Field-induced oscillation of magnetization blocking barrier in a holmium metallacrown single-molecule magnet

Single-molecule magnets (SMMs) exhibit magnetization blocking in the presence of strong magnetic anisotropy. By employing molecular engineering, the blocking barrier can be significantly modified, remaining independent from other external factors, such as magnetic field. Taking advantage of hyperfine coupling of electronic and nuclear spins further highlights their unique functionality. However, a poor understanding of relaxation mechanisms limits the exploitation of nuclear-spin molecular qubits. Here, we report the first observation of field-dependent oscillation of the magnetization blocking barrier in a holmium metallacrown magnet driven by the switch of relaxation mechanisms involving hyperfine interaction. First-principles calculations reveal an activated temperature dependence of magnetic relaxation, dominated either by incoherent quantum tunneling of magnetization at anti-crossing points or by Or-bach-like processes at crossing points. This mechanism demonstrates that these relaxation barriers can be consecutively switched by increasing the external field, which paves a way for manipulating magnetization dynamics of SMMs using hyperfine interaction.