  The realization of multiferroicity in 2D nanomaterials is crucially important
for designing advanced nanoelectronic devices such as non-volatile multistate
data storage. In this work, the coexistence of ferromagnetism and
ferroelectricity is reported in monolayer SnTe system by transition metal (TM)
doping. Based on first-principles calculations, the spontaneous spin
polarization could be realized by TM doping in ferroelectric SnTe monolayer. In
addition to in-plane ferroelectric polarization, the out-of-plane ferroelectric
polarization emerges in Mn (Fe)-doped SnTe monolayer due to the internal
displacement of TM from the surface. Interestingly, the crystalline field
centered on TM and interaction between the dopant and Te gradually enhanced
with the increment of atomic number of doping elements, which explains why the
formation energy decreases. The realization of multiferroics in SnTe monolayer
could provide theoretical guidance for experimental preparation of
low-dimensional multiferroic materials.
