Distorted Mn^IVMn^III₃ Cubane Complexes as Single-Molecule Magnets

Abstract

Alternating current (ac) magnetic susceptibility data are presented for six distorted cubane complexes of the composition [MnIVMnIII 3O3X]. Each of these complexes has a well isolated S = 9/2 ground state. There is zero-field splitting (ZFS) in the ground states where D, the axial ZFS parameter, is found to be in the range of −0.27 to −0.38 cm-1. As a result of the big spin ground state and appreciable magnetic anisotropy, an out-of-phase ac magnetic susceptibility signal is seen for each of the six Mn4 complexes. The out-of-phase ac susceptibility signal reflects slow magnetization relaxation which is taken to indicate that individual molecules are acting as magnets. Alternating current susceptibility data are presented for a frozen glass of one of the Mn4 complexes to confirm that the out-of-phase ac signal is associated with isolated molecules. The factors that influence whether a given complex can function as a single-molecule magnet are described. The above Mn4 complexes represent only the second type of molecules that exhibit enough magnetic anisotropy to function as single-molecule magnets.

Landau-Zener tunneling in the presence of weak intermolecular interactions in a crystal ofMn4single-molecule magnets

“…The Landau-Zener (LZ) model has also been applied to spin tunneling in nanoparticles and molecular clusters 4,5,6,7,8,9,10,11,12 . Single-molecule magnets 13,14,15 have been the most promising spin systems to date for observing quantum phenomena like Landau-Zener tunneling because they have a well-defined structure with well-characterized spin ground state and magnetic anisotropy 16,17 . These molecules can be assembled in ordered arrays where all molecules have the same orientation.…”

Single-Molecule Magnets: Preparation and Properties of Mixed-Carboxylate Complexes [Mn12O12(O2CR)8(O2CR‘)8(H2O)4]

“…Methods 3 ] complexes to be prepared with each carboxylate type localized at specific sites on the molecule. We report the preparation and characterization of two such molecules and describe their resulting spectroscopic and magnetic properties, the latter confirming that the products retain SMM properties.…”

Determination of the magnetic anisotropy axes of single-molecule magnets

“…The values obtained in the present study are significately smaller than those reported in recent high frequency electron paramagnetic resonance (HF-EPR) studies which suggest distributions of hard-axes tilts. Single-molecule magnets (SMMs) are among the smallest nanomagnets that exhibit magnetization hysteresis, a classical property of macroscopic magnets [1,2,3,4,5]. They straddle the interface between classical and quantum mechanical behavior because they also display quantum tunneling of magnetization [6,7,8,9,10,11,12,13,14] and quantum phase interference [15,16].…”