Department of Engineering Sciences and Mathematics, University of Applied Sciences Bielefeld, D-33602 Bielefeld, Germany.
J Phys Condens Matter. 2010 Jun 2;22(21):216007. doi: 10.1088/0953-8984/22/21/216007. Epub 2010 May 5.
We show that intramolecular exchange disorder recently found in the geometrically frustrated magnetic molecules {Mo(72)Fe(30)} and {Mo(72)Cr(30)} leads, in a classical Heisenberg model description, to spin freezing and slow magnetization dynamics reminiscent of spin glass behaviour. Also we suggest that our low temperature and low magnetic field nuclear magnetic resonance (NMR) measurements on {Mo(72)Fe(30)}, showing rapid and strong broadening of the proton line width on cooling below 600 mK, are evidence for a crossover from paramagnetic behaviour to a frozen spin configuration. Similar broadening is observed in {Mo(72)Cr(30)}. This observed effect is consistent with our theory of spin freezing and slow magnetization dynamics in these systems due to exchange disorder.
我们表明，最近在几何上受挫的磁性分子 {Mo(72)Fe(30)} 和 {Mo(72)Cr(30)} 中发现的分子内交换无序，在经典海森堡模型描述中，导致自旋冻结和类似于自旋玻璃行为的缓慢磁化动力学。此外，我们还提出，我们对 {Mo(72)Fe(30)} 的低温和低磁场核磁共振（NMR）测量结果表明，在冷却到 600 mK 以下时，质子线宽迅速且强烈变宽，这表明从顺磁行为到冻结的自旋构型发生了交叉。在 {Mo(72)Cr(30)} 中也观察到类似的展宽。这种观察到的效应与我们在这些系统中由于交换无序导致自旋冻结和缓慢磁化动力学的理论一致。
