A ${\mathrm{Mn}}_4$ single-molecule magnet is used to show that quantum tunneling of magnetization is not suppressed by moderate three-dimensional exchange coupling between molecules. Instead, it leads to an exchange bias of the quantum resonances which allows precise measurements of the effective exchange coupling that is mainly due to weak intermolecular hydrogen bonds. The magnetization versus applied field was recorded on single crystals of $[{\mathrm{Mn}}_4{]}_2$ using an array of micro–superconducting quantum interference devices. The step fine structure was studied via minor hysteresis loops.

• Received 26 June 2003

DOI:https://doi.org/10.1103/PhysRevB.68.140407