Magnetic properties of Fe-Ni and Fe-Si alloys under pressure: Confrontation of SQUID magnetometer and Mössbauer spectroscopy measurements

铁和镍以及硅和硫等轻合金元素被认为是类地行星核心的主要成分。关于高压下类地行星核心中的铁或材料的磁性方面的知识非常少。这些知识对于理解行星核中磁场的产生是很重要的。六方封闭堆积(HCP)状态对于地球内核中的Fe和Fe-Ni合金是有利的。到目前为止，hcp-Fe的磁性状态仍然存在争议。利用超导量子干涉仪(SQUID)和穆斯堡尔谱的对峙数据，我们发现在19.2 GPa时，铁仍然具有可测量的剩余磁化强度，而穆斯堡尔谱中由超精细分裂产生的六重态完全消失。对于任何对磁学感兴趣的人，特别是对高压研究感兴趣的人来说，了解SQUID磁强计和穆斯堡尔光谱分析结果之间差异背后的原因是至关重要的。Fe68Ni32和Fe64Ni36在居里温度分别为128℃和227℃的常温下具有铁磁性。它们的居里点分别漂移了-45K/Gpa和-35K/Gpa，这意味着在~3 Gpa和~6 Gpa以上，它们应该成为顺磁性的。在我们的实验中，可测量的铁磁剩余磁化强度在Fe64Ni36中持续到16.3 Gpa，并且在减压后立即变得更具磁性。我们想在Fe68Ni32上确认这一点，并与Fe68Ni32和Fe64Ni36对抗穆斯鲍尔。在我们的实验中，我们还发现SIRM和六重峰强度在压力下有很好的相关性。实现这一目标的机制尚不清楚。重要的是要验证这种关系是否可以在其他样品上重复。BCC-Fe91Si09是一个很好的候选材料。它在环境条件下是铁磁性的。在Fe中合金化Si后，体心立方Fe91Si09在室温下稳定在50 Gpa以下。重要的是，我们的初步工作表明，Fe91Si09的SIRM随着压缩到20 Gpa而不断增加，在减压后还会继续增加。在此，我们建议对因瓦区Fe-Ni合金(Fe68Ni32和Fe64Ni36)和Fe-Si合金(Fe91Si09)在高压下的磁化进行进一步的研究：在一个非磁性的金刚石顶压室中继续对峙SQUID磁强计和Mössbasuer谱。

Iron together with nickel and light alloying elements such as silicon and sulfur, is believed to be the major constituent in cores of terrestrial planets. There is very little knowledge on magnetic properties of iron or materials in cores of terrestrial planets under high pressure. Such knowledge is important for understanding generation of magnetic field in planetary cores. Hexagonal closed packed (hcp) state is favored for Fe and Fe-Ni alloys in Earth’s inner core. By far, the magnetic state of hcp-Fe remains contentious. By confront superconducting quantum interference device (SQUID) magnetometer data with Mössbauer spectroscopy, we found that iron at 19.2 GPa still possessed a measurable remanent magnetization, whereas the sextets from hyperfine splitting in the Mössbauer spectra had completely disappeared. Understanding the origin behind the discrepancy between the SQUID magnetometer and Mössbauer spectroscopy results is of fundamental importance for anyone interested in magnetism, and especially those interested in high-pressure research. Fe68Ni32 and Fe64Ni36 are ferromagnetic at ambient condition with Curie temperatures of 128°C and 227°C, respectively. Their Curie points shift by about -45 K/GPa and -35 K/GPa, which means above ~3 GPa and ~6 GPa they should become paramagnetic. In our experiments, a measurable ferromagnetic remanent magnetization persists in Fe64Ni36 up to 16.3 GPa and becomes much more magnetic immediately upon decompression. We would like to confirm this on Fe68Ni32 and confront both Fe68Ni32 and Fe64Ni36 against Mössbauer. In our experiments, we also found that SIRM and sextet peak intensities correlated well under pressures. The mechanism for this is unclear. It is important to verify whether such a relationship is repeatable on other samples. Bcc-Fe91Si09 is a good candidate. It is ferromagnetic at ambient conditions. With Si alloyed in Fe, bcc Fe91Si09 is stable up to 50 GPa at room temperature. Importantly, our preliminary work suggests that the SIRM of Fe91Si09 constantly increases with compression up to 20 GPa and further still upon decompression. Here, we propose a further study on magnetization of Fe-Ni alloys around invar range (Fe68Ni32 and Fe64Ni36) and Fe-Si alloy (Fe91Si09) under high pressures: continue confrontation SQUID magnetometer and Mössbasuer spectroscopy in one non-magnetic diamond anvil cell.