Gd $_6$ FeBi $_2$磁体中高有序温度的理解：临界行为、电子结构和晶场分析
Understanding high ordering temperature in Gd$_6$FeBi$_2$ magnet: critical behavior, electronic structure and crystal-field analysis
摘要：
Gd 6 FeBi 2被报道为唯一一种居里温度（Tc）为约100 ℃的室温磁体。350 K，在数百种具有其结构类型的化合物中，这使得它在潜在的应用中更具吸引力。为了揭示这种高有序温度的起源，本文研究了Gd_6 FeBi_2的临界行为、电子结构和晶场效应。短程Gd-Fe亚铁磁相互作用由非居里-外斯顺磁行为、晶体和电子结构分析支持，与先前的DFT计算一致。与强的TM-TM交换作用不同，Gd-Fe交换作用对长程交换作用决定的临界指数的影响有限，这似乎是不含TM-TM交换作用的RE-TM基合金的共同特征。然而，强的Gd-Fe杂化降低了电子振动耦合对短程交换相互作用的影响，从而允许高Tc。Gd 4f-电子带的加宽或分裂机制是基于晶场分析来解决的，并且可能是Gd 6 FeBi 2和Gd基化合物中具有非磁性元素的Tc升高的另一个因素。讨论了同结构化合物的不同磁性行为，以及能带分裂与晶场效应的关系。
英文摘要：
Gd6FeBi2 is reported as the only one room-temperature magnet with a Curie temperature (Tc) of ca. 350 K among more than hundreds of compounds with its structural type, which makes it more attractive in potential applications. To reveal the origin of such high ordering temperature, critical behaviors, electronic structure and crystal-field effects of Gd6FeBi2 are investigated in this work. The short-range Gd-Fe ferrimagnetic interaction is supported by the non-Curie-Weiss paramagnetic behavior, crystal and electronic structure analyses, in agreement with previous DFT calculations. Unlike the strong TM-TM exchange interactions, the Gd-Fe exchange interaction shows limited influence on the critical exponents determined by long-range exchange interactions, which seems a common feature in RE-TM based alloys without TM-TM exchange interactions. However, the strong Gd-Fe hybridization reduces the influence of vibronic couplings on the short-range exchange interaction and thus allows a high Tc. The broadening or splitting mechanism of Gd 4f-electron bands is addressed based on crystal-field analysis and likely another factor for elevated Tc in Gd6FeBi2 and Gd-based compounds with non-magnetic elements. Different magnetic behaviors among isostructural compounds, and the relationship between the band splitting and crystal-field effects is also discussed.
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