Superexchange interactions and magnetic microstructures of oxyfluoride ferrospinels

Bashkirov, Sh. Sh.; Liberman, A. B.; Manenkova, L. K.; Men, A. N.; Khasanov, Airat

doi:10.1007/bf00897451

Cited by 3 publications

(2 citation statements)

References 3 publications

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“…11 As part of our modeling analysis for substitution effects on ET, we present calculated substitution energetics for various possible substitution patterns, which affords another chance for model validation by comparison with experimental observables beyond what was done in the previous study. Here we examine the effects on ET of some of the most common substitutions, namely, replacement of Fe by Al 3+ or Mg 2+ and replacement of OH − groups by F − .…”

Section: Introductionmentioning

confidence: 99%

Effects of compositional defects on small polaron hopping in micas

Rosso

Ilton

2005

The Journal of Chemical Physics

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Hartree-Fock calculations and electron transfer (ET) theory were used to model the effects of compositional defects on ET in the brucite-like octahedral sheet of mica. ET was modeled as an Fe(IIIII) valence interchange reaction across shared octahedral edges of the M2-M2 iron sublattice. The model entails the hopping of localized electrons and small polaron behavior. Hartree-Fock calculations indicate that substitution of F for structural OH bridges increases the reorganization energy lambda, decreases the electronic coupling matrix element V(AB), and thereby substantially decreases the hopping rate. The lambda increase arises from modification of the metal-ligand bond force constants, and the V(AB) decrease arises from reduction of superexchange interaction through anion bridges. Deprotonation of an OH bridge, consistent with a possible mechanism of maintaining charge neutrality during net oxidation, yields a net increase in the ET rate. Although substitution of Al or Mg for Fe in M1 sites distorts the structure of adjacent Fe-occupied M2 sites, the distortion has little net impact on ET rates through these M2 sites. Hence the main effect of Al or Mg substitution for Fe, should it occur in the M2 sublattice, is to block ET pathways. Collectively, these findings pave the way for larger-scale oxidation/reduction models to be constructed for realistic, compositionally diverse micas.

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Section: Introductionmentioning

confidence: 99%

Effects of compositional defects on small polaron hopping in micas

Rosso

Ilton

2005

The Journal of Chemical Physics

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“…This effect can be seen in the site-projected DOS of YCaFe 2 O 5 F, shown in Supporting Information. Weakened superexchange is frequently observed in distorted perovskite oxides when octahedral tilting decreases the orbital overlap, but replacing O with F has an even greater effect, as shown in several experiments. − For instance, pseudocubic AgFeOF 2 with very little tilting has a Neél temperature of 480 K, much lower than that of the tilted perovskites SrFeO 2 F ( T N = 710 K) or LaFeO 3 ( T N = 740 K), which might be expected to have weaker superexchange due to their tilts. In another experiment, fluorination of La 2 NiO 4+d to La 2 NiO 3 F 2 reduced the Neél temperature from 330 to 49 K, despite the fact that the oxidation state of Ni remained the same .…”

Section: Resultsmentioning

confidence: 97%

Multiferroism in Iron-Based Oxyfluoride Perovskites

2018

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Multiferroic materials with simultaneous magnetic and ferroelectric ordering that persist above room temperature are rare. Using first-principles density functional theory calculations, we demonstrate fluorination of oxygen-deficient AA'FeO perovskites, where A and A' are cations with +3 and +2 oxidation states, respectively, and have a layered ordering, as an effective strategy to obtain room-temperature multiferroics. We show that by controlling the size of the A and A' cations, it is possible to stabilize a noncentrosymmetric phase arising due to the hybrid improper ferroelectricity mechanism, with polarization as high as 13 μC/cm. The fluorination also stabilizes Fe in +3 oxidation state, which results in superexchange interactions that are strong enough to sustain magnetic order well above room temperature. We also show the presence of a magnetoelectric coupling wherein the switching mode that reverses the direction of the spontaneous polarization also affects the strength of the magnetic interactions. The results show that low-temperature fluorination of anion-deficient perovskites with layered cation ordering can be an effective approach to design new multiferroics.

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