高压下铁系元素及合金宏观铁磁稳定性研究

The pressureress is a powerful tool to investigate the complex relationship between structure and magnetism. At ambient conditions iron group and alloys are typical ferromagnetism. However stability of ferromagnetism is broken out under high pressure with absence of ferromagnetism. This is due to pressure-induced change of crystal structure. The phenomenons of ferromagnetic instability caused by the change of crystal structure is studied systematically and the same rule is found out. It is helpful for understanding the correlation between structural phase transition and magnetic phase transition, and understanding the essence of ferromagnetism. Therefore, it is very important to study the general law of the ferromagnetism stability of under pressure. Based on previous work, a high sensitivity of situ AC susceptibility measurement system will be employed. The Macroscopic magnetic parameters such as AC susceptibility and Curie temperature will be measured. The boundary conditions of ferromagnetic stability in iron group under high pressure and temperature will defined. Moreover alloy stability boundary under high pressure will be measure too. Base on the measurement, a ferromagnetism stability phase diagram will be set up. The general rules of pressure- induced ferromagnetic instability will be summarized. With the high pressure structure diagram, the effect of regulation in the ferromagnetic stability boundary depending the crystal structure is point out. The important problems which the program will solve are less higher pressure experiment and the influence of pressure on the stability of alloy .

压力是研究物质结构与磁性之间复杂关系有效的手段。铁系元素及合金在常规条件下具有典型的铁磁性，但是在一定的压力下铁磁性的稳定状态被打破，铁磁性逐渐减弱直至消失，这是由于压力对晶体结构的改变而导致的。对此现象进行系统地研究，找出共性规律，有助于认知结构相变与磁性相变的关联性，理解铁磁性来源的本质。因此，研究铁磁性在压力作用下稳定存在边界条件就十分关键。结合已有工作基础，利用基于金刚石对顶砧的高灵敏度原位磁性测量系统，通过对交流磁化率，居里温度等宏观磁性参数的测量，从宏观磁性角度对高温高压下铁系元素以及高压下合金的铁磁稳定性边界条件进行界定，建立铁磁稳定性相图；总结掺杂比对于合金在高压下铁磁性稳定性的影响的一般规律；结合高压结构相图，阐述晶体结构对铁磁性稳定存在条件的调控作用。重点解决当前研究中高压力下宏观铁磁稳定边界、高压对合金稳定性影响的共性规律问题。

在高压下，寻找晶体结构改变与磁性转变之间的复杂关系，对于理解铁磁性来源的本质具有重要的意义。高压下的样品通常仅有几十微米，因此需要灵敏度极高的磁性测量系统，才能够对压致磁性转变进行准确的测量。本课题分别从高压实验技术及高压下铁磁性物质磁性测量进行研究，探索出了制约高压下磁性测量灵敏度和信噪比的多种因素，并有针对性地对原有高压下磁性测量系统进行了改进，将测量信噪比提高为原来的5.3倍，实现了对接近200GPa下铁磁性样品磁性转变的测量。利用改进的高灵敏度磁性测量系统，对铁、钴、镍、铁钴合金在高压下的磁性转变进行了测量，建立了铁、钴、镍以及不同配比铁钴合金的铁磁性稳定相图；进一步通过测量不同配比的铁钴合金，绘制了压力、元素比例在铁钴合金铁磁稳定性影响的曲线。所探索的高压下磁性测量制约因素对于高压下磁性测量实验具有指导意义，得到的数据为进一步明晰晶体结构变化在铁磁稳定性被破坏过程中的作用以及结构相变与磁性相变之间的内在联系提供了重要的依据。