Magnetic hysteresis and strong ferromagnetic coupling of sulfur-bridged Dy ions in clusterfullerene Dy(2)S@C(82) †

Two isomers of metallofullerene Dy(2)S@C(82) 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 Dy(2)S@C(82) 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 Dy(2)S@C(82) molecule flips at once as a single entity.