Kostanyan Aram, Westerström Rasmus, Zhang Yang, Kunhardt David, Stania Roland, Büchner Bernd, Popov Alexey A, Greber Thomas
Physik-Institut, Universität Zürich, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland.
Division of Synchrotron Radiation Research, Institute of Physics, University of Lund, SE-221 00 Lund, Sweden.
Phys Rev Lett. 2017 Dec 8;119(23):237202. doi: 10.1103/PhysRevLett.119.237202. Epub 2017 Dec 5.
For the endohedral fullerene molecule HoLu_{2}N@C_{80}, it is shown that the endohedral HoLu_{2}N unit may be oriented in a magnetic field. The Ho magnetic moment is fixed in the strong ligand field and aligns along the holmium-nitrogen axis. The torque of a magnetic field on the Ho magnetic moment leads to a hopping bias of the endohedral unit inclining to an orientation parallel to the externally applied field. This endohedral cluster distribution remains frozen below the onset of thermally induced rotation of the endohedral units. We derive an analytical statistical model for the description of the effect that scales below 7 T with the square of the external field strength, and that allows us to resolve the freezing temperature of the endohedral hopping motion. The freezing temperature is around 55 K and depends on the cooling rate, which in turn determines an activation energy for the hopping motion of 185 meV and a prefactor of 1.8×10^{14} s^{-1}. For TbSc_{2}N@C_{80} we find the same behavior with a 3.5% higher freezing temperature.
对于内嵌富勒烯分子HoLu₂N@C₈₀，研究表明内嵌的HoLu₂N单元在磁场中可能会发生取向。Ho磁矩在强配体场中固定，并沿钬 - 氮轴排列。磁场作用在Ho磁矩上的转矩会导致内嵌单元产生跳跃偏置，使其倾向于与外加磁场平行的取向。这种内嵌簇分布在热诱导的内嵌单元旋转开始温度以下保持冻结状态。我们推导了一个解析统计模型来描述该效应，该效应在7 T以下与外场强度的平方成正比，并且使我们能够确定内嵌跳跃运动的冻结温度。冻结温度约为55 K，并且取决于冷却速率，冷却速率反过来决定了跳跃运动的激活能为185 meV，以及一个1.8×10¹⁴ s⁻¹的前置因子。对于TbSc₂N@C₈₀，我们发现了相同的行为，但其冻结温度高3.5%。
