Iron–magnesium compounds under high pressure†
Magnesium (Mg) and iron (Fe) are almost immiscible under ambient conditions; this makes Mg an unusual candidate to be considered as a main light element in the earth's core; on the other hand, recent studies have shown that a significant amount of Mg can be dissolved in Fe to form Fe–Mg compounds under high pressure as high pressure can sufficiently improve the solubility of Mg in Fe. However, the formation mechanism and structures of the Fe–Mg compounds are still unknown to date. Herein, we proposed a series of unexpected Fe–Mg compounds (FeMg4, FeMg3, FeMg2, Fe2Mg3, FeMg and Fe2Mg) using the CALYPSO structure search method in conjunction with first-principles calculations. The results show that valence electrons of the Mg atoms transfer to the Fe atoms under high pressure, leading to the formation of these Fe–Mg compounds. This study represents a significant step forward in the understanding of binary Fe–Mg compounds.