ABSTRACT A high pressure low-temperature neutron diffraction study has been carried out on rare earth metal Dysprosium (Dy) to 10.8 GPa and 8 K in a large-volume diamond anvil cell using a spallation neutron source. Dy crystallizes in an ambient pressure hexagonal close packed phase and forms an incommensurate helical antiferromagnetic phase, marked by the appearance of superlattice magnetic peaks below 176 K with a turn-angle between the hexagonal layers that increases both with increasing temperature and pressure. The ferromagnetic transition below 87 K is marked by an increase in intensity of nuclear peaks with disappearance of magnetic superlattice reflections. Dy transforms to an alpha-Samarium (α-Sm) phase at 7 GPa and only ferromagnetic ordering is observed for this high pressure phase. The ferromagnetic transition is observed at 59 K in the α-Sm phase at 10.8 GPa in close agreement with the magnetic ordering temperature obtained from electrical transport measurements. In the entire pressure-temperature range of this study, Dy shows a negative thermal expansion coefficient of as much as −2.5% in the magnetically ordered phases between 200 and 8 K.

中文翻译：

---

大体积金刚石砧座电池中子衍射研究揭示的稀土金属镝的磁序

摘要 使用散裂中子源在大体积金刚石砧室中对稀土金属镝 (Dy) 进行了高压低温中子衍射研究（Dy）至 10.8 GPa 和 8 K。Dy 在环境压力的六方密堆积相中结晶并形成不相称的螺旋反铁磁相，其特征是出现低于 176 K 的超晶格磁峰，六方层之间的转角随着温度和压力的增加而增加。低于 87 K 的铁磁转变的标志是核峰强度增加，磁性超晶格反射消失。Dy 在 7 GPa 时转变为 α-钐 (α-Sm) 相，并且在该高压相中仅观察到铁磁有序。在 10.8 GPa 的 α-Sm 相中，在 59 K 处观察到铁磁转变，这与从电输运测量中获得的磁有序温度非常一致。在本研究的整个压力-温度范围内，Dy 在 200 和 8 K 之间的磁有序相中显示出高达 -2.5% 的负热膨胀系数。