Spin Helicity in Chiral Lanthanide Chains

We report here the
determination of the helical spin structure of three Ln-based chiral
chains of the formula [Ln­(Hnic)­(nic)2(NO3)]n (Hnic = nicotinic acid; Ln = Tb, Dy, and
Er) by means of cantilever torque magnetometry. While the Dy and Er
derivatives are strongly axial (easy-axis and easy-plane anisotropy,
respectively), the Tb derivative is characterized by a remarkable
rhombicity. In agreement with these findings, alternating-current
susceptibility reveals slow magnetic relaxation only in the Dy derivative.
Dilution of DyIII ions in the diamagnetic Y-based analogue
shows that the weak ferromagnetic intrachain interactions do not contribute
significantly to the energy barrier for the reversal of magnetization,
which is better described as a single-ion process. Single crystals
of the two enantiomers of the Dy derivative have also been investigated
using hard X-ray synchrotron radiation at the L-edge of the metal
revealing optical activity although with negligible involvement of
the 4f electrons of the DyIII ion.