The van der Waals heterojunctions,stacking of different two-dimensional materials,have opened unprecedented opportunities to explore new physics and device concepts.Here,combining the density functional theory with no...The van der Waals heterojunctions,stacking of different two-dimensional materials,have opened unprecedented opportunities to explore new physics and device concepts.Here,combining the density functional theory with non-equilibrium Green’s function technique,we systematically investigate the spin-polarized transport properties of van der Waals magnetic tunnel junctions(MTJs),Cu/MnBi_(2)Te_(4)/MnBi_(2)Te_(4)/Cu and Cu/MnBi_(2)Te_(4)/hBN/n·MnBi_(2)Te_(4)/Cu(n=1,2,3).It is found that the maximum tunnel magnetoresistance of Cu/MnBi_(2)Te_(4)/hBN/3·MnBi_(2)Te_(4)/Cu MTJs can reach 162.6%,exceeding the system with only a single layer MnBi_(2)Te_(4).More interestingly,our results indicate that Cu/MnBi_(2)Te_(4)/h-BN/n·MnBi_(2)Te_(4)/Cu(n=2,3)MTJs can realize the switching function,while Cu/MnBi_(2)Te_(4)/h-BN/3·MnBi_(2)Te_(4)/Cu MTJs exhibit the negative differential resistance.The Cu/MnBi_(2)Te_(4)/h-BN/3·MnBi_(2)Te_(4)/Cu in the parallel state shows a spin injection efficiency of more than 83.3%.Our theoretical findings of the transport properties will shed light on the possible experimental studies of MnBi_(2)Te_(4)-based van der Waals magnetic tunneling junctions.展开更多
Valleytronics, using valley degree of freedom to encode, process, and store information, may find practical applications in low-power-consumption devices. Recent theoretical and experimental studies have demonstrated ...Valleytronics, using valley degree of freedom to encode, process, and store information, may find practical applications in low-power-consumption devices. Recent theoretical and experimental studies have demonstrated that twodimensional(2D) honeycomb lattice systems with inversion symmetry breaking, such as transition-metal dichalcogenides(TMDs), are ideal candidates for realizing valley polarization. In addition to the optical field, lifting the valley degeneracy of TMDs by introducing magnetism is an efficient way to manipulate the valley degree of freedom. In this paper, we first review the recent progress on valley polarization in various TMD-based systems, including magnetically doped TMDs,intrinsic TMDs with both inversion and time-reversal symmetry broken, and magnetic TMD heterostructures. When topologically nontrivial bands are empowered into valley-polarized systems, valley-polarized topological states, namely valleypolarized quantum anomalous Hall effect can be realized. Therefore, we have also reviewed the theoretical proposals for realizing valley-polarized topological states in 2D honeycomb lattices. Our paper can help readers quickly grasp the latest research developments in this field.展开更多
It is still an open debate whether the 1:5 H cell boundaries(CBs)or the intersections of 1:3 R platelets and1:5 H CBs are the strong pining sites for the cellular nanostructured 2:17-type Sm-Co-Fe-Cu-Zr high temperatu...It is still an open debate whether the 1:5 H cell boundaries(CBs)or the intersections of 1:3 R platelets and1:5 H CBs are the strong pining sites for the cellular nanostructured 2:17-type Sm-Co-Fe-Cu-Zr high temperature permanent magnets despite that they have been widely applied in advanced industries since 1970 s.Herein,through tuning the volume fraction of Zr-enriched 1:3 R platelets by varying the second-step aging time,the pinning behavior in a model magnet Sm_(2.5)Co_(44.9)Fe_(21.5)Cu_(5.6)Zr_(3.0)(wt%)was investigated.The results show that the volume fraction of 1:3 R platelets can be effectively enlarged without changing the cell size(i.e.the volume fraction of CBs)by extending the aging time at 400℃.Micro scopic TEM characterizations co mbined with macro scopic magnetic measurements reveals that the locally thickened 1:3 R platelets after long-term second-step aging reduce the effective pinning area by interrupting the magnetic domain walls at CBs,weakening the average pinning strength and the coercivity of the magnet.Consequently,our work supports that the 1:5 H CBs act as the dominating pinning sites instead of the intersections of 1:3 R platelets and 1:5 H CBs,which may provide an important insight towards understanding the hard magnetism of pinning-controlled permanent magnets.展开更多
