Site-Selective Magnetic Moment Collapse in Compressed Fe₅O₆

Abstract

Iron oxide is one of the most important components in the Earth’s mantle. The recent discovery of the stable presence of Fe5O6 in the Earth’s mantle environment has stimulated significant interests in understanding of this new category of iron oxides. We report the electronic structure and magnetic properties of Fe5O6 calculated by the density functional theory plus dynamic mean field theory (DFT + DMFT) approach. Our calculations indicate that Fe5O6 is a conductor at ambient pressure with dominant Fe-3d density of states at the Fermi level. The magnetic moments of iron atoms at three non-equivalent crystallographic sites in Fe5O6 collapse at significantly different rates under pressure. This site-selective collapse of magnetic moments originates from the shifting of energy levels and the consequent charge transfer among the Fe-3d orbits when Fe5O6 is being compressed. Our simulations suggest that there could be high conductivity and volume contraction in Fe5O6 at high pressure, which may induce anomalous features in seismic velocity, energy exchange, and mass distribution in the deep interior of the Earth.

Evolution of electrical conductivity and semiconductor to metal transition of iron oxides at extreme conditions

“…For example, DFT+DMFT calculation results reveal that the total density of states of Fe 5 O 6 at the Fermi level is dominated by the Fe-3d bands and possesses bulky quasi-particle peaks, which indicates that Fe 5 O 6 is metallic at high pressure. [60] Employing the same calculation method, the electronic conduction in Fe 4 O 5 is constrained by the Fe-3d bands, which are dominant by the total density of states at the Fermi level E F . [61] They conclude that Fe 4 O 5 stays metallic nature from ambient conditions through the core-mantle boundary (up to 140 GPa).…”

Orthogonal magnetic structures of Fe4O5: representation analysis and DFT calculations

“…Since the discovery of novel high-pressure iron oxides, their crystal chemistry and physical properties have been of great interest. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] Based on the common packing motif, these compounds constitute a homologous series nFeO•mFe 2 O 3 , containing η-Fe 2 O 3 , HP-Fe 3 O 4 , Fe 4 O 5 , Fe 5 O 6 , Fe 5 O 7 , etc. 4 Their crystal structures consist of two main building blocks, namely the slabs of edge-shared Fe-O octahedra separated by arrays of one-dimensional (1D) chains of Fe ions coordinated by a trigonal prism (see Fig.…”

“…3,7 Interestingly, the majority of these oxides feature iron ions in the mixed-valence state resulting in a sizeable conductivity 3,7,11 and intricate charge-ordering transitions at low temperatures, 3,7,12 similar to the famous Verwey transition in magnetite Fe 3 O 4 . 16 At high pressures, a site-selective spin transition is expected in these oxides 15,8,10 that should have a serious effect on the electronic structure.…”

Electronic properties of single-crystalline Fe4O5

“…46,47 To date, the electronic properties of Fe 4 O 5 have been controversially reported in the literature. While band structure calculations predicted a metallic nature of both Fe 4 O 5 48 and Fe 5 O 6 , 49 recent experiments showed seemingly semiconducting properties of Fe 4 O 5 and its metallization was observed only under high pressure above 80 GPa at room temperature. 50,51 A typical splitting of the d-orbitals of Fe 2+ (3d 6 ) and Fe 3+ (3d 5 ) ions in highly-symmetric octahedral and trigonal-prismatic oxygen coordinations 52,53 is depicted in Fig.…”