Shot Noise In The Magnetic Tunnel Junction With External Electric Field, Interface Impurities And The Effective Mass

As early as in the seventies, we have begun to study the spin-polarized tunneling in order to get spin-dependent electronic states of information. In recent years, spin-polarized tunneling through ferromagnetic / insulator / ferromagnetic has received increasing attentions. In this article, we use the scattering method to study the characteristics of shot noise in magnetic tunnel junction with external electric field, interface impurities and effective quality.(1) We first study the tunneling probability and shot noise of ferromagnetic / insulator / ferromagnetic junction, ferromagnetic / insulator / ferromagnetic / insulator / ferromagnetic junction at the external electric field. We first calculate the tunneling probability and shot noise of the ferromagnetic / insulator / ferromagnetic junction as a function of the electronic Fermi energy for different values of the applied bias, we found that all resonant spectra of shot noise are split into doublets in the peak value of the tunneling probability, this is easy to know from S = (e³V_a)/(2Ï€h)T(E)( 1 -T( E)),the split peak of shot noise does not become obviously in the first peak value of the tunneling probability in smaller energy, the split peak of shot noise become clearly with the increase of the energy. As the bias is increased, the peak of the tunneling probability is observed with smaller energy,and the values of the peaks become smaller,but the split peak of shot noise is observed with smaller energy,the value becomes bigger. Then we calculate tunneling probability and shot noise of ferromagnetic / insulator / ferromagnetic / insulator / ferromagnetic junction as a function of the electronic Fermi energy for different values of applied bias when the two outside potential wells are spin-up and the middle potential well takes spin-up or spin-down respectively, we find that the peak value of the tunneling probability correspond with the split peak of noise, with the increase of the bias voltage, the peak value of tunneling probability need smaller energy, while the occurance of split peak value of noise corresponds with smaller energy. The split peak of shot noise becomes clearly with the increase of energy .When the electrons of the middle potential well are spin down, the peak value of tunneling probability and shot noise need smaller energy compared with the previous figure, but the split peak of shot noise becomes less obviously, the peak becomes more sharply. The distance between the first and the second peak becomes smaller.(2)We finally study the tunneling probability and noise in the existence of interface impurities and the effective mass of ferromagnetic / normal metal / ferromagnetic junction. We first calculate the noise without considering the impact of electron effective mass as a function of impurity potentialγfor different electronic Fermi energy, we find that the noise is not zero when the angleθ=Ï€,it indicates that the spin-value effect is not ideal here ,because in the ferromagnetic layer,the electrons are not polarized entirely, there are also some spin-down electrons in the Fermi surfaces, there is small current when the polarization direction of the two ferromagnetic layer is opposite, it is close to the actual conditions; We then calculate the noise as a function of the electronic Fermi energy for different impurity potentialγ, we find that when the impurity potentialγis zero, the oscillation of shot noise is axisymmetric, it can be explained well with the use of a two-band model, with the increase of the impurity potentialγ, the oscillation of shot noise becomes anti-symmetric, and the number of the peaks increases, this is due to impurity-induced quasi-bound states. When the Fermi energy is big, the inverse symmetry is weakened,it indicates that the difference resulted from spin-dependent becomes smaller with the increase of Fermi energy. As the angle increases, the peak corresponding with the same Fermi energy becomes more sharply, the noise is not zero when the angleθ=Ï€,it indicates that the spin-value effect is not ideal here ,the reason is as above.We have also studied the noise when the interface impurities and the effective mass act on the ferromagnetic / normal metal / ferromagnetic junction at the same time, we first calculated the noise as a function of impurity potentialγwhen the interface impurities and the effective mass act on the ferromagnetic / normal metal / ferromagnetic junction at the same time, we discover that the wave vector is improved when we change the effective mass of electrons, thereby, the place of the resonant peak alters. the impurity potentialγcorresponding to suppressed shot noise becomes smaller. It indicates that the effective mass of electrons has an effect on shot noise. We then calculate the noise as a function of the electronic Fermi energy impurity potentialγfor different impurity potentialγ, we find that when m1 is different with m3 ,shot noise is anti-symmetric when the impurity potentialγis zero , when the Fermi energy is bigger, the inverse symmetry is weakened; when m₁ = m₃=1,shot noise is symmetric when the impurity potentialγis zero ,with the increase ofγ, shot noise becomes anti-symmetric, when the Fermi energy is bigger, the inverse symmetry is weakened. It is noteworthy that the oscillation of the noise is always the greatest when m₁ m₃=1 or m₁ = m₃≠1. the waveform considering the impact of the effective mass changes smaller than that without considering the impact of the effective mass , and the peaks become more pronounced.