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.本文报道了利用悬臂转矩磁强计法（cantilever torque magnetometry），对三种通式为[Ln(Hnic)(nic)₂(NO₃)]ₙ的镧系（Ln）手性链状配合物的螺旋自旋结构进行解析的研究，其中Hnic为烟酸（nicotinic acid），Ln分别为铽（Tb）、镝（Dy）与铒（Er）。其中镝与铒衍生物分别呈现强轴向各向异性，对应易轴各向异性（easy-axis anisotropy）与易平面各向异性（easy-plane anisotropy）；而铽衍生物则表现出显著的斜方各向异性（rhombicity）。与上述实验结果一致，交流磁化率（alternating-current susceptibility）测试仅在镝衍生物中观测到慢磁弛豫（slow magnetic relaxation）现象。将Dy³⁺（DyIII）离子掺杂至抗磁（diamagnetic）钇基同构配合物（Y-based analogue）中的实验表明，微弱的铁磁性链内相互作用（intrachain interactions）对磁化反转能垒（energy barrier for the reversal of magnetization）的贡献并不显著，该过程更符合单离子弛豫机制。此外，本研究还针对镝衍生物的两种对映异构体（enantiomers）单晶体开展了表征：利用同步辐射硬X射线（hard X-ray synchrotron radiation）在金属L边（L-edge）吸收边处进行测试，结果显示其具有光学活性（optical activity），但Dy³⁺离子的4f电子（4f electrons）对该光学活性的贡献可忽略不计。