  Single-molecule magnets (SMMs) exhibiting open hysteresis loops may
potentially apply to molecule-based information processing and storage.
However, the capacity to retain magnetic memory is always limited by zero-field
quantum tunneling of magnetization (QTM). Herein, a well-designed dysprosium
metallacrown SMM, consisting of an endohedral approximate linear F-Dy-F strong
anisotropic moiety in a peripheral [15-MCNi-5] metallacrown (MC), is reported
with the largest reversal barrier of 1060 cm-1 among d-f SMMs. Rectangle-like
hysteresis loops are observed with the huge squareness (remanence/saturation
magnetization) up to 97% at 2 K. More importantly, zero-field QTM step is
phenomenologically removed by minimizing the dipole coupling and hyperfine
interactions. The results demonstrate for the first time that zero-field QTM
step can be eliminated via manipulating the ligand field and vanishing the
external magnetic perturbations, which illuminates a promising blueprint for
developing high-performance SMMs.
