Research On The Magnetism And Thermal Spin Transport Of Novel Low-Dimensional Structures

The utilization of electron spins as information carriers in spin electronic devices could lead to faster speeds,lower energy consumption,and higher integration density than traditional charge-based electronic devices,which has promoted the booming development of spintronics.The generation of spin currents is one of the most important issues in spintronics.The unique electronic structures of magnetic materials allow for the generation of spin-polarized carriers,making them crucial in the generation of spin currents.Using thermal spin transport effects such as the spin Seebeck effect of magnetic materials can produce spin currents efficiently.In recent years,a multitude of new two-dimensional materials have emerged that exhibit outstanding spin properties,making them an ideal platform for spintronic devices.Therefore,exploring and controlling the spin-related properties of novel low-dimensional structures is of extraordinary significance.This paper focus on several novel two-dimensional materials,e.g.,Cr I₃,graphether,and vanadium dichalcogenides,and their derivative structures.Based on density functional theory combined with the non-equilibrium Green’s function,the magnetism,electronic structures,and thermal spin transport of these systems are investigated,the underlying physical mechanisms are analyzed,and the manipulation approaches are explored.The main research contents in this paper are as follows.（1）The interlayer magnetic coupling of anti-parallel stacked bilayer Cr I₃ is studied.Two magnetic phases determined by the stacking order are revealed,and the electronic structures of the two magnetic phases are calculated.Based on the calculations of differential charge density,the different interlayer magnetic coupling mechanisms of the two magnetic phases are analyzed and explained using the superexchange magnetism theory.And the controlling of strain and electronic doping on the interlayer magnetism is further explored.This work could provide theoretical support for the design of heterojunctions and spintronic devices based on two-dimensional magnetic materials.（2）The electronic structures of armchair-edged and zigzag-edged nanoribbons based on graphether,a novel two-dimensional material,are investigated.It is found that the armchair-edged graphether nanoribbons are non-magnetic semiconductors.Symmetry plays a key role in their band structures,which could trigger an indirect-direct transition of the bandgap,following the odd-even parity of the nanoribbon.While the zigzag-edged graphether nanoribbons are ferromagnetic and could be used to generate completely spin-polarized currents.The study of graphether nanoribbons will facilitate the energy band engineering for related materials and the design of spin valve devices.（3）By constructing edge defects,spin caloritronic devices based on magnetic graphether nanoribbons are designed.These devices exhibit a robust spin Seebeck effect and can generate pure spin currents under a temperature gradient.The underlying physical mechanism could be attributed to the symmetrical spin-resolved transmission spectra.It is further confirmed that magnetic graphether thermal spintronic devices possess excellent spin thermoelectric performance,including a high spin Seebeck coefficient and a huge spin figure of merit.This work proposes a new material platform for producing pure spin currents by the spin Seebeck effect,and also provides theoretical guidance for the design of spin thermoelectric devices based on low-dimensional structures.（4）The monolayers of three vanadium dichalcogenides with intrinsic magnetism are investigated.The anisotropy in spin transport of all three structures is found.Based on these structures,armchair and zigzag spin thermoelectric devices are constructed,and their thermal spin transport is studied.It is demonstrated that all six devices can generate fully spin-polarized currents,and the mechanisms behind their different thermal spin transport properties are discussed.The thermal spin conversion capabilities of these devices are also explored and compared.The results suggest that vanadium dichalcogenides are highly promising candidates for spin caloritronic materials.