Crystallographic and magnetic structures of the VI3 and LiVI3 van der Waals compounds

Two-dimensional (2D) layered magnetic materials are generating a great amount of interest for the next generation of electronic devices thanks to their remarkable properties associated with spin dynamics. The recently discovered layered VI3 ferromagnetic phase belongs to this family, although a full understanding of its properties is limited by the incomplete understanding of its crystallographic structure. The motivation of this work is to address this issue. Here, we investigate the VI3 crystal structures at low temperature using both synchrotron x-ray and neutron powder diffraction and provide structural models for the two structural transitions occurring at 76 and 32 K. Moreover, we confirm by magnetic measurements that VI3 becomes ferromagnetic at 50 K and we question the establishment of a long-range magnetic structure by neutron diffraction. We equally determined the magnetic properties of our recently reported LiVI3 phase, which is like the well-known CrI3 ferromagnetic phase in terms of electronic and crystallographic structures and found an antiferromagnetic behavior with a Ned temperature of 12 K. Such a finding provides extra clues for a better understanding of magnetism in these low-dimension compounds. Finally, the easiness of preparing Li-based 2D magnetic materials by chemical/electrochemical means opens wide the opportunity to design materials with exotic properties.

Automated summary

Two-dimensional layered magnetic materials, such as the recently discovered VI3 ferromagnetic phase, have sparked great interest due to their unique spin dynamics properties, but incomplete understanding of their crystallographic structures remains a challenge. This study investigated VI3 crystal structures at low temperature using synchrotron x-ray and neutron powder diffraction, revealing structural models for the two-phase transitions and questioning the establishment of a long-range magnetic structure. Additionally, the magnetic properties of the LiVI3 phase, similar to CrI3 in electronic and crystallographic structures, were examined, showing antiferromagnetic behavior and providing insights for a better understanding of magnetism in low-dimensional compounds.