Hyperfine Interact (2018) 239:17 https://doi.org/10.1007/s10751-018-1493-3 M¨ ossbauer spectroscopy control of the preparation of citric- and mandelic acid functionalized nanomagnetites A. Lengyel 1,6 · V. K. Garg 2 · A. C. de Oliveira 2 · S. W. da Silva 2 · L. R. Guilherme 3 · Z. Klencs ´ ar 4 · Z. Homonnay 1 · J. A. H. Coaquira 2 · Gy. Tolnai 5 · E. Kuzmann 1 © Springer International Publishing AG, part of Springer Nature 2018 Abstract Iron-oxide nanoparticles were prepared by two ways of chemical methods when the coprecipitated nanomagnetites were functionalized by different (citric and mandelic) carboxylic acids. The colloid samples were characterized by 57 Fe M¨ ossbauer spectroscopy, electron microscopy, RAMAN spectroscopy and magnetization measurements. Consider- able paramagnetic contributions are present in the 80 K M¨ ossbauer spectra in both citric acid coated and mandelic acid coated nanomagnetites. The 5 K measurement revealed that the paramagnetic component appearing at 80 K can represent a superparamagnetic fraction due to the small particle size in the case of mandelic acid functionalized sample. However, in the case of citric acid functionalized nanomagnetite sample, the paramagnetic compo- nents occurring also in the 5 K spectra can be associated with components of precursors and of by-product phases. Keywords 57 Fe M¨ ossbauer spectroscopy · Iron-oxide nanoparticles · Carboxylic acid coating · Superparmagnetism · Control of synthesis This article is part of the Topical Collection on Proceedings of the International Conference on the Applications of the M ¨ ossbauer Effect (ICAME 2017), Saint-Petersburg, Russia, 3–8 September 2017 Edited by Valentin Semenov  E. Kuzmann kuzmann@caesar.elte.hu 1 Institute of Chemistry, E¨ otv¨ os Lor´ and University, Budapest, Hungary 2 Department of Physics, University of Bras´ ılia, Bras´ ılia DF, Brazil 3 State University of Goi´ as, An´ apolis, Goi´ as, Brazil 4 Nuclear Analysis and Radiography Department, Centre for Energy Research, HAS, Budapest, Hungary 5 Research Centre for Natural Sciences, Hungarian Academy of Sciences, Budapest, Hungary 6 Present address: Wigner Research Centre for Physics, HAS, Budapest, Hungary