Abstract
Two isomers of metallofullerene Dy2S@C82 with sulfur-bridged Dy ions exhibit broad magnetic hysteresis with sharp steps at sub-Kelvin temperature. Analysis of the level crossing events for different orientations of a magnetic field showed that even in powder samples, the hysteresis steps caused by quantum tunneling of magnetization can provide precise information on the strength of intramolecular Dy⋯Dy inter-actions. A comparison of different methods to determine the energy difference between ferromagnetic and antiferromagnetic states showed that sub-Kelvin hysteresis gives the most robust and reliable values. The ground state in Dy2S@C82 has ferromagnetic coupling of Dy magnetic moments, whereas the state with antiferromagnetic coupling in C s and C 3v cage isomers is 10.7 and 5.1 cm−1 higher, respectively. The value for the C s isomer is among the highest found in metallofullerenes and is considerably larger than that reported in non-fullerene dinuclear molecular magnets. Magnetization relaxation times measured in zero magnetic field at sub-Kelvin temperatures tend to level off near 900 and 3200 s in C s and C 3v isomers. These times correspond to the quantum tunneling relaxation mechanism, in which the whole magnetic moment of the Dy2S@C82 molecule flips at once as a single entity.
Highlights
Tremendous progress in lanthanide single-molecule magnets (SMMs) during the last decade had been largely fuelled by the design of new molecules with ever-increasing magnetic anisotropy.1 For single-ion SMMs, ligand-field (LF) splitting has been the main parameter on which experimental and computational studies have focused until recently,2 the gradual understanding of the paramount role of molecular vibrations shifts the focus to spin–phonon interactions.2j,3 In polynuclear SMMs, exchange and dipolar interactions between lanthanide ions create a more complex structure of magnetic states than in single-ion magnets, and the presence of such coupled states introduces a strong variation in staticAside from compounds with lanthanide-radical coupling, which can be very strong,5 magnetic Ln⋯Ln interactions are usually rather weak
For single-ion SMMs, ligand-field (LF) splitting has been the main parameter on which experimental and computational studies have focused until recently,2 the gradual understanding of the paramount role of molecular vibrations shifts the focus to spin–phonon interactions.2j,3 In polynuclear SMMs, exchange and dipolar interactions between lanthanide ions create a more complex structure of magnetic states than in single-ion magnets, and the presence of such coupled states introduces a strong variation in static aLeibniz Institute for Solid State and Materials Research, Helmholtzstraße 20, 01069
The first dinuclear Endohedral metallofullerenes (EMFs)-SMM Dy2ScN@C80-Ih revealed the strong influence of Dy⋯Dy interactions on the magnetic hysteresis shape in comparison with mononuclear DySc2N@C80, and indicated a considerable ΔEAFM–FM energy of ca. 6 cm−1.4d Since we studied a number of di-nuclear EMFs and found a strong variation of the strength of Dy⋯Dy interactions in them
Summary
Tremendous progress in lanthanide single-molecule magnets (SMMs) during the last decade had been largely fuelled by the design of new molecules with ever-increasing magnetic anisotropy.1 For single-ion SMMs, ligand-field (LF) splitting has been the main parameter on which experimental and computational studies have focused until recently,2 the gradual understanding of the paramount role of molecular vibrations shifts the focus to spin–phonon interactions.2j,3 In polynuclear SMMs, exchange and dipolar interactions between lanthanide ions create a more complex structure of magnetic states than in single-ion magnets, and the presence of such coupled states introduces a strong variation in staticAside from compounds with lanthanide-radical coupling, which can be very strong,5 magnetic Ln⋯Ln interactions are usually rather weak. The very high density of crossing events near this threshold field translates into sharp QTMA features in the magnetic hysteresis curves (Fig. 1 and 2), which allows accurate estimation of ΔEAFM–FM.
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