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In recent years,resistive switching(RS)effect has attracted considerable attention due to its scientific interest and important applications [1-3].It has been emphasized that a robust and predictive understanding of its underlying mechanisms is essential for applications [4].Although extensive research efforts have been made,the mechanisms for this effect are still elusive.NiO is a model system for the resistive switching effect and the formation/rupture of Ni filaments is considered to be essential [5].However,a direct and robust evidence of their presence is still lacking.Moreover,it is not clear whether a single filament or multiple filaments are involved in the low and high resistance states,and how the filament or filaments evolve in the RESET process.Since Ni filaments should be ferromagnetic,magnetic measurement may provide some useful information on Ni filaments.Moreover,the magnetoresistance(MR)for different resistance states ofNiO RS sample,which has not been addressed before,is another interesting issue and helpful for the understanding of the behavior related to Ni filaments.We studied the RS effect of NiO thin films grown on Pt/Ti/SiO2/Si substrates.A direct observation of Ni filaments in NiO with RS effect was realized by using transmission electron microscopy.Current-voltage measurement,alternating current impedance spectroscopy,magnetization and MR measurements suggest a multifilamentary picture for the process of filament rupture during the RESET process.Theoretical calculation reveals the role of oxygen vacancies in the evolution of Ni filaments.The observations of different magnetizations and MR characteristics for the LRS and HRS shed light on the evolution of Ni filaments.These results also provide an opportunity to tune the resistance of the devices both magnetically and electrically,as well as to tune the magnetism of the devices electrically,which are important for applications in multifunctional devices.