An extra feature appeared in the minor loop when the external field is transverse to the biasing direction; this can be attributed to a vortex-pair formation/ annihilation in the free layer. Furthermore, a series of schemes of magnetic configurations of pinned and free layers are illustrated to explain the routes of minor loops.