Manipulation Of Spin And Valley Polarizations In Ferromagnetic Van Der Waals Heterojunction

Two-dimensional materials have attracted attention for their excellent performance and diverse heterostructure stacking characteristics.To date,various researches have been carried out at the micro and nano scales in various fields.The van der Waals layered structure provides opportunities to study the interaction of light and matter in the 2D monolayer limit,for example,in single-layer transition metal dichalcogenide（TMDs）materials（such as WSe₂）,spin-valley coupling occurs due to the broken spatial inversion symmetry together with spin-orbital coupling.Recently,long-range magnetic orders have discovered,in monolayer CrI₃ and Cr₂Ge₂Te₆,providing a platform for studying the interaction of magneto-optical effect.CrI₃ is a typical material with a Curie temperature（Tc）of⁶1 K,the ferromagnetism depends on the number of layers.The odd layers show ferromagnetic（FM）,and the even layers display antiferromagnetic（AFM）.CrI₃ can reaches its saturation magnetization in an external magnetic field of⁰.1 T.In a van der Waals heterojunction comprising TMDs two-dimensional materials and CrI₃,the magnetic proximity effect influences the spin and valley polarization of TMDs material,these properties are of great significance for spintronics and valley electronics.In this paper,we studied the magnetic proximity effect in the CrI₃ and WSe₂heterostructure.The polarization-resolved PL of WSe₂ in the heterojunction were investigated under a magnetic field from-3 T to+3 T,the proximity magnetic field of CrI₃ is controlled by an external magnetic field.PL intensities and valley splitting in monolayer WSe₂ switched due to the switch of magnetization and direction of the proximity magnetic field.We further studied the influence of the magnetic proximity effect of CrI₃-WSe₂ and CrI₃-graphene 2D van der Waals heterostructures on the magnetic resistance of WSe₂ and graphene.In electrical devices of CrI₃ and WSe₂,CrI₃ and graphene,we measured the magnetic resistance of CrI₃-WSe₂ heterojunction and CrI₃-graphene heterostructure under a magnetic field from-7 T to+7 T at a temperature of 300 K and 10 K,and the gate voltage was changed at the same time.For the CrI₃-graphene van der Waals heterojunction,we observed that the magnetic resistance shows different dependence under the influence of external magnetic field and the gate voltage.And the maximum change ratio of magnetic resistance is 3.14%.This paper used a more direct measurement method to verify the magnetic proximity effect of the CrI₃ and WSe₂heterostructures and focused on exploring the magnetic resistance of the ferromagnetic van der Waals heterojunction composed of CrI₃.This paper also contributed to the study of the electrical characteristics of the ferromagnetic two-dimensional van der Waals heterojunction,and accumulated experience for subsequent research.