The Spin-dependent Transport And Optoelectronic Properties Of The 6,6,12-graphyne-based Magnetic Tunnel Junction Devices

With the wide application of electronic devices in daily life,people's demand for them has gradually increased,and their functions are required more diversification.As the traditional electronic devices have reached the physical limit,scientists turn their attention to nano-spin electronic devices.In the initial application of electronic devices,only the charge was regarded as a carrier of information transmission and storage,while the spin properties were totally ignored by researchers.In 1988,giant magnetoresistance effect was discovered by scientists,opening up a new era of spintronic devices development.Electronic spin has great advantages in terms of information storage,energy consumption,and implementation of logic functions.Therefore,the research of spintronic devices is favored by people.In order to achieve high density of spintronic devices,attention has been paid to constructing spintronic devices using nano-sized materials.Nano-spin electronic devices have many advantages,such as small size,fast operation,low power consumption,large information storage and non-volatile.Among many materials,carbon allotropes have become popular research objects.Graphene has motivated great interest recently,because of its unique physical and chemical properties,e.g.the Dirac cone in the energy band structure.The Dirac cone exists not only in graphene but also in a new two-dimensional carbon allotrope called graphyne,in which 6,6,12-graphyne has two different Dirac cones.The unit cell of 6,6,12-graphyne is rectangular,and there are different properties in two different directions of rectangle.Its electrical properties are excellent,and its mobility is much larger than that of graphene.Hence,we choose graphene nanoribbons as electrodes and6,6,12-graphyne nanodot as the central scattering region to construct devices,and study the quantum transport properties of the devices.In the first chapter,we mainly introduce the related contents of giant magnetoresistance,the advantages of nano-spin electronic devices,and the two materials selected in the construction of the device,namely graphene and graphyne.In the second chapter,we briefly introduce the calculation methods used in the study,including all kinds of approximate treatments used in the calculation,and computing software,namely,ATK and Nanodcal.In the third chapter,the construction of the 6,6,12-graphyne-based magnetic tunnel junction devices and the spin-dependent transport properties are introduced.In the fourth chapter,the related optoelectronic properties of the 6,6,12-graphyne-based magnetic tunnel junction devices are introduced.In the fifth chapter,we summarize the research content of this article and look forward to the further work of the 6,6,12-graphyne-based magnetic tunnel junction devices.The research of spin-dependent transport properties has shown that magnetic tunnel junction devices have prominent tunneling magnetoresistance effect and the tunneling magnetoresistance values are as high as 10~5%.Besides,they also exhibit spin-filtering effect.More importantly,a new method to generate spin-filtering effect is applied in the research process,namely controlling magnetism to achieved spin-filtering effect.The research of optoelectronic properties has shown that magnetic tunnel junction devices can generate spin-polarized photocurrents at low energy and high energy,but their mechanism is different.In addition,the spin-polarized photocurrents are dependent on the magnetization directions of the electrodes and the polarization direction of light,but are nearly independent on the polarization form of light.More interestingly,if the magnetization directions of the two electrodes are antiparallel,the two light-generated spins flow in opposite direction.This provides a new method for obtaining spin current.