Zihua Wu

Temperature dependence of current-voltage characteristics of Ag–La0.7Ca0.3MnO3–Pt heterostructures

Temperature dependence of the current-voltage characteristics of Ag–La0.7Ca0.3MnO3–Pt heterostructures was investigated and the related current conduction mechanism was discussed. Poole-Frenkel emission and trap-controlled space charge limited current mechanisms are employed to explain the carrier transport at low and high temperature regions, respectively. Obvious hysteresis is observed only in the region dominated by space charge limited current with traps exponentially distributed in energy. This can be explained by the retention behavior of trapped carriers at the Ag∕La0.7Ca0.3MnO3 interface layer. It is proposed that the resistance switching can be optimized for device application by the electrode/film interface defect engineering.

Asymmetric fatigue and its endurance improvement in resistance switching of Ag -La0.7Ca0.3MnO3 -Pt heterostructures

The asymmetric fatigue behaviour of electric-pulse-induced resistance switching, that is, only switching from a low to a high resistance state, exhibits obvious fatigue behaviour and has been investigated in Ag–La0.7Ca0.3MnO3–Pt heterostructures. This asymmetric fatigue is strongly dependent on the applied electric-pulse voltage and can be refreshed by applying a voltage sweep in vacuum condition (<100 Pa). The fatigue and its refreshment are related to the increase and decrease in threshold voltage in the resistance switching, respectively. The results indicate that fatigue endurance in resistance switching of Ag–La0.7 Ca0.3MnO3–Pt heterostructures can be improved through the operation of environmental oxygen pressure.

Reversible multilevel resistance switching of Ag-La0.7Ca0.3MnO3-Pt heterostructures

The electric-pulse–induced resistance switching of the Ag–La 0.7 Ca 03 MnO 3 (LCMO)–Pt heterostructures was studied. The multilevel resistance switching (MLRS), in which several resistance states can be obtained, was observed in the switching from high to low resistance state (HRS → LRS) by applying electric pulse with various pulse voltages. The threshold pulse voltages of MLRS are related to the initial resistance values as well as the switching directions. On the other hand, the resistance switching behavior from low to high resistance states (LRS → HRS) shows unobvious MLRS. According to the resistance switching behavior in serial and parallel modes, MLRS was explained by the parallel effect of multifilament forming/rupture in the Ag–LCMO interface layer. The present results suggest a possible application of Ag–LCMO–Pt heterostructures as multilevel memory devices.

Reversible change in magnetic moment and specific heat of La0.9Ca0.1MnO3 at different resistance states

The magnetic moment and the specific heat of La0.9Ca0.1MnO3 (LCMO) at different resistance states induced by electric pulses were studied. It was found that the magnetic moment and the specific heat increase with decreasing resistance, and these changes are reversible. The reversible change in specific heat was shown to be attributed mainly to the ferromagnetic-spin-waves component by fitting specific heat. These results indicated that the electric pulses modulated the magnetic configuration of LCMO at low temperature, which would result in a large variation in magnetization and specific heat associated with ferromagnetic spin waves.

Resistance and magnetization of La0.7Ca0.3MnO3 bulk at different resistance states induced by electric pulses

Electric-pulse-induced resistance (EPIR) switching behaviour was observed in bulk La0.7Ca0.3MnO3 polycrystalline. Temperature dependences of resistance and magnetic moment at different resistance states were studied. The metal–insulator phase transition temperature changed with the resistance states, which suggested that the EPIR phenomenon is related to the modulating bulk properties of perovskite manganites. The Curie temperature derived from the magnetic moment measurement did not change with the resistance states, which implied that there was no ferromagnetic–metal and antiferromagnetic–insulator transition occurring in perovskite manganite global materials. These results provided a new evidence for a filamentary mechanism in the EPIR effect.