Study On The Manipulation Of Magnetization And Photovoltaic Effect With Resistive Switching Effect In BiFeO₃-based Materials

Due to their multiferroic properties and multi-field coupling effects,multiferroic materials have attracted people's interest for a long time,especially their application in novel multifunctional devices,such as memories,sensors and spintronic devices.In recent years,there has been the surge of interest in some other physical properties of multiferroic materials,such as the resistive switching effect,ferroelectric photovoltaic effect and so on.The coupling of these properties can bring us a brand new avenue to achieve multi-field modulation and design novel multifunctional devices.We choose the BiFeO3-based material to demonstrate our idea,we studied the variation of the magnetization and photovoltaic effect during the resistive switching process.The main contents and results are presented as follows.In this work,a remarkable modulation of magnetization with resistive switching effect in the BiFe0.9Mn0.1O3 thin films was achieved.We prepare polycrystalline BiFe0.9Mn0.1O3 thin films on Pt/Ti/SiO2 wafers by a sol-gel process.The film exhibits typical unipolar resistive switching effect.Moreover,remarkable magnetization variation with different resistance was observed,i.e.,the film shows high saturation magnetization with low resistance,while showing low saturation magnetization at high resistance state,such variation of magnetization can reach as high as?40%.Further study shows that the magnetization variation with different resistance states is repeatable and has a good retention.By analyzing the XPS measurements,we found the conversion of Fe ion balance state between Fe2+ and Fe3+ during resistance switching process,which is the main cause of the magnetization variation.The further first-principle calculations showed that the doping of Mn into the BiFeO3 could induce an impurity energy level and it could also make the conversion of Fe ion valence state more facilely.Based on the conductive filament model,we proposed a possible mechanism of tuning the magnetization during resistive switching process:the magnetization variation is dominated by the conversion of Fe ion valence state,which is accompanied with the formation and rapture of the conduction filaments during the resistive switching process.This work provides us a promising avenue to design multistate devices.On the other hand,the modulation of photovoltaic effect with resistive switching effect in polycrystalline BiFeO3 thin films is realized.we prepare polycrystalline BiFeO3 thin films on ITO wafers by a sol-gel process.We found that the film exhibits typical bipolar resistive switching effect,and a remarkable variation of photovoltaic effect at different resistance states was observed,the open-circuit voltage at low resistance state is small,while the open-circuit voltage at high resistance state is larger.We further proposed a possible explanation on such behaviors,during the resistive switching process,the forming of conductive path can break down the inner electric filed,which could affect the separation and combination of carriers,so it may cause the different ferroelectric photovoltaic effect with different resistances.This work also provides us a possible way to design novel multistate memory devices.