The Study Of The Spin-dependent Electronic Transport Properties In The Nanostructures

The spin-dependent electronic transport properties are investigated in the nanostructures. The effect of the applied bias on the spin-dependent transport properties in the magnetic nanostructures, the effect of the delta-doping on the spin-dependent transport of an electron in the nanostructures, the bias-and temperature-dependent magnetoresistance effect in the magnetic nanostructures, and the effect of the spin-orbit coupling on the spin-dependent resonant tunneling in the non-magnetic nanostructures are in detail studied. The contents and achievements are as follows:1. The spin-dependent transport properties of the electron in the magnetic nanostructures modulated by the applied biasThe spin-dependent transport properties of the electron in the magnetic nanostructures modulated by the applied bias are theoretically studied, (a) The spin-dependent electron transport is in detail studied in a nanostructure under an applied bias and two parallel-magnetic barriers. The numerical results show that the large spin polarization can be achieved in such a device, and the degree of electron-spin polarization strongly depends on the applied bias, (b) The bias-and temperature-dependent electron transport is in detail studied in a nanostructure modulated by the applied bias and four magnetic barriers. The results show that the large spin polarization also can be achieved in such a nanostructure, and the degree of the spin polarization obviously increases with increasing applied bias. They also show that the conductance curves for the different temperatures obviously intersect at the same Fermi energy for the low Fermi energy, and the degree of spin-polarization decreases with the increase of temperature. Thus, we can control the electron transport through changing the bias and temperature. These interesting properties may be helpful for making the bias-tunable spin filters. 2. The spin-dependent transport properties of an electron in the magnetic nanostructures with the delta-doppingThe effect of the delta-dopping on the electronic transport properties is investigated in the magnetic nanostructures. (a) The spin-dependent electronic transport properties are studied in the magnetic nanostructures with the delta-dopping and two magnetic fields that can be expressed in delta-function profile. The results show that, the large spin polarization can be achieved in such a device, and the degree of the spin polarization strongly depends on the height of the delta-function potential. The results also show that the conductance polarization apparently has the bigger oscillatory magnitudes with the height of delta-function potential increasing. (b) The effect of the delta-dopping on the electronic transport properties is studied in a magnetic nanostructure with four magnetic fields that can be expressed in delta-function profile. It is found that the transmission probability and the electron conductance are dramatically suppressed by the weight of the delta-dopping. However, the spin-injection efficiencies are obviously enhanced. In addition, the transmission probability and the spin polarization both show a periodic profile with the increase of the distance between the two middle magnetic fields, (c) The electronic transport properties are investigated in a nanostructure modulated by the periodic magnetic barriers and delta-dopping. The numerical results show that the electron transport properties strongly depend on the number of periods. For the number of periods m>1, the spin splitting occurs in each resonant domain, and the number of the spin-splitting peaks in each resonant domain is m-1. These interesting features are helpful for developing new types of spintronic devices.3. The electronic transport properties and temperature-dependent magnetoresistance effect in a magnetic nanostructureThe temperature-dependent magnetoresistance effect is investigated in two magnetically modulated nanostructures. The first one can be experimentally realized by depositing two parallel ferromagnetic strips on the top and bottom of a two-dimensional electron gas, where the distance between the two ferromagnetic strips is L, and a suitable external magnetic field can change the relative orientation of the two magnetizations. When the relative orientation of the two magnetizations is parallel, the structure is parallel alignment, while the structure is antiparallel one when the relative orientation of the two magnetizations is antiparallel. Applying a bias voltage across the two-dimensional electron gas induces the triangular electrical potential. The second one also can be realized by depositing two parallel ferromagnetic strips on the top and bottom of a two-dimensional electron gas. However, the position of the two ferromagnetic strips in the two nanostructures is obviously different from each other, and no bias is applied on this nano structure. From the numerical calculations, we find that a considerable magnetoresistance effect can be achieved due to the quite distinct conductance difference for electrons through the antiparallel and parallel magnetization configurations. We also find that the magnetoresistance effect obviously depends on the temperature and the applied bias as well as the position of the two ferromagnetic strips, thus may leading to bias-and temperature-tunable magnetoresistance devices.4. The effect of the spin-orbit interaction on the electronic-resonant tunneling in the non-magnetic nanostructuresThe effect of the spin-orbit coupling interactions on the spin-dependent electronic transport properties is investigated in a non-magnetic nanostructure, which is asymmetrical double barriers of strained heterostructure or periodic nanostructure, and no external magnetic field is applied on this nanostructure. The origin of the spin of electrons is the two types of the spin-orbit couplings:(a) Dresselhaus spin-orbit coupling, which is due to the inversion asymmetry of the bulk material (b) Rashba spin-orbit coupling which is due to heteropotential asymmetry (where the two-dimensional electron gas is in the plane.). Detailed numerical results tell us that:(1) in the asymmetrical double barriers of strained heterostructure, the large spin polarization can be achieved due to the effect of Rashba and Dresselhaus spin-orbit couplings, and both the transmission probability and the spin polarization show a periodic profile with the increase of the well width; (2) in the nonmagnetic three barriers of strained heterostructure, the large spin polarization can be achieved in such a structure mainly due to the Rashba spin-orbit term induced splitting of the resonant level, and the spin polarization strongly depends on the well width and the thickness of the middle barrier as well as the height of the middle barrier; (3) in the periodic non-magnetic nanostructure, the electron transport properties significantly depend on the number of periods, and a large spin polarization can be achieved, we also find that for m>1, the resonant splitting occurs in the transmission curves of spin-up and spin-down electrons, in each resonant region there are 2m-1 resonant peaks, and the splitting rule is different from that obtained in the periodic magnetic nanostructure.