Abstract We report the discovery of a low-temperature spin-flop transition in 5C pyrrhotite at ~155 K that is similar to those seen in hematite at 260 K and FeS (troilite) at 440 K. The 5C crystal was produced by annealing a 4C pyrrhotite crystal at 875 K to produce a change in the vacancy-ordering scheme that developed during cooling. The 5C structure is confirmed by single-crystal X‑ray diffraction and the stoichiometry and homogeneity by electron microprobe and SEM BSE mapping. Resonant ultrasound spectroscopy (RUS), heat capacity, and magnetization measurements from room temperature down to 2 K are reported. The transition is marked by a steep change in elastic properties at the transition temperature, a peak in the heat capacity, and weak anomalies in measurements of magnetization. Magnetic hysteresis loops and comparison with the magnetic properties of 4C pyrrhotite suggest that the transition involves a change in orientation of moments between two different antiferromagnetic structures, perpendicular to the crystallographic c-axis at high temperatures and parallel to the crystallographic c-axis at low temperatures. The proposed structures are consistent with a group theoretical treatment that also predicts a first-order transition between the magnetic structures.

中文翻译：

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5C磁黄铁矿中的莫林型转变

摘要 我们报告了在 ~155 K 的 5C 磁黄铁矿中的低温自旋翻转转变的发现，类似于 260 K 的赤铁矿和 440 K 的 FeS（硫磷矿）。5C 晶体是通过对 4C磁黄铁矿晶体在 875 K 下产生冷却过程中形成的空位排序方案的变化。5C 结构通过单晶 X 射线衍射和电子微探针和 SEM BSE 映射的化学计量和均匀性得到证实。报告了从室温到 2 K 的共振超声光谱 (RUS)、热容量和磁化测量。转变的标志是转变温度下弹性特性的急剧变化、热容量的峰值以及磁化测量的弱异常。磁滞回线和与 4C 磁黄铁矿的磁特性的比较表明，转变涉及两种不同反铁磁结构之间的矩取向的变化，高温下垂直于晶体 c 轴，低温下平行于晶体 c 轴. 所提出的结构与组理论处理一致，该处理也预测了磁结构之间的一阶跃迁。