On the ‘centre of gravity’ method for measuring the composition of magnetite/maghemite mixtures, or the stoichiometry of magnetite-maghemite solid solutions, via⁵⁷Fe Mössbauer spectroscopy

Dipolar-coupled moment correlations in clusters of magnetic nanoparticles

“…3. The mean isomer shift, determined using the model independent method described by the authors Fock & Bogart et al [62], allows us to conclude that the cores have a composition of 95/5 wt% γ-Fe 2 O 3 /Fe 3 O 4 , which is in excellent agreement with that observed in our neutron diffraction measurements. Analysis of the temperature dependency of the Mössbauer spectra provides additional information about the nature of the interactions between cores.…”

“…The structural parameters refined at 300 K of both nuclear and magnetic contributions are summarized in Table A1 in the appendix. As expected for magnetite-maghemite mixtures, these measurements reveal ferrimagnetic ordering, with an average moment of 4.5(2) and 4.2(2) µ B per Fe ion at the tetrahedral and octahedral sites of the inverse spinel, respectively [62,71]. From this, we derive a net magnetic moment of 1.9(4) µ B per formula unit and a volume saturation magnetization value of 330(60) kA/m, which is close to the one calculated from the DC magnetization and discussed in the following section.…”

Unravelling the growth mechanism of the co-precipitation of iron oxide nanoparticles with the aid of synchrotron X-Ray diffraction in solution

“…The 3 min and 10 min samples were fitted using the 'center of gravity' method. 27 This method allows for the area weighted mean isomer shift of a magnetically split 57 Fe Mössbauer spectrum to be determined without the need to assume any specific underlying model for the microenvironment of the Fe atoms, provided that the data is obtained from thin, texture free absorbers and possesses a flat, well defined background and that the sample comprises magnetite/maghemite only. It is for this reason we were unable to deduce an α-value of the t = 3 min sample, since it appeared to contain an appreciable amount of ferrihydrite (ca.…”

“…The spectrum of the final product (10 min), comprises a partially collapsed magnetically split sextet pattern with very broad lines, and is indicative of magnetically blocked particles on the Mössbauer timescale, with a broad size distribution. The spectrum was fitted using the model independent 'centre of gravity' method 27 from which we surmise that the numerical proportion of Fe atoms in a magnetite environment, α, was 0.40 ± 0.17 i.e., corresponding to a mixture of magnetite and maghemite. 27 We did not observe any oxidation ageing of the material during the acquisition of any of the spectra, which took place over at least 3 d for each sample.…”

57Fe Mössbauer study of NiFe2O4 nanoparticles produced by the levitation-jet aerosol technique

“…So, the DC electric field application may aid in controlling the oxidation reactions [21,22], also providing the additional control of size, morphology and phase composition of NPs. were used to apply the initial model of the observed spectra [13,26], after which all the fitting parameters were subsequently allowed to float with the only constraint being the maintenance of the area of absorption lines ratio 3:2:1 [24]. RT spectra and best-fit spectra (lowest  2 ) are shown in Fig.…”