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This work focuses on utilizing the X‐ray diffraction technique as an alternative method to specialized and high‐cost techniques such as X‐ray photoelectron spectroscopy to obtain the cation distribution in magnetic nanoparticles as MFe2O4 with spinel structure synthesized by thermal decomposition. X‐ray diffraction measurements for MFe2O4 with M = Co2+ as transition cation (inverse spinel CoFe2O4) showed sensitivity to the cation distribution for octahedral and tetrahedral sites in this material with this kind of crystalline structure, being a good option for its determination. The cation distribution was obtained from the X‐ray diffraction intensity ratios for the most sensitive crystalline planes to the cations in octahedral and tetrahedral sites. Besides, the Debye–Scherrer equation and line profile analysis method from the diffraction pattern were used to determine the size distribution and the crystallite size. The size distribution obtained by X‐ray diffraction was from 15 to 18 nm, while transmission electron microscopy was found to be from 10 to 25 nm. The inversion degree x derived from X‐ray diffraction exhibits variability within the interval 0.6 < x < 0.8, not very far from that obtained by X‐ray photoelectron spectroscopy (x = 0.67). This material exhibits a saturation magnetization of 124.88 emu g−1. Consequently, the X‐ray diffraction technique opens the possibility of obtaining reliable information related to nanoparticles' morphological and chemical properties with spinel structure. [ABSTRACT FROM AUTHOR]

The genus Chloephaga Eyton, 1838, consisting of four species that breed in Patagonia, encompasses anatids endemic to South America. Despite their prominence in the present-day avifauna, these species have left behind a limited fossil record. The aim of the present contribution is to describe Chloephaga fossils coming from Middle Pleistocene levels (San José Sequence) cropping out at Bajo San José site, southwestern Buenos Aires Province, Argentina. The specimens are referred to three different taxa, including a new species, Chloephaga dabbenei n. sp., a smaller but indeterminate taxon, which is also probably a new species, and the extant species C. picta (J.F.Gmelin, 1789). The newly described species is notably large, falling within the upper size range observed in males of C. picta. The tarsometatarsus is straight-shafted with poorly divergent distal trochleae, features that are correlated with cursorial habits, that are absent in other members of Chloephaga. The co-occurrence of three species of the genus Chloephaga is registered nowadays in the Argentine Patagonia and in the southeast of Buenos Aires Province, when they migrate during the winter season. [ABSTRACT FROM AUTHOR]