Abstract FePd crystalline alloy with chemical stoichiometry of 1:1 is important permanent magnets and ultrahigh magnetic recording material, however there is few reports on its stable crystal structures under normal and high pressures. Thus, the stable crystal structures of FePd alloy were explored here by using particle swarm optimization algorithm and the soft-mode phase transition theory. Four new phases of FePd were discovered, namely, Imma, Cmmm-I, Cmmm-П, and P4/nmm. The structure, magnetisim, elasticity and lattice dynamics of the system were systematically investigated by first-principles calculations. It was found that the ferromagnetic state of these structures is more energetically favorable than the non-magnetic state below their respective critical pressure of ferromagnetic collapse. The phonon dispersion curves have no imaginary frequency and elastic constants fulfill Born’s criteria demonstrated that these four structures are dynamically and mechanically stable at pressure range of 0 to 59.1 GPa. These four new phases were found have negative formation enthalpy and the three orthorhombic structures were identified to be meta-stable in the pressure range of 0 to 59.1 GPa since they possess very small enthalpy difference which could not be firmly distinguished by our calculations relative to the experimentally known L10 phase. After 59.1 GPa, P4/nmm structure became the energetically most stable structure accompanied by simultaneous collapse of magnetic moments and lattice volume. The underlying mechanism was analyzed and attributed to be the simultaneously collapse of magnetoelastic force of Fe-Fe.

中文翻译：

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化学计量比为1:1的FePd结晶合金新相结构的探索

摘要 化学计量比为1:1的FePd晶体合金是重要的永磁体和超高磁记录材料，但在常压和高压下其稳定的晶体结构鲜见报道。因此，本文通过使用粒子群优化算法和软模式相变理论探索了 FePd 合金的稳定晶体结构。发现了四个新的 FePd 相，即 Imma、Cmmm-I、Cmmm-П 和 P4/nmm。通过第一性原理计算系统地研究了系统的结构、磁性、弹性和晶格动力学。发现这些结构的铁磁态在它们各自的铁磁坍塌临界压力下比非磁态在能量上更有利。声子色散曲线没有虚频，弹性常数满足 Born 标准，表明这四种结构在 0 到 59.1 GPa 的压力范围内动态和机械稳定。发现这四个新相具有负的形成焓，并且三个正交结构被确定在 0 到 59.1 GPa 的压力范围内是亚稳定的，因为它们具有非常小的焓差，我们的计算无法确定相对于实验上已知的 L10 相。在 59.1 GPa 之后，P4/nmm 结构成为能量最稳定的结构，伴随着磁矩和晶格体积的同时坍塌。分析了其潜在机制，并将其归因于 Fe-Fe 磁弹性力的同时崩溃。