@article{10902/24772,
year = {2017},
month = {6},
url = {http://hdl.handle.net/10902/24772},
abstract = {We evaluate the application of 57Fe Mössbauer spectroscopy to the determination of the composition of magnetite (Fe3O4)/maghemite (?-Fe2O3) mixtures and the stoichiometry of magnetite-maghemite solid solutions. In particular, we consider a recently proposed model-independent method which does not rely on a priori assumptions regarding the nature of the sample, other than that it is free of other Fe-containing phases. In it a single parameter, ?RT-the 'centre of gravity', or area weighted mean isomer shift at room temperature, T = 295 ± 5 K - is extracted by curve-fitting a sample's Mössbauer spectrum, and is correlated to the sample's composition or stoichiometry. We present data on high-purity magnetite and maghemite powders, and mixtures thereof, as well as comparison literature data from nanoparticulate mixtures and solid solutions, to show that a linear correlation exists between ?RT and the numerical proportion of Fe atoms in the magnetite environment: ? = Femagnetite/Fetotal = (?RT - ?o)/m, where ?o= 0.3206 ± 0.0022 mm s-1 and m = 0.2135 ± 0.0076 mm s-1. We also present equations to relate ? to the weight percentage w of magnetite in mixed phases, and the magnetite stoichiometry x = Fe2+/Fe3+ in solid solutions. The analytical method is generally applicable, but is most accurate when the absorption profiles are sharp; in some samples this may require spectra to be recorded at reduced temperatures. We consider such cases and provide equations to relate ?(T) to the corresponding ? value.},
organization = {This work was supported by the European Union Seventh Framework Programme through the NanoMag project ‘Nanometrology standardisation methods for magnetic nanoparticles’, under grant agreement no. 604448},
publisher = {IOP Publishing},
publisher = {Journal of Physics D: Applied Physics, Vol. 50, Iss. 26, Art. Num. 265005 (2017)},
title = {On the 'centre of gravity' method for measuring the composition of magnetite/maghemite mixtures, or the stoichiometry of magnetite-maghemite solid solutions, via 57Fe Mössbauer spectroscopy},
author = {Fock, Jeppe and Bogart, Lara Katrina and González Alonso, David and Espeso Martínez, José Ignacio and Hansen, Mikkel Fougt and Varón, Miriam and Frandsen, Cathrine and Pankhurst, Quentin A.},
}