| Spintronics originated from the discovery of the giant magnetoresistance effect,and is mainly devoted to the study of spin-polarized transport properties of electrons and the design and development of new spin-related microelectronics devices.Compared with traditional silicon-based electronics devices,spintronics devices using electronic spin as the signal carrier have the advantages of low energy consumption,high circuit integration and fast data processing speed.Spin caloritronics is the combination and extension of traditional thermoelectronics and spintronics,which can be used to solve the problems of heat dissipation and waste heat recovery due to the miniaturization and extremely high operating speed of devices.With the increasing demand for functional devices with green,non-toxic and low energy consumption,low-dimensional carbon-based organic magnets have entered people’s limelight,especially the graphene and graphene-like materials.In this thesis,the combination of density functional theory and non-equilibrium Green’s function is used to study the electronic structure and magnetic properties of the graphene nanoribbons co-doped with boron and nitrogen（8-ZGNR-H（N,B））and the graphite-like carbon nitride（g-C4N3）,and the thermal and electrical spin transport properties and magnetoresistance effect of the two-electrode devices based on above materials,and the main results obtained are as follows.（1）We designed a two-electrode homojunction based on graphene nanoribbons co-doped with boron and nitrogen and investigated its thermal spin transport property.The calculation results of the electromagnetic stability and electronic structure of the electrode show that the 8-ZGNR-H（N,B）nanoribbons in the antiferromagnetic ground state exhibit perfect half-metallicity,i.e.,the conductive electrons are in only one spin direction.The spin current calculation results show that the spin filtering effect,the spin Seebeck effect,and the single-spin negative differential thermal resistance effect are observed in the device.When an external local magnetic field is used to transform the device from the parallel ground state to the anti-parallel magnetized state,the system exhibits a sign-reversal giant magnetoresistance effect,and the magnetoresistance at room temperature can be maintained at around 105%.（2）We further constructed and designed the 8-ZGNR-H（N,B）/8-ZGNR-H heterojunction two-electrode device.The system is in the[AFM-AFM]ground state when no magnetic field is applied and in the[FM-AFM],[AFM-FM]and[FM-FM]magnetized states when a magnetic field is applied.The thermal transport properties of this heterojunction device are highly dependent on the magnetic state it is in,and the thermally-induced currents can be controlled by modulating the magnetic structure,resulting in a sign-reversed giant magnetoresistance effect.Compared with the homojunction,the heterojunction system exhibits more excellent transport behaviors when it is in a different magnetic state.In the[AFM-AFM]magnetic state,the heterojunction exhibits thermally-induced spin Seebeck effect and spin diode effect with a certain threshold temperature,temperature switching effect,and negative differential thermal resistance effect;the spin Seebeck effect and the spin diode effect are also found in the[FM-AFM]magnetic state;a perfect spin filtering effect is shown in the[AFM-FM]magnetic state;and the spin-Seebeck effect with larger spin current values is produced in the[FM-FM]magnetic state.The heterojunction system has potential application prospects in the development of multifunctional thermal spintronics devices.（3）We also designed two kinds of two-dimensional devices（Zigzag-type and Armchair-type）based on monolayer g-C4N3 with different transmission directions,and investigated the thermal and electrical spin transport properties of these two devices.The results of the thermal transport study show that both Zigzag-type and Armchair-type devices have good low-temperature spin filtering effects and thermally-induced negative differential resistance effects.Differently,the Zigzag-type device also exhibits spin-crossover action.When the magnetic structure of the two types of devices is changed from the parallel ground state to the anti-parallel magnetized state,the maximum thermal magnetoresistance can reach about105%,and it can also be maintained at 2 orders of magnitude at room temperature.The results of the electrical transport study show that both Zigzag-and Armchair-type devices have also the electrically-induced spin filtering effect,while the Armchair-type device has also the voltage-controlled spin switching behavior and the negative differential resistance effect. |
