磁场诱导[Mn $^{\textrm{III}}$（taa）]自旋交叉跃迁的X射线吸收谱研究
Magnetic-field-induced spin-crossover transition in [Mn$^{\textrm{III}}$(taa)] studied by X-ray absorption spectroscopy
摘要：
研究了自旋交叉化合物[Mn $^{\textrm{III}}$（taa）]中Mn在高达37 T的脉冲强磁场中的X射线吸收近边结构（XANES）。通过对低温低自旋（LS）态施加磁场，观察到光谱的显著变化，表明磁场诱导的自旋交叉到高自旋（HS）态。在低温下，磁场依赖的光谱中的变化表现出滞后。此外，当磁场设置为零时，观察到相当大的反射分量。HS $\to$ LS跃迁的能垒由反射信号的衰减时间的温度依赖性评估。发现该跃迁的能垒为134K，明显低于以前报道的其他自旋交叉化合物的能垒。由于场致HS态的分数最多为30%，并且热动力学宏观场致相变预计发生在高于55 T的场中，所以在低至17 K的低温下观察到的场致相变可以理解为单分子水平上的局部微观相变。
英文摘要：
The X-ray absorption near-edge structure (XANES) of Mn in a spin-crossover compound, [Mn$^{\textrm{III}}$(taa)], was studied in pulsed high magnetic fields up to 37T. By applying magnetic fields to the low-temperature low-spin (LS) state, significant changes in the spectra were observed, suggesting a magnetic-field-induced spin-crossover to the high-spin (HS) state. At low temperatures, the magnetic field dependence of the changes in the spectra exhibited hysteresis. Furthermore, when the magnetic field was set to zero, a considerable remanent component was observed. The energy barrier of the HS $\to$ LS transition was evaluated from the temperature dependence of the decay time of the remanent signal. The energy barrier of the transition was found to be 134K, which is notably lower than that for other spin-crossover compounds reported previously. Since the fraction of the field-induced HS state was at most 30% and the thermodynamic macroscopic field-induced phase transition was expected to occur in fields higher than 55T, the observed field-induced transition at low temperatures down to 17K could be understood as a localized microscopic transition at the single-molecular level.
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