Atomic Scale Study on the Thermal Evolution of Local Structure and Magnetic Properties in Oleic Acid Coated Iron Oxide Nanoparticles

Abstract

The physics of the binding of nanoparticles of goethite and cubic iron oxide as capped by oleic acid has been elucidated in the present study based on the thermal evolution of local structure and magnetic properties using Mossbauer spectroscopy. It is observed that the goethite nanoparticles predominantly undergo topotactic transformation to hemeatite while the assembly of identical bare (not oleic acid capped) nanoparticles composed of goethite and magnetite are subjected to annealing beyond 520 K. In contrast to the results obtained on the bare nanoparticles, accelerated reduction of oleic acid coated nanoparticles of goethite to fully stoichiometric magnetite and subsequently to wustite and α-Fe is observed in the 750−875 K annealing interval. Atomic scale characterization of core−shell structures of different iron oxide phases obtained during the evolution of oleic acid coated nanoparticles of iron oxides has also been provided. The understanding of the present study could be utilized to obtain desired core−shell structures of iron oxides, providing the scope for studying the exchange interaction between the core and shell structures, which exhibit different magnetic ordering.

Atomic scale insights on the growth of BiFeO3 nanoparticles

“…Importantly the Mössbauer results clearly indicate the possible presence of defects in terms of much lower and higher values of isomer shifts associated with typical components of BiFeO 3 . Similarly the values of isomer shifts corresponding to the fractions f 3 and f 4 are also much lower as compared to the typical value of isomer shift corresponding to Fe 3+ 62 , 68 , 69 . However there is a decrease in the fraction of Fe atoms experiencing weak ferromagnetic interaction by close to 30%.…”

Magnetism of Nanoparticles: Effect of the Organic Coating

“…The type and the concentration of the organic molecule both during and after the synthesis process can produce significant changes in the morphology of the nanoparticle assembly, allowing to control the particle size and shape, their distribution and their arrangements (i.e., the degree and type of particles aggregation) strongly affecting the magnetic properties [ 39 , 40 , 53 , 54 , 55 ]. Many authors have investigated the effect of the oleic acid concentration on the particle size [ 40 , 54 , 55 ] and the morphology of nanoparticle assemblies.…”

“…The type and the concentration of the organic molecule both during and after the synthesis process can produce significant changes in the morphology of the nanoparticle assembly, allowing to control the particle size and shape, their distribution and their arrangements (i.e., the degree and type of particles aggregation) strongly affecting the magnetic properties [ 39 , 40 , 53 , 54 , 55 ]. Many authors have investigated the effect of the oleic acid concentration on the particle size [ 40 , 54 , 55 ] and the morphology of nanoparticle assemblies. The effect of the oleic acid concentration on the size, shape, morphology and agglomeration type on the magnetic properties of CoFe 2 O 4 particles was investigated by Jovanovic et al [ 55 ], who prepared the samples following the same procedure as in [ 54 ] using 0.1, 0.15, 0.2, 0.25, 0.5, and 2 M of surfactant.…”

“…The organic coating can also produce other changes that have a direct impact on the magnetic properties of an assembly of nanoparticles, such as: controlled change of the interparticle distance, functionalizing the particles with molecules of proper steric features, allowing in such a way a tuning of the strength of dipolar interparticle interactions, which contribute to the effective anisotropy [ 37 , 38 ]. controlled change, by specific ligands, of morpho-structural features of the particle assembly, i.e., size, shape and the crystalline structure of NPs during the synthesis process, strongly affecting the resulting magnetic state and its thermal stability [ 39 , 40 , 41 ]. …”

“…controlled change, by specific ligands, of morpho-structural features of the particle assembly, i.e., size, shape and the crystalline structure of NPs during the synthesis process, strongly affecting the resulting magnetic state and its thermal stability [ 39 , 40 , 41 ].…”