  Spin-mechanical coupling is vital in diverse fields including spintronics,
sensing and quantum transduction. Two-dimensional (2D) magnetic materials
provide a unique platform for investigating spin-mechanical coupling,
attributed to their mechanical flexibility and novel spin orderings. However,
studying spin-mechanical coupling in 2D magnets presents challenges in probing
mechanical deformation and thermodynamic properties change at nanoscale. Here
we use nano opto-electro-mechanical interferometry to mechanically detect the
phase transition and magnetostriction effect in multilayer CrSBr, an air-stable
antiferromagnets with large magnon-exciton coupling. The transitions among
antiferromagnetism, spin-canted ferromagnetism and paramagnetism are visualized
by optomechanical frequency anomalies. Nontrivial magnetostriction coefficient
2.3x10^(-5) and magnetoelastic coupling strength on the order of 10^6 J/m^3
have been found. Moreover, we demonstrate the substantial tunability of the
magnetoelastic constant by nearly 50% via gate-induced strain. Our findings
demonstrate the strong spin-mechanical coupling in CrSBr and paves the way for
developing sensitive magnetic sensing and efficient quantum transduction at
atomically thin limit.
