Structural Design And Property Investigation On Multi-resistive States Of Tunnel Junctions

Recently, with the developments of science of materials and technology of thin film preparation, multi-resistive-states tunnel junctions have attracted increasing attention due to their advantages of application in memories, switchable devices and spintronic devices. The main points of how to design novel multi-resistive-states tunnel junctions using multifunctional material to increase the tunnel resistive states, the interfacial effect on the properties of tunnel junctions, the influence of applied stress, bias voltage and magnetoelectric coupling on the properties of tunnel junctions are the hot topics in the research of this field.This paper focuses on three parts. The model of sixteen resistive state of tunnel junction with polarized ferromagnetic, ferroelectric material is designed firstly. Then the influence of interfacial magnetoelectric coupling on the properties of tunnel junction is investigated in ferromagnetic-ferroelectric-ferromagnetic tunnel junction. In the end, the influence of applied bias voltage on the properties of tunnel junction is studied. The main points and results are shown as follows:1. Choosing the ferromagnetic-ferroelectric composite films as tunnel barrier and ferromagnetic material with different Thomas-Fermi screening lengths as the electrodes, tunnel junction with sixteen resistive states is designed. Calculations show that choosing proper parameters, the multi-resistive-states tunnel junction could present sixteen distinguishable tunnel resistive states.2. The influence of interfacial magnetoelectric coupling on multi-resistive-states tunnel junction with different electrodes in Thomas-Fermi screening lengths is studied in ferromagnetic-ferroelectric-ferromagnetic tunnel junction. The results show that the ferroelectric polarization, the ferroelectric permittivity of tunnel barrier, the Thomas-Fermi screening lengths of the electrodes, magnetic exchange splitting energy are key factors effecting the magnetoelectric coupling.3. The influence of applied bias voltage on the property of multi-resistive-states tunnel junction with different Thomas-Fermi screening lengths in the electrodes is investigated in ferromagnetic-ferroelectric-ferromagnetic tunnel junction. The results show that the effect of applied bias voltage could safely neglect when the permittivity of ferroelectric barrier is independent of electric field. However, considering the permittivity of ferroelectric barrier depending on the electric field, the applied bias voltage could have a strong influence on the properties of tunnel junction, which partly agrees with the experimental results.