低溫高磁場X光吸收能譜

Low-temperature High-field X-ray Absorption Spectroscopies

秦伊瑩(Yi-Ying Chin)

《科儀新知》 228期 (2021/09) Pp. 51-62

摘要

本文簡介以低溫高磁場X光吸收能譜來研究BaCoO_3及TbFe_3(BO_3)_4。前者的有效磁矩大於1.73 μ_B，暗示非零的軌道磁矩，然而其晶體結構傾向磁量子數為零的基態；藉由X光磁圓偏振二向性實驗與理論模擬，我們發現Co之間的交互作用會造成能階的反轉，導致Co具有非零的軌道磁矩。後者在低溫會轉變為反鐵磁相，因Tb與Fe皆具有磁矩，我們利用X光線偏振二向性實驗確認其反鐵磁結構；此外，我們亦在不同磁場下進行實驗，以釐清其磁化量突然抬升背後的機制。

並列摘要

In this manuscript, the X-ray absorption spectroscopy studies on BaCoO_3 and TbFe_3(BO_3)_4 under high magnetic field are briefly introduced. For BaCoO_3, the effective magnetic moment (2.23 μ_B) extracted from the magnetic susceptibility is larger than 1.73 μ_B (the value without any orbital moment), while its crystal structure prefers the hole occupation of the a1g orbital with m = 0. Combining the X-ray magnetic circular dichroism and theoretical calculations, we found that the short distance between Co ions along the c axis makes the a1g orbital lower in energy and thus leads to the finite orbital moment. On the other hand, we employed X-ray linear dichroism to determine the antiferromagnetic structure of TbFe_3(BO_3)_4 and performed experiments under various magnetic field to investigate the significant enhancement of the magnetization in the antiferromagnetic phase.