Study On The Bias Voltage Effect Of Magnetic Tunnel Junction With Single Crystal 2D-material Barrier

Magnetic tunneling junction(MTJ),as an important spintronic device,is widely used in data storage and other aspects.With the increasing demand for storage capacity,people put forward new requirements for the size and performance of magnetic tunnel junctions.The 2D-material with atomic layer thickness possesses many novel physical properties,which will help reduce the size of the magnetic tunnel junction and improve their performance.Therefore,the magnetic tunneling junction with single crystal 2D-material barrier has been widely studied.It is found that the tunneling magnetoresistance oscillates with the applied bias voltage in the magnetic tunneling junction of single crystal 2D-material barrier.This bias characteristic can not be explained by traditional theoretical model.In this paper,based on the optical method,a theoretical model for the magnetic tunnel junction with single crystal 2D-material barrier was developed.The theoretical model regards the single crystal barrier layer as a periodic grating,so the periodicity of the2D-material barrier and its coherence can be fully taken into account.Furthermore,using this theoretical model,this paper calculates respectively two cases:one is the MTJ with normal ferromagnetic electrode,the other is the MTJ with half-metallic ferromagnetic electrode.The main theoretical results are as follows:1.The bias characteristics of tunneling conductance and TMR under the condition of ordinary ferromagnetic electrode and the influence of ordinary ferromagnetic electrode parameters on the bias characteristics are studied.Theoretical calculations show that:the parallel tunneling conductanceG_P,anti-parallel tunneling conductanceG_AP and TMR oscillate with the bias voltage due to the coherent scattering of tunneling electrons by the barrier layer of two-dimensional single crystal materials.The amplitude of TMR oscillates with the bias voltage increases monotonically with the half of the exchange splitting?_ex,and decreases monotonically with the chemical potential?.In addition,bias has little effect on the selection of ferromagnetic electrode materials,that is,under different bias,ferromagnetic electrode materials with low chemical potential?and high half of the exchange splitting?_ex should be selected to achieve high TMR.2.The effects of the barrier layer parameters of the two-dimensional material on the bias voltage effect and the effect of bias voltage on the thickness oscillation of the barrier layer under the condition of ordinary ferromagnetic electrodes are studied respectively.The results show that:the periods of_PG,G_AP,and TMR oscillation with bias voltage decrease monotonically with the barrier thickness and the Fourier component v(K_h)of scattering potential.In addition,when the bias voltage is lower than 0.1 V,the bias voltage has little effect on the thickness variation curve of tunneling conductance.When the bias voltage continues to increase,the thickness variation curve of the anti-parallel tunneling conductanceG_AP will be significantly dependent on the bias voltage.3.The bias characteristics of tunneling conductance and TMR under the condition of half-metallic ferromagnetic electrode and the influence of half-metallic ferromagnetic electrode parameters on the bias characteristics are studied.The results show that:unlike the case of ordinary ferromagnetic electrodes,since the complete spin polarization destroys the coherence of the tunneling electron wave,G_AP no longer oscillates with the bias voltage,but monotonically increases with the bias voltage.Similar to the case of ordinary ferromagnetic electrodes,G_P and TMR oscillate with bias voltage,and the change rate of the bias characteristic curve of TMR in the low bias region monotonically increases with the half of the exchange splitting?_ex,and monotonically decreases with the chemical potential?.In addition,the selection of half-metallic ferromagnetic electrode materials under bias voltage is similar to that of ordinary ferromagnetic electrode.4.The effects of two-dimensional material barrier layer parameters on the bias voltage effect and the effect of bias voltage on the thickness oscillation of barrier layer under the condition of half-metallic ferromagnetic electrode are studied respectively.The results shows that:the period of G_P and TMR oscillation with bias decreases monotonically with the barrier thickness and the Fourier component v(K_h)of scattering potential,while the bias characteristics ofG_AP are almost unaffected by the barrier thickness.In addition,forG_P and TMR,the influence of bias voltage on the thickness oscillation effect is similar to that of the ordinary ferromagnetic electrode,and the thickness variation curve ofG_AP will shift downward as the bias voltage increases.