| Spintronics,exploiting electron spin degree of freedom as an information carrier,has become a research hotspot for new devices in the post-Moore era.Based on the Mermin-Wagner theory,the intrinsic two-dimensional magnetic material has been missing.Until 2017,intrinsic ferromagnetism was discovered at the monolayers CrI3 and CrGeTe3,and the two-dimensional van der Waals magnetic materials have received great attention.Two-dimensional magnetic materials have unique magnetic properties and abundant spin physics phenomena,and have important research significance in frontier fields such as spintronics,topological physics,and materials science.Firstly,owing to its van der Waals structure,the two-dimensional magnetic material is easy to exfoliate to a single layer,which provides an ideal platform for studying the magnetic properties under the limit of two-dimensional conditions and layer-dependent magnetism.At the same time,compared with traditional magnetic thin films,two-dimensional van der Waals ferromagnets are easy to form heterostructure,and can manipulate the way of interlayer stacking(torsion,periodic strain or materials with lattice mismatch to form moire pattern structure)to give rise to a series of novel and unique physical phenomena.Recently,the family of two-dimensional magnetic materials has developed rapidly.However,their Curie temperatures are relatively low,far below room temperature,which hindered the application prospects of room temperature spintronics in the field of two-dimensional magnetic materials.The two-dimensional room temperature ferromagnet 1 T-CrTe2 is in the early stage due to the complicated preparation methods.In this paper,we focus on the two-dimensional room temperature ferromagnets 1 T-CrTe2 and Cr self-intercalation CrTe2 and explore their magnetic properties and low-temperature electromagnetic transport.The research contents of this paper mainly include the following aspects:(1)Study on the controllable synthesis of room temperature van der Waals ferromagnet 1T-CrTe2 and its giant anomalous Hall effect.The 1T-CrTe2 compound was obtained by oxidation of KCrTe2 with iodine(I2)in acetonitrile.The low-temperature Hall effect shows that 1T-CrTe2 has a clossal anomalous Hall effect:the anomalous Hall angle and electric conductivity can reach 5.5%and 1.33×106 cm-1,respectively.The linear relationship between the anomalous Hall conductivity and the longitudinal conductivity indicates that this huge anomalous Hall effect is dominated by the extrinsic skew scattering mechanism.Meanwhile,owing to its layered structure and high-quality crystal quality,1T-CrTe2 has extremely high longitudinal conductivity.Considering its huge anomalous Hall effect and extremely high longitudinal conductivity,1 T-CrTe2 is expected to host great potential to.serve as a spin current generation with high energy efficiency.(2)The study of magnetic anisotropy control based on Cr atom self-intercalation layer 1T-CrTe2.Perpendicular magnetic anisotropy is a key factor in charge-spin conversion and all-electric magnetic moment regulation in high-performance magnetic storage devices.By self-intercalation of native Cr atom into van der Waals gap of 2D CrTe2,the in-plane anisotropy of CrTe2 can be tuned into PMA accompanied with its high Tc.More strikingly,the Cr-intercalated CrTe2 ferromagnetic material also exhibits high saturation magnetization(>200 emu/cm3),high conductivity(>104 ?-1cm-1),large anomalous Hall angle and giant anomalous Hall factor(?0.23 at 200 K,0.18 at 300 K)compared to other popular ferromagnets.Our work not only discovers a new material,Cr-CrTe2,which bears the full potential to serve as a building block for spintronic devices,but also offers a new approach to control the magnetic anisotropy in layered materials.(3)Further magnetic analysis shows that Cr-CrTe2 has more abundant magnetic properties.Due to the RKKY interactions and other competitive magnetic interactions,Cr-CrTe2 have a spin canting magnetic structure.The electromagnetic transport results show that when the magnetic field is along the c axis,Cr-CrTe2 shows a skew scattering dominated anomalous Hall effect;when the magnetic field is along the ab plane,the topological Hall effect is observed.The temperature and thickness-dependent topological Hall effect indicated that in addition to the intrinsic spin chirality,the thermal fluctuations can further enhance the THE at elevated temperature.Our work shows that Cr-CrTe2 has great application potential in van der Waals spintronic devices based on spin chirality in the future.(4)We further systematacially studied the planar Hall effect(PHE)and anisotropic magnetoresistance(AMR)of Cr-CrTe2.Electromagnetic transport results show spin-dependent scattering dominates the large in-plane AMR and PHE,persisting to room temperature.When an external magnetic field rotates along the z-x plane,a strong fourfold AMR at low temperature and high field is observed,distinct from the traditional twofold AMR,which is attributed to high term lattice symmetry.Our findings prove the application potential of Cr-CrTe2 in magnetic recording and magnetic field sensing equipment,and provide valuable insights for high-order AMR in layered magnetic materials. |
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