Theoretical Study On The Temperature-Bias Phase Diagram Of MgO-based Magnetic Tunnel Junctions

MgO-based magnetic tunnel junction is a hot issue in the field of spin electronic devices.And its TMR will change significantly with the applied bias and temperature.Therefore,in practical applications,it is necessary to optimize the applied bias and temperature to achieve the maximum TMR,which is equivalent to finding the maximum phase point of TMR in the temperature-bias phase diagram of MgO-based magnetic tunneling junction.For this reason,this paper develops a theory which is suitable for magnetic tunnel junctions with single crystal barrier.Within the theory,the single crystal barrier is regarded as a periodic grating,and the tunneling process is treated by optical diffraction theory,so the coherence of the tunneling electron can be well taken into account.Based on this theory,temperature-bias phase diagram of MgO-based magnetic tunnel junctions is calculated.The research results are as follows :1.In this thesis,the bias effect and temperature effect of MgO-based magnetic tunnel junction under the condition of ordinary ferromagnetic electrodes are studied,and the tunneling conductance and TMR under different barrier layer periodic potential,half the exchange splitting energy and chemical potential are calculated respectively.The calculation results show that under different barrier layer periodic potential,half the exchange splitting energy and chemical potential,the tunneling conductance and TMR oscillate with bias voltage and temperature.In physics,this is due to the coherence caused by the scattering of barrier layer periodic potential during electron tunneling.In addition,the period and amplitude of tunneling conductance and TMR with bias and temperature oscillation are modulated by the periodic potential of the barrier layer,half the exchange splitting energy of the ferromagnetic electrode and the chemical potential.2.In this thesis,the temperature-biased TMR phase diagrams of MgO-based magnetic tunnel junctions with different barrier layer periodic potential,ferromagnetic electrode half the exchange splitting energy and chemical potential are calculated.The theoretical results show that the temperature-biased TMR phase diagram depends significantly on the barrier periodic potential.At the same time,it is found that the maximum phase point of TMR can be located in the room temperature region by adjusting the half the exchange splitting energy.In addition,the bias voltage corresponding to the maximum phase point of TMR can be changed by adjusting the chemical potential.The above results show that the temperature and bias characteristics of MgO-based magnetic tunnel junction can be optimized by adjusting the half the exchange splitting energy,the chemical potential and the periodic potential of the barrier layer,which is beneficial to the practical application of MgO-based magnetic tunnel junction.3.In this thesis,the bias effect and temperature effect of MgO-based magnetic tunnel junction under the half-metallic ferromagnetic electrodes are studied,and the tunneling conductance and TMR under different barrier layer periodic potential,half the exchange splitting energy and chemical potential are calculated.The calculation results show that the antiparallel conductance increases monotonically with temperature and bias voltage.This is due to the half-metallic nature of the ferromagnetic electrode,which leads to the attenuation of 50 % of the partial wave of the tunneling electron,and thus destroys the coherence between the tunneling partial wave and the oscillation of the transmission coefficient.In addition,the increase in temperature contributes to the realization of the electronic transition in the anti-parallel channel.The higher the bias voltage is,the greater the difference in the chemical potential of the ferromagnetic electrodes on both sides is,and the more electrons contribute to tunneling in the antiparallel channel.Both of them will lead to the increase of the antiparallel conductance.The characteristics of parallel conductance and TMR with bias and temperature oscillation are similar to those of common ferromagnetic electrode magnetic tunnel junction.4.In this thesis,the temperature-biased TMR phase diagrams of MgO-based magnetic tunnel junctions with half-metallic ferromagnetic electrodes under different barrier layer periodic potential,half the exchange splitting energy of ferromagnetic electrodes and chemical potential are calculated.The theoretical results show that the temperature-bias TMR phase diagram of the magnetic tunnel junction with half-metallic ferromagnetic electrodes is also sensitive to the periodic potential of the barrier layer.In addition,in the range of the parameters selected in this paper,the maximum TMR phase point of the half-metallic ferromagnetic electrode magnetic tunnel junction is in the low bias region,and the maximum TMR phase point can be in the room temperature region by adjusting the half the exchange splitting energy and the chemical potential of the ferromagnetic electrode.It can be seen from the above that the half-metallic ferromagnetic electrode MgO-based magnetic tunnel junction is more in line with the actual application requirements than the ordinary ferromagnetic electrode MgO-based magnetic tunnel junction.