Study On The Bias Effect Of Tunneling Magnetoresistance Of The Magnetic Tunnel Junctions With Single-Crystal Barrier

In the field of spintronics research,magnetic tunnel junctions are an important class of physical devices.Due to the presence of disordered scattering,the magnetic tunnel junctions based on amorphous Al-O barrier exhibit low tunneling magnetoresistance?TMR?and can not meet the requirements of the next generation of spintronic devices.Therefore,the magnetic tunnel junctions with single-crystal Mg O barrier has gradually become a research hotspot.It is found that the Mg O-based magnetic tunnel junctions have many physical effects that are very different from Al-O barrier junctions.Among them,the bias effect has been extensively studied.The experimental results show that the TMR of the single-crystal Mg O-based magnetic tunnel junctions have non-monotonic characteristic with the change of the bias voltage,which can not be explained by the traditional magnetic tunnel junctions theoretical model.To this end,this paper introduces the diffractive physics method to account for the periodicity of the single-crystal barrier layer and the influence of the coherence,and constructs a theoretical model of the magnetic tunnel junctions of the single-crystal barrier layer,and the bias effect of the single-crystal barrier layer magnetic tunnel junctions tunneling magnetoresistance is calculated using the theoretical model.The main research results are as follows:1.For the case of ordinary ferromagnetic electrodes,the study found that parallel conductance G_P?parallel conductance?,antiparallel conductance G_AP?antiparallel conductance?and TMR all oscillate with bias,and the physical mechanism comes from the periodic potential of the single-crystal barrier to tunnel Coherent diffraction of electrons.By calculating the variation curves of G_P,G_AP,and TMR with bias voltage under different the half of the exchange splitting?,chemical potential?,and barrier layer scattering potential component v?K_h?,in this paper,the effects of ferromagnetic electrodes and barrier layer materials on the bias effect are studied.Theoretical calculation results show that:G_P,G_AP,and TMR all increase monotonically with the?bias oscillation cycle,and monotonically decrease with v?K_h?;G_Pmonotonously increase with the chemical potential?;The amplitudes of G_Pand G_APoscillations with bias voltage increase monotonically with the chemical potential?.2.For the case of ordinary ferromagnetic electrodes,the theoretical calculation results show that the bias voltage in the range of 0 to 100 m V will not significantly change the characteristics of G_P,G_AP,and TMR oscillating with barrier thickness.However,when the bias voltage is increased to8 V,the amplitude and frequency of G_P,G_AP,and TMR oscillating with the barrier thickness are significantly reduced.In addition,due to the splitting of the energy band of the ferromagnetic electrode,the DC component of G_APwill decrease significantly as the bias voltage increases,while the DC component of G_Pwill remain basically the same as the bias voltage increases.3.By introducing the effect of lattice distortion,the effect of bias voltage on the temperature effect in the case of ordinary ferromagnetic electrodes is studied.Theoretical calculation results show that the small bias in the range of 0 to 100 m V has almost no effect on TMR.In this bias voltage range,TMR decreases monotonously with temperature,and the change in TMR mainly comes from the change in G_APwith temperature.The above results are consistent with the experimental results of Mg O-based magnetic tunnel junctions.When the bias voltage is increased to1 V,G_Pand G_APare non-monotonic with temperature.When the bias voltage is further increased to8 V,G_P,G_AP,and TMR are basically unchanged with temperature.In addition,the period and amplitude of G_APwith the bias oscillation both decrease with increasing temperature.4.In the case of half-metallic ferromagnetic electrodes,the behavior of G_APwith bias voltage is essentially different from that of ordinary ferromagnetic electrodes,that is,G_APincreases monotonically with the bias voltage without oscillating with the bias voltage.Physically,G_APdoes not oscillate with bias voltage as explained below:For the case of half-metallic ferromagnetic electrodes,the scattered wave vectors p_<sub><sup>zand q_<sub><sup>zcorresponding to all incident tunneling electron wave vectors can only be an imaginary number,so the scattered electrons p_<sub><sup>zand q_<sub><sup>zpartial wave function are decaying rather than oscillating.The G_APmonotonically increases with the bias voltage because:for the G_??channel,the contributing tunneling electrons and the empty states available for tunneling electron transitions increase simultaneously with the increase of the bias voltage.In addition,the bias effect of G_Pand TMR are similar to those of ordinary ferromagnetic electrodes.