  As a quasi-layered ferrimagnetic material, Mn$_3$Si$_2$Te$_6$ nanoflakes
exhibit magnetoresistance behaviour that is fundamentally different from their
bulk crystal counterparts. They offer three key properties crucial for
spintronics. Firstly, at least 10^6 times faster response comparing to that
exhibited by bulk crystals has been observed in current-controlled resistance
and magnetoresistance. Secondly, ultra-low current density is required for
resistance modulation (~ 5 A/cm$^2$). Thirdly, electrically gate-tunable
magnetoresistance has been realized. Theoretical calculations reveal that the
unique magnetoresistance behaviour in the Mn$_3$Si$_2$Te$_6$ nanoflakes arises
from a magnetic field induced band gap shift across the Fermi level. The rapid
current induced resistance variation is attributed to spin-orbit torque, an
intrinsically ultra-fast process (~nanoseconds). This study suggests promising
avenues for spintronic applications. In addition, it highlights
Mn$_3$Si$_2$Te$_6$ nanoflakes as a suitable platform for investigating the
intriguing physics underlying chiral orbital moments, magnetic field induced
band variation and spin torque.
