Physical Mechanisms of Exchange Coupling Effects in Nanoparticulate Diluted Magnetic Oxides Obtained by Laser Pyrolysis

• Published in: Journal of physical chemistry. C 2017-04, Vol.121 (16), p.9063-9069
• Main Authors: Kuncser, Victor Eugen, Schinteie, Gabriel Alexandru, Kuncser, Andrei Cristian, Leca, Aurel, Scarisoreanu, Monica, Morjan, Ion, Filoti, George
• Format: Article
• Language: English
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/acs.jpcc.7b01500

TiO2 nanoparticles, undoped and doped with Fe, have been prepared by laser pyrolysis and further investigated with respect to morphological, structural and magnetic aspects by transmission electron microscopy, diffractometry, Mössbauer spectroscopy, and magnetometry. The obtained nanoparticles, consisting of mainly anatase phase, agglomerate in clusters of tenths of units and present a large size distribution in the range from 5 to 40 nm. The anatase to rutile weight ratio (about 9) and the morphology of particles is similar in all analyzed samples (doped by up to 12 at. % Fe). Only Fe3+ ions in high spin configuration were observed mainly at the surface of TiO2 nanoparticles, either distributed or forming fine clusters of Fe oxide. Both a paramagnetic phase and a superparamagnetic one with blocking temperature lower than 50 K are superposed over a long-range ferromagnetic phase specific to diluted magnetic oxide systems. The influence of doping Fe ions on the magnetic behavior of each phase is discussed in detail. Evidences for interface exchange couplings (with unidirectional anisotropy in specific conditions) between the long-range ferromagnetic phase and the fine clusters (antiferromagnetic in nature), which become frozen below the blocking temperature of 50 K, are provided. The specificity of the processing route and the physical mechanisms responsible for the observed relevant magnetic features, which can be tailored for suitable applications, are discussed.