It has been observed that some 3d or 4f isolated metal-­ion-­containing complexes show a static magnetic field induced thermally activated magnetic relaxation and the absence of slow relaxation is explained by the fast quantum tunneling mechanism. Due to the prominent spin orbit coupling effect, several lanthanide and actinide-­containing mononuclear molecules were discovered to be single-­ion magnets (SIM)s. Of particular interest are the SIMs containing a lanthanoid ion sandwiched by cyclooctatetraene di-­anion (COT) and pentamethylcyclopentadiene anion (Cp*). The single-ion feature of these molecular nanomagnets makes them close to the microscopic scale compared with typical cluster-­based single molecular magnets, and as a result the quantum aspects seem more prominent. We propose to characterise the magnetic dynamics of these materials with mSR.