Hard/soft magnetic tunnel junction device with stable hard ferromagnetic layer

摘要

A magnetic tunnel junction (MTJ) of the type using soft (low magnetic coercivity) and hard (high magnetic coercivity) ferromagnetic layers separated by an insulating tunnel barrier (a hard/soft MTJ device) is stable without loss of magnetization after repeated cycling of its magnetic state. The MTJ device is based on the discovery that the mechanism of demagnetization in a hard/soft MTJ device is via coupling of the hard ferromagnetic layer to the soft ferromagnetic layer via the formation and motion of domain walls in the soft ferromagnetic layer. The MTJ device includes adjacent ferromagnetic structures that provide a transverse biasing magnetic field to the soft ferromagnetic layer. The transverse biasing field permits coherent rotation of the magnetic moment of the soft ferromagnetic layer without the formation of magnetic domains when suitable switching fields are applied. The elimination of the effect of domain walls in the soft ferromagnetic layer can also be achieved by an MTJ device with the soft ferromagnetic layer having a larger surface area than the hard ferromagnetic layer so that any domain walls are concentrated at the edges of the soft ferromagnetic layer and thus have minimal effect on the hard ferromagnetic layer.