Effects of Resistance States on the Magnetoresistance in Ni/Al2O3/Ni by Resistive Switching

Formation and rupture of conductive filaments is one of the main mechanisms for unipolar resistive switching (URS), which can be manifested by the observation of magnetoresistance (MR) effect if ferromagnetic metallic filaments are formed. In this work, ferromagnetic metallic Ni is used as top and bottom electrodes on Al2O3 film, and stable URS behavior is observed after a forming process. By inserting a series resistor in the circuit during the set process, the resistance value at low resistance state (LRS) increases with increasing resistance of the series resistor. The URS behavior can be attributed to the formation and rupture of metallic Ni filaments penetrating through the thin Al2O3 layer, which has been confirmed by the observation of tunneling magnetoresistance. However, the MR value decreases continuously with increasing resistance in LRS, which is due to that the diameter of Ni conductive filaments becomes smaller. Thus, the nonmagnetic scattering at the surfaces of filaments increases, leading to the decrease of MR.