Electric-field control of strain-mediated magnetoelectric random access memory

A strain-mediated magnetoelectric random access memory with electric-field-writing is presented, which consists of a magnetic tunnel junction (MTJ) in intimate contact with a ferroelectric (FE) layer. The calculations show that the magnetization vector in the free layer of the MTJ unit can switch in-plane by 90°upon applying an appropriate electric field to the FE layer, as compared to the common 180°reversal induced by magnetic field or spin-current. A perfect interface between the FE layer and the MTJ is assumed. The free layers used for illustration include either (001)-oriented or polycrystalline magnetic films of Fe-Co alloy, CoFe₂ O₄ (CFO), Ni, and Fe₃ O₄. Among them, the (001)-oriented FeCo and CFO films with positive magnetocrystalline anisotropy constant (i.e., K₁ >0) show an abrupt magnetization switching, while a gradual magnetization switching takes place in the (001)-oriented Ni and Fe₃ O₄ films with K₁ <0 as well as the polycrystalline films. Such electric-field-induced in-plane magnetization switching can result in a remarkable change in the MTJ's electric resistance. In particular, hysteretic dependence of the device resistance on the applied electric field is obtained for the cases of the (001)-oriented FeCo and CFO free layers that exhibit the abrupt magnetization switching, whereby a nonvolatile information storage process can be achieved. The influence of the shape of the free layer on both magnetization and resistance switching features is discussed.