基金supported the National Key Research and Development Program of China(Grant No.2022YFB3505301)the Natural Science Basic Research Program of Shanxi(Grant Nos.20210302124252,202203021222219)。
文摘The van der Waals heterojunctions,stacking of different two-dimensional materials,have opened unprecedented opportunities to explore new physics and device concepts.Here,combining the density functional theory with non-equilibrium Green’s function technique,we systematically investigate the spin-polarized transport properties of van der Waals magnetic tunnel junctions(MTJs),Cu/MnBi_(2)Te_(4)/MnBi_(2)Te_(4)/Cu and Cu/MnBi_(2)Te_(4)/hBN/n·MnBi_(2)Te_(4)/Cu(n=1,2,3).It is found that the maximum tunnel magnetoresistance of Cu/MnBi_(2)Te_(4)/hBN/3·MnBi_(2)Te_(4)/Cu MTJs can reach 162.6%,exceeding the system with only a single layer MnBi_(2)Te_(4).More interestingly,our results indicate that Cu/MnBi_(2)Te_(4)/h-BN/n·MnBi_(2)Te_(4)/Cu(n=2,3)MTJs can realize the switching function,while Cu/MnBi_(2)Te_(4)/h-BN/3·MnBi_(2)Te_(4)/Cu MTJs exhibit the negative differential resistance.The Cu/MnBi_(2)Te_(4)/h-BN/3·MnBi_(2)Te_(4)/Cu in the parallel state shows a spin injection efficiency of more than 83.3%.Our theoretical findings of the transport properties will shed light on the possible experimental studies of MnBi_(2)Te_(4)-based van der Waals magnetic tunneling junctions.
文摘Valleytronics, using valley degree of freedom to encode, process, and store information, may find practical applications in low-power-consumption devices. Recent theoretical and experimental studies have demonstrated that twodimensional(2D) honeycomb lattice systems with inversion symmetry breaking, such as transition-metal dichalcogenides(TMDs), are ideal candidates for realizing valley polarization. In addition to the optical field, lifting the valley degeneracy of TMDs by introducing magnetism is an efficient way to manipulate the valley degree of freedom. In this paper, we first review the recent progress on valley polarization in various TMD-based systems, including magnetically doped TMDs,intrinsic TMDs with both inversion and time-reversal symmetry broken, and magnetic TMD heterostructures. When topologically nontrivial bands are empowered into valley-polarized systems, valley-polarized topological states, namely valleypolarized quantum anomalous Hall effect can be realized. Therefore, we have also reviewed the theoretical proposals for realizing valley-polarized topological states in 2D honeycomb lattices. Our paper can help readers quickly grasp the latest research developments in this field.
基金Project supported by the National Natural Science Foundation of China(52071256,51901170)the Opening Project of Key Laboratory of Magnetic Molecules and Magnetic Information Materials of the Ministry of Education,China(MMMM-202003)。
文摘It is still an open debate whether the 1:5 H cell boundaries(CBs)or the intersections of 1:3 R platelets and1:5 H CBs are the strong pining sites for the cellular nanostructured 2:17-type Sm-Co-Fe-Cu-Zr high temperature permanent magnets despite that they have been widely applied in advanced industries since 1970 s.Herein,through tuning the volume fraction of Zr-enriched 1:3 R platelets by varying the second-step aging time,the pinning behavior in a model magnet Sm_(2.5)Co_(44.9)Fe_(21.5)Cu_(5.6)Zr_(3.0)(wt%)was investigated.The results show that the volume fraction of 1:3 R platelets can be effectively enlarged without changing the cell size(i.e.the volume fraction of CBs)by extending the aging time at 400℃.Micro scopic TEM characterizations co mbined with macro scopic magnetic measurements reveals that the locally thickened 1:3 R platelets after long-term second-step aging reduce the effective pinning area by interrupting the magnetic domain walls at CBs,weakening the average pinning strength and the coercivity of the magnet.Consequently,our work supports that the 1:5 H CBs act as the dominating pinning sites instead of the intersections of 1:3 R platelets and 1:5 H CBs,which may provide an important insight towards understanding the hard magnetism of pinning-controlled permanent magnets.
