高压下有序晶态合金Fe_3Pt的低能声子不稳定性及磁性反常

Low energy phonon instabilities and magnetic abnormalities in ordered crystalline state alloys of Fe_3Pt at high pressure

有序晶态Fe3Pt因瓦合金处于一种特殊的磁临界状态,这种磁临界状态下体系的晶格动力学稳定性对压力极为敏感.基于密度泛函理论的第一性原理的投影缀加平面波方法研究了不同晶态合金的Fe3Pt的焓和磁性随压力的变化规律,结果表明,在压力小于18.54 GPa下,P4/mbm结构是热力学稳定的相.Pmˉ3m结构、I4/mmm结构、DO22结构的Fe3Pt在铁磁性坍塌临界压力附近体系的总磁矩急剧下降并具有振荡现象,且I4/mmm结构和DO22结构的Fe3Pt在临界压力附近出现了Fe1原子磁矩反转现象.在43 GPa下,DO22结构的Fe3Pt出现了亚铁磁微观磁特性突然增强且伴随着体积突然增大的现象.在高压下,对Pmˉ3m结构Fe3Pt的晶格动力学计算表明,压力小于26.95 GPa的铁磁态下体系的自发磁化诱导了体系横向声学支声子软化,表明体系中存在很强的自发体积磁致伸缩.特别是在铁磁性坍塌临界压力41.9 GPa至磁性完全消失的57.25 GPa压力区间,晶格动力学稳定性对压力更加敏感.压力大于57.25 GPa时,压力诱导了体系声子谱的稳定.

The ordered crystalline Fe3Pt inv^r alloy is in a special magnetic critical state under which the la^tme aynamlc stability of the system is extremely sensitive to the external pressure. Using projection augmented plane wave method based on the density functional theory, we calculate the dependences of enthalpy and magnetism of different crystalline alloys of Fe3Pt on external pressure. The results reveal that the P4/mbm structure is thermodynamically stable under pressures below 18.54 GPa. The total magnetic moments of Pm3ra, I4/mrnm and DO22 structures decrease rapidly and oscillate near the ferromagnetic collapse critical pressure. Furthermore in I4/mmm and D022 structures the atomic magnetic moment of Fel reverses near the critical pressure. At a pressure of 43 GPa, the micro-ferrimagnetic property in DO~ structure becomes apparently strengthened while its volume increases rapidly. The lattice dynamic calculation shows that the spontaneous magnetization of the system in ferromagnetic states induces the softening of the transverse acoustic phonon TA1 （M） in the FeaPt of Pm3m structure, and there exists a strong spontaneous volume magnetostriction at pressures below 26.95 GPa. Especially, in the pressure range between the ferromagnetic collapse critical pressure 41.9 GPa and the magnetism completely disappearing pressure 57.25 GPa, the lattice dynamic stability is more sensitive to the pressure. The pressure induces the stability of the phonon spectrum of the system at pressures above 57.25 GPa.