Study On Polarization And Tunneling Magnetoresistance About Double Tunnel Junctions

The electron is a quantum mechanical object which,apart from charge,also has a spin. Devices and integrated circuits based on electronic charges and their transportation have been widely used in the world.The properties of the electrons and holes enrichment the transport characters of semiconductor materials.The central theme here is the use of spin degrees of freedom in solid-state systems.In order to utilize the spin degrees of freedom in solids, particularly in semiconductors the current electronics is based on,we need to fabricate appropriate materials,understand the spin-dependent phenomena,andcontrol the spins.The discovery of GMR(giant magnetoresistance) and TMR(tunneling magnetoresistance) in metallic spin valves have revolutionized applications such as magnetic recording and memory, and launched the new field of spin electronics-'spintronics',which is centered on electron spin including their generation,transport and detection.Latest some researches indicate similar properties between spin degree of freedom and electronic charge.Some examples are spin Hall effect,spin field-effect transisitor and spin current generated in magnetic and nonmagentic semiconductors.These phenomena originate from spin-orbit coupling of materials.Spin-orbit coupling will not only open a new universe for spintronics,but also guide the way to theoretical and experimental investigations of spintronic devices.In this paper,we investigate the transmission,polarization,and tunneling magnetoresistance of the ferromagnet/insulator/semiconductor/insulator/ferromagnet double tunnel junction in the presence of the Dresselhaus spin-orbit coupling interaction and an electric field.Due to the thin oxide layers at the interfaces between the ferromagnet and the semiconductor caused by the experimental preparation technique,the thickness of the insulators between the ferromagnet and the semiconductor should be considered theoretically. We consider the difference of electron effective masses in three different material regions and the intrinsic conductivity mismatch between ferromagnetic metal and semiconductors.Our treatment still relies on the free-electron model of the conduction electrons to study the spin-polarized transport properties through the junction.This model is relatively simple and has been adopted with success to study the spin-polarized tunneling between iron-group ferromagnetic metals and the tunneling through ferromagnet/semiconductor(insulator)/ferromagnet junctions.Using a transfer-matrix method and the Airy function,we calculate the transmission, polarization and tunneling magnetoresistance(TMR) of the double-barrier structure subjected to an electric field and Dresselhaus spin-orbit coupling.The obtained results indicate that(â…°) the polarization can be enhanced by reducing the insulator layers at zero temperature,and(â…±) the tunneling magnetoresistance inversion can be illustrated by the infuence of the Dresselhaus spin-orbit coupling effect in the double-barrier structure.Due to the Dresselhaus spin-orbit coupling effect,the tunneling magnetoresistance inversion occurs when the energy of a localized state in the barrier matches the Fermi energy E_f of the ferromagnetic electrodes.We hope our results can stimulate interest in experimental efforts in designing spin-polarized resonant tunneling devices.