Mössbauer characterisations and magnetic properties of iron cobaltites CoxFe3−xO4 (1≤x≤2.46) before and after spinodal decomposition

Abstract

Iron cobaltite powders Co x Fe 3 À x O 4 (1 r xr 2.46) were synthesized with compositions in between the cobalt ferrite CoFe 2 O 4 and Co 2.46 Fe 0.54 O 4. The cationic distribution of pure spinel phases was determined by Mössbauer spectroscopy: as Co content increases in the spinel oxide, Co 3 þ cations replace Fe 3 þ cations in the octahedral sites and Co 2 þ cations migrate from octahedral to tetrahedral sites. Saturation magnetizations M S measured at 5 K by a SQUID magnetometer were consistent with the values calculated from the cationic distribution. M S decreases as diamagnetic Co 3 þ cations replace strongly magnetic Fe 3 þ cations. Two spinel phases were formed by spinodal decomposition of Co 1.73 Fe 1.27 O 4 phase submitted to a subsequent thermal treatment, one with a high amount of iron Co 1.16 Fe 1.84 O 4 and one other containing mostly cobalt Co 2.69 Fe 0.31 O 4. Increase of the experimental M S value obtained after the spinodal decomposition is in accordance with the calculated value deduced from the cationic distribution of the two phases.

Structural and magnetic properties of Co Fe3−O4 versus Co/Fe molar ratio

“…An additional doublet with increasing intensity is present in case of T2.0 and T2.5. The Mössbauer parameters of the quadrupole doublet are close to those reported by Le Trong et al [21]. The quadrupole doublet indicates the presence of paramagnetic ferrite.…”

“…3 shows the Mössbauer spectra of T0.5-T2.5 samples calcined at 1000°C, together with the computer fit (continuous lines). These are very similar to the spectra of cobalt ferrites obtained by other methods described in literature [21,30]. The Mössbauer spectrum of T0.5 indicates the presence of hematite (α-Fe 2 O 3 ) in addition to the spinellic phase.…”

“…The quadrupole doublet indicates the presence of paramagnetic ferrite. It is known that Curie temperature (Tc) of the Co x Fe 3 À x O 4 decreases with the increase of the cobalt content [21]. Mössbauer parameters obtained by fitting the spectra with Lorentzian line shape are given in Table 4.…”

“…Its magnetic properties are mainly determined by the Co 2 þ , and thus the tuning of its magnetic properties by adjusting the Co/Fe ratio become possible [20]. By thermal treatment, the Co x Fe 3 À x O 4 is slowly transformed in two iron-rich and cobalt-rich spinel phases [21]. The paramagnetic behavior of Co x Fe 3 À x O 4 (x¼ 0.5-1.5) synthesized by redox reaction between Co and Fe nitrates and 1.2-etanediol were higher than in case of 1,2-propanediolul and 1,3-propanediol, respectively [22][23][24][25].…”

Cobalt-iron Oxide, Alloy and Nitride: Synthesis, Characterization and Application in Catalytic Peroxymonosulfate Activation for Orange II Degradation

“…In the case of CFA-500 and CFA-600, the spectra (Figure 5a,b) mainly reflect the presence of Fe 3+ in the CoFe2O4 spinel phase with a partial degree of inversion. CoFe2O4 is known to prefer a partially inverse spinel structure where majority of the A (tetrahedral) site is taken by Fe 3+ [27,28]. We can observe three components corresponding to Fe 3+ in tetrahedral (A) site (sextet), octahedral (B) site (sextet with broad peaks reflecting binomial distribution of cobalt atoms at the tetrahedral site) and the smallest particles with superparamagnetic nature (quadrupole doublet).…”