  The antiferromagnetic topological insulator MnBi2Te4 (MBT) exhibits an ideal
platform to study exotic topological phenomena and magnetic properties. The
transport signatures of magnetic phase transitions in the MBT family materials
have been well-studied. However, their mechanical properties and
magneto-mechanical coupling have not been well-explored. We use
nanoelectromechanical systems to study the intrinsic magnetism in MBT thin
flakes via their magnetostrictive coupling. We investigate mechanical resonance
signatures of magnetic phase transitions from antiferromagnetic (AFM) to canted
antiferromagnetic (cAFM) to ferromagnetic (FM) phases versus magnetic field at
different temperatures. The spin-flop transitions in MBT are revealed by
frequency shifts of mechanical resonance. With temperatures going above TN, the
transitions disappear in the resonance frequency map, consistent with transport
measurements. We use a magnetostrictive model to correlate the frequency shifts
with the spin-canting states. Our work demonstrates a technique to study
magnetic phase transitions, magnetization and magnetoelastic properties of the
magnetic topological insulator.
