Magnetic Order and Its Interplay with Structure Phase Transition in van der Waals Ferromagnet VI3

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 similar to 36 degrees 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 similar to 1.3 mu (B) at 4 K is much lower than the fully ordered spin moment of 2 mu (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.