Charge delocalization in the ludwigite Fe₃O₂BO₃

Abstract

57 Fe Mössbauer spectra of Fe 3 O 2 BO 3 reveal a combined effect of charge ordering and electron delocalization between 112 and 450 K. On the basis of the temperature dependence of the isomer shifts and quadrupole interactions, together with the information from previously obtained transport data, we are able to discuss the arrangement of Fe 2+ and Fe 3+ in the structure and the dynamics of the electronic configurations. We found a charge-delocalization transition around 300 K. Below this temperature, formation of pairs of Fe ions with mixed valence takes place in part of the crystalline structure.

Uniaxial magnetic anisotropy in Co2.25Fe0.75OBartolomé1, Arauzo2, Kazak3 et al. 2011Phys. Rev. B

“…Although the AFM2 phase could not be discerned from NPD, MS gave evidence of this low-temperature phase when the angle θ between B hf and V zz (electric field gradient) for the different Fe sites became different from those in the AFM1 or F phase. 10,11,14 Surprisingly, the detailed magnetization anisotropy directions of the different phases in this much studied compound have not been unambiguously determined up to date, since the measurements were performed on randomly oriented powders or small collections of crystals. To unravel this question the same methodology of rotating sample magnetometry around the c axis has been applied to a Fe 3 O 2 BO 3 single crystal.…”

“…11 Above T CD the ions in the sites 2 and 4 are occupied by Fe 3+ cations with one additional electron per rung, while below T CD mixed-valence ion pairs are formed. 11 The magnetic state is paramagnetic (PM). (2) At T N1 = 112 K, there is an antiferromagnetic transition (AFM1) where the Fe 2 and Fe 4 moments become ordered, and they share one electron in a mixed-valence state.…”

“…At present there exist quite some experimental data for Fe 3 O 2 BO 3 : x-ray diffraction, 5,6,8 neutron powder diffraction (NPD), 8,9 magnetic measurements, 6,10 Mössbauer spectroscopy (MS), 5,[10][11][12][13][14] electron paramagnetic resonance, 15 and theoretical works. 7,16 The properties of this compound are summarized as follows:…”

“…(1) It undergoes a structural transition at T CD = 283 K, when being cooled, in the form of a subtle dimerization of iron ion pairs along 3LLs type I and charge localization, 6,11 while the Fe 2+ (sites 1 and 3) play no role in this transition. 11 Above T CD the ions in the sites 2 and 4 are occupied by Fe 3+ cations with one additional electron per rung, while below T CD mixed-valence ion pairs are formed. 11 The magnetic state is paramagnetic (PM).…”

Influence of Electron Delocalization on the Magnetic Properties of Iron Ludwigite Fe3O2BO3

“…The homometallic iron ludwigite Fe 3 O 2 BO 3 is an oxyborate with orthorhombic structure (see Figure 1) [1][2][3][4][5][6]. It is basically formed from two subsystems.…”