Magnetic Order and Its Interplay with Structure Phase Transition in van der Waals Ferromagnet VI3 Supported by the Innovation Program of Shanghai Municipal Education Commission (Grant No. 2017-01-07-00-07-E00018), the Shanghai Municipal Science and Technology Major Project (Grant No. 2019SHZDZX01), and the National Natural Science Foundation of China (Grant No. 11874119). E.F. and H.C. acknowledge the support of U.S. DOE BES

Abstract

Van der Waals magnet VI3 demonstrates intriguing magnetic properties that render it great for use in various applications. However, its microscopic magnetic structure has not been determined yet. Here, we report neutron diffraction and susceptibility measurements in VI3 that revealed a ferromagnetic order with the moment direction tilted from the c-axis by ∼36° at 4 K. A spin reorientation accompanied by a structure distortion within the honeycomb plane is observed, before the magnetic order completely disappears at T C = 50 K. The refined magnetic moment of ∼1.3 μ B at 4 K is much lower than the fully ordered spin moment of 2μ B/V3+, suggesting the presence of a considerable orbital moment antiparallel to the spin moment and strong spin–orbit coupling in VI3. This results in strong magnetoelastic interactions that make the magnetic properties of VI3 easily tunable via strain and pressure.