The crystalline structure and Fe local environment in a Co-doped Ni–Fe–Ga Heusler alloy, prepared by the melt-spinning technique, were investigated by X-ray diffraction (XRD) and EXAFS at room and low temperatures. The characteristic temperatures of the austenite–martensite phase transitions were determined by differential scanning calorimetry via cooling and heating cycles of the alloy ribbons. As shown by room-temperature XRD, the austenitic phase of the alloy has the chemically ordered L2₁ Heusler structure. This was confirmed by EXAFS, although this technique was not able to conclusively distinguish between the L2₁ and B2 structures of the austenite for the analyzed alloy. The low-temperature martensitic phase and its structural evolution towards austenite with increasing temperature were studied by high-energy X-ray diffraction, which evinced the martensite modulation. However, the Fe environment could be fitted by EXAFS with the tetragonal L1₀ structure of the non-modulated martensite. This proves that the martensite modulation has structural effects on a long-range scale, without significant changes in the short-range order around the atoms. The changes in the local structure around iron on martensitic transformation were correlated with changes in the electronic structure, described by XANES spectroscopy at the Fe K edge.

中文翻译：

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Ni52Co2Fe20Ga26 铁磁赫斯勒合金中的长程和短程有序

在室温和低温下通过 X 射线衍射 (XRD) 和 EXAFS 研究了通过熔体纺丝技术制备的 Co 掺杂的 Ni-Fe-Ga Heusler 合金的晶体结构和 Fe 局部环境。奥氏体-马氏体相变的特征温度由差示扫描量热法通过合金带的冷却和加热循环确定。如室温 XRD 所示，合金的奥氏体相具有化学有序的 L2 ₁ Heusler 结构。EXAFS 证实了这一点，尽管该技术无法最终区分 L2 ₁分析合金的奥氏体的 B2 结构。通过高能 X 射线衍射研究了低温马氏体相及其随着温度升高向奥氏体的结构演变，表明马氏体调制。然而，铁环境可以通过 EXAFS 与非调制马氏体的四方 L1 ₀结构拟合。这证明马氏体调制在长程尺度上具有结构效应，而原子周围的短程有序没有显着变化。马氏体转变过程中铁周围局部结构的变化与电子结构的变化相关，由 Fe K边缘的XANES 光谱描述。