VI₃—a New Layered Ferromagnetic Semiconductor

Abstract

Two-dimensional (2D) materials are promising candidates for next-generation electronic devices. In this regime, insulating 2D ferromagnets, which remain rare, are of special importance due to their potential for enabling new device architectures. Here we report the discovery of ferromagnetism in a layered van der Waals semiconductor, VI 3 , which is based on honeycomb vanadium layers separated by an iodine-iodine van der Waals gap. It has a BiI 3 -type structure (R-3, No.148) at room temperature, and our experimental evidence suggests that it may undergo a subtle structural phase transition at 78 K. VI 3 becomes ferromagnetic at 49 K, below which magneto-optical Kerr effect imaging clearly shows ferromagnetic domains, which can be manipulated by the applied external magnetic field. The optical band gap determined by reflectance measurements is 0.6 eV, and the material is highly resistive.

Crystal structures and phase transitions of the van der Waals ferromagnet VI3

“…The RT structure of VI3, refined from the XRSCD data, is trigonal which is in agreement with most literature sources [14,15,18,19]. The same R-3 (148) space group has been reported in [13,15,19]. The trigonal structure persists upon cooling down to 80 K as evidenced by the unchanged set of measured diffraction peaks.…”

“…The refinement of the RT VI3 crystal structure by the analysis of 792 independent diffraction peaks collected at 250 K provides the trigonal R-3 (148) space group as the best solution. Two possible structure models are suggested in literature: a) R-3 (148) [14,19] or b) P-31c (163) [18]. The present refinement of the structure with the space group R-3 (148) quickly converged with excellent R values (see Table S1 in Supplemental Material [26]) with refined twin-volume fractions.…”

“…This idea can be further specified when knowing microscopic aspects of the magnetic structures which are most probably not simple. Somewhat canted ferromagnetic structures have been suggested in previous papers [19,21]. Therefore, investigations focused on details of the magnetism of VI3 are strongly desired.…”

“…Son et al [18] report the RT trigonal structure P-31c (163), a structural phase transition at Ts = 79 K and monoclinic crystal symmetry C2/c (17). Kong et al [19] have determined the trigonal structure R-3 (148) at 100 K and suggest a subtle structural phase transition at 78 K. In contrast, Tian et al [20] claim that the structural phase transition of VI3 is analogous to the structural transition of CrI3, i.e. between the HT monoclinic structure C2/m (15) (determined at 100 K) and the LT rhombohedral structure R-3 (148) determined at 60 and 40 K).…”

Critical behavior and magnetocaloric effect in VI3

“…Besides this, the magnetic domain creep, i.e., the magnetic domain walls jump from one pinning site to another, can also lead to this kind of irreversible behavior. 14 The evolution of ferro-magnetic domain as a function of magnetic field and temperature was further investigated, 13 confirming the ferromagnetism and a small domain-wall-energy in VI 3 . It should be noted that there is an additional weak anomaly at 80 K for H c * [inset in Fig.…”