  Two-dimensional (2D) materials with robust magnetism have drawn immense
attention for their promising applications in spintronics. Recently, intrinsic
ferromagnetic vanadium triiodide (VI3) has been synthesized experimentally. To
enhance its spintronic property, we modified VI3 by interstitial doping with 3d
transition metals (TM) and used first-principles calculations to investigate
the geometric structure, formation energy, electronic property, and magnetism
of pristine VI3 and 3d TM-doped VI3 monolayer. Among eight transition metal
(Sc-, Ti-, V-, Cr-, Mn-, Fe-, Co-, and Ni-) doped VI3 materials, four of them
(Ti-, V-, Mn-, and Ni-doped VI3) show robust magnetism with full spin
polarization near the Fermi energy. Our research demonstrates that Ti-doped VI3
results in half-metallic semiconductor properties (HMS), while V-doped VI3 and
Ni-doped VI3 result in half-semiconductor properties (HSC). Surprisingly,
Mn-doped VI3 exhibits an unusual bipolar magnetic semiconductor property (BMS).
This unique combination of strong ferromagnetism and 100% spin polarization
with a half-metallic, half-semiconductor, or bipolar semiconductor property
renders 3d TM-doped VI3 as potential candidates for next generation
semiconductor spintronic applications. These spin-polarized materials will be
extremely useful for spin-current generation and other spintronic applications.
