Single phase charge ordered stoichiometric CaFe3O5 with commensurate and incommensurate trimeron ordering

Abstract

Mixed-valent transition metal compounds display complex structural, electronic and magnetic properties which can often be exquisitely tuned. Here the charge-ordered state of stoichiometric CaFe3O5 is probed using neutron powder diffraction, Monte Carlo simulation and symmetry analysis. Magnetic ordering is dominated by the formation of ferromagnetic Fe3+–Fe2+–Fe3+ trimers which are evident above the magnetic ordering transition. Between TN = 289 K and 281 K an incommensurate magnetically ordered phase develops due to magnetic frustration, but a spin Jahn-Teller distortion lifts the frustration and enables the magnetic ordering to lock in to a charge-ordered commensurate state at lower temperatures. Stoichiometric CaFe3O5 exhibits single phase behaviour throughout and avoids the phase separation into two distinct crystallographic phases with different magnetic structures and Fe valence distributions reported recently, which likely occurs due to partial Fe2+ for Ca2+ substitution. This underlines the sensitivity of the magnetism and chemistry of these mixed-valent systems to composition.

Extended “orbital molecules” and magnetic phase separation in Bi0.68Ca0.32MnO3

“…Recently, a reliable CO superstructure model was proposed [10], showing the formation of three Fe site units over which the localized electrons are distributed. This linear ferromagnetic units, called trimerons, are also observed in other Fe-based oxides showing CO transitions like CaFe 3 O 5 [11,12] and Fe 4 O 5 [13]. The formation of dimers [14], trimers [10][11][12], and more complex d-metal clusters [15][16][17] in solid-state systems, usually referred to as "orbital molecules" [18,19], is a fascinating phenomenon involving the competition of various degrees of freedom, such as charge, orbital, and magnetic ordering [10][11][12][15][16][17]19,20].…”

A Room‐Temperature Verwey‐type Transition in Iron Oxide, Fe5O6

“…A variety of the charge‐ordering features observed in octahedral networks of iron oxides studied to date suggests the existence of several competing mechanisms of these phenomena. In general, one expects that the type of charge ordering is mainly influenced by the electron count and spin arrangement, should the magnetic ordering precede the charge‐ordering transition.…”

Structure and magnetic properties of epitaxial CaFe2O4 thin films

“…6a) exhibits a sharp PM doublet without any trace of magnetic parasitic phases containing Fe. Therefore, we can exclude contamination by iron oxides or other calcium ferrite phases with higher T N , such as brownmillerite Ca 2 Fe 2 O 5 27 or CaFe 3 O 5 28,29 . A high-resolution CEMS spectrum recorded at RT in a narrow velocity scale is reported in Fig.…”