Theoretical Study On Tunneling Magnetoresistance Of Magnetic Tunnel Junction With Single Crystal Barrier Based On Half-metallic Ferromagnetic Electrodes

Spintronics is a subject that designs electronic devices by regulating the spin of electrons.As a spintronic device with a huge potential of application,magnetic tunnel junction?MTJ?is an important research object of spintronics.The tunneling magnetoresistance?TMR?is one of the important indicators to evaluate the performance of MTJ.The greater the TMR,the higher the sensitivity of the MTJ.Due to disordered scattering is weakened significantly,MTJ with single-crystal Mg O barrier can obtain higher TMR than that with amorphous Al-O barrier.On the other hand,half-metallic ferromagnets,whose spin polarizability is 100%,can achieve high TMR.Therefore,a lot of research efforts have been made to study the MTJs based on single-crystal Mg O barrier and half-metallic ferromagnetic electrodes experimentally,and the existing experimental results can not be explained by traditional theoretical models.To this end,this paper establishes a theoretical model based on a single-crystal barrier and half-metallic electrodes by introducing an optical method,and physical effects such as thickness and temperature are calculated by using the model.The main results are as follows:1.Based on the diffraction physics,a theoretical model for the MTJs with single-crystal barrier is developed by us.Within it,the single-crystal barrier is treated as a periodic diffraction grating.Therefore,when the tunneling electrons pass through the barrier,coherent diffraction will occur,which will bring strong coherence to the out-going electrons.That is to say,the transmitted wave function contains multiple partial waves with different wave vectors.Physically,it is equivalent to forming multiple scattering channels with different energy.The theoretical result shows that,the conductance of the antiparallel channel G_??is not zero even if the electrodes are half-metallic ferromagnets when v?K _h??29??35?+?.Accordingly,the TMR will be limited.For the MTJs with half-metallic ferromagnetic electrodes,which explains the contradiction between the theoretical results of the traditional model and the exising experimental results.2.Effects of thickness on the Mg O-based MTJs of half-metallic ferromagnetic electrodes are studied.The theoretical results show that:the parallel conductance?G_P?and TMR do not oscillate with the thichness of barrier when v?K _h??29??35?+?,G_P and TMR oscillate with the thichness of barrier when v?K _h??27??35?+?;whether v?K _h??29??35?+?or v?K _h??27??35?+?,the antiparallel conductance(G_AP)does not oscillate with the thichness of barrier.Since the tunneling electrons are scattered by the periodic potential field of single-crystal barrier,the wave function of the electrons is coherent,which makesG_P and TMR oscillate with the thichness of barrier.Because wave vectors of the tunneling electrons in the antiparallel channel are imaginary,so the wave function of the electrons is no longer coherent,G_AP dose not oscillate with the thichness of barrier.3.The effects of the chemical potential?,half the exchange splitting?35?of the half-metallic electrodes and the component of the scattering potential of the barrier v?K _h?on the thickness effect are studied in this paper.The theoretical results show that:the period and amplitude ofG_Pand TMR increase monotonically with the chemical potential?and half the exchange splitting?35?,and decrease monotonically with v?K _h?;the curve ofG_AP with thickness of the barrier moves up with the chemical potential?and v?K _h?,and moves down with half the exchange splitting?35?.Physically,changes in the period and amplitude ofG_P and TMR are caused by changes in the coherent wave vectors,while the reason the why the curve ofG_AP shifts is that the number of tunneling electrons in the antiparallel channel changes.4.In this paper,effects of temperature on Mg O-based MTJs based on half-metallic ferromagnetic electrodes are studied by introducing the influence of lattice distortion.The theoretical results show that:G_P and TMR oscillate with temperature when v?K _h??27??35?+?,G_Pand TMR do not oscillate with temperature when v?K _h??29??35?+?,whether v?K _h??29??35?+?or v?K _h??27??35?+?,G_AP does not oscillate with temperature.Similar to the oscillation in the effects of thickness,the oscillation ofG_P and TMR with temperature comes from the coherent of tunneling electrons.G_AP increases monotonically with temperature because the higher the temperature,the more tunneling electrons contribute to the conductance.In addition,the effects of strainK_h??₀,defect concentration?and covery temperature _cT on the temperature effect are studied.The theoretical results show that:when the strainK_h??₀ or the defect concentration?becomes larger,G_P and TMR become more sensitive of to temperature;when the covery temperature _cT becomes smaller,G_P and TMR become more sensitive to temperature.These results come from the modulation of v?K _h?by strain,defect concentration and covery temperature.5.The effect of temperature on the thickness effect is studied in this paper.The theoretical results show that:due to the temperature brings the modification of v?K _h?,the oscillating period and amplitude ofG_P with the thickness of barrier are modulated by the temperature,while the curve ofG_AP with the thickness of barrier moves up with the temperature.