Low-spin ground state of the giant single-molecule magnets {Mn70} and {Mn84}

Abstract

The single-molecule magnets {Mn70} and {Mn84} are characterized by a 14-site unit cell with S=2 spin sites arranged in a circular geometry. Experimentally, these systems exhibit a magnetic ground state with a notably low total spin Stot=5–7. Up to now, this low-spin ground state has been up difficult to describe theoretically due to the complexity of the quantum Heisenberg model for such a large system. In this paper, we fill this gap and demonstrate that the ground state of {Mn70} and {Mn84} is in fact governed by a small, finite Stot in quantitative agreement with the experiment. We employ accurate, large-scale SU(2)-symmetric density-matrix renormalization group calculations for a quantum Heisenberg model with previously published exchange parameters obtained by density-functional theory. We do not find a low-spin state for the same parameters and S=1 and thus propose that frustrated systems with S≥2 are inherently prone to weak ferromagnetic interactions. This could account for the prevalence of similar low-spin Mn-based single-molecule magnets. Finally, we compute the full magnetization curve and find wide plateaus at 10/14, 11/14, 12/14, and 13/14 of the saturation, which can be traced back to nearly independent three-site clusters with broken intercluster bonds. Published by the American Physical Society 2